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.. _glossary:
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********
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Glossary
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********
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The glossary is partly extracted from New Manual of Observatory Practice and some information
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is taken from Modern Global Seismology.
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|scname| terms
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==============
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.. glossary::
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binding
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A binding is a set of configuration options to configure the connection between a
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:term:`module` and a station. Bindings are located in ``etc/key/modulename/station_NET_STA``.
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They are either written to the database or used to create native configuration files
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for standalone modules. The concepts section on :ref:`configuration <concepts_configuration>`
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provides more details.
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module
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A module is usually a binary executable that does a certain job such as :ref:`seedlink`
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or :ref:`scautopick`. The concepts section on :ref:`modules <concepts_modules>`
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provides more details.
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plugin
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An extension to a module. The concepts section on :ref:`plugins <concepts_plugins>`
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provides more details.
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profile
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A profile is a special :term:`binding`. Instead of defining the same set of configuration
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options again and again for many stations a profile can be used. Instead of configuring a
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stations like:
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.. code-block:: sh
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seedlink
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scautopick
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which refers to ``etc/key/seedlink/station_NET_STA`` and ``etc/key/scautopick/station_NET_STA``
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a profile can be given:
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.. code-block:: sh
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seedlink:geofon
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scautopick:teleseismic
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which refers to :file:`etc/key/seedlink/profile_geofon` and
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:file:`etc/key/scautopick/profile_teleseismic`.
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Changing the profile changes the bindings of all stations that use this profile.
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RecordStream
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Interface to access data records from data processing modules.
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:term:`SeisComP` applications access waveform data through the
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:ref:`RecordStream interface <concepts_RecordStream>`.
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standalone module
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A module that needs to convert the configuration or do not use the default
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configuration options (see below) is called a standalone modules.
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Examples for standalone modules are :ref:`seedlink`, :ref:`slarchive` or :ref:`slmon`.
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trunk
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The module and library collection which forms and uses the SeisComP
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framework. The Application class is part of this framework. All trunk
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modules share a common configuration schema and a database with
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Inventory, EventParameters, Configuration, Routing and QC schemas.
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Representatives are :ref:`scautoloc` and :ref:`scautopick` and the GUI
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collection with :ref:`scolv`, :ref:`scmv`, :ref:`scrttv` and :ref:`scesv`.
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----
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Scientific and technical terms
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==============================
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.. glossary::
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AIC
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Aikaike Information Criterion used for refinement of phase picks.
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Phase pickers for picking P and S phase arrivals based on AIC may reach
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high accuracy if tuned well.
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aftershocks
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Earthquakes that follow a large earthquake in a sequence. They are smaller than the mainshock
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and within 1-2 fault lengths distance from the mainshock fault. Aftershocks can continue over
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a period of weeks, months, or years, decreasing in frequency with time. In general, the larger
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the mainshock, the larger and more numerous the aftershocks, and the longer they will continue.
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amplitude
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#. General term used for an observation of a wave at a particular time.
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#. QuakeML object. Amplitudes are computed, e.g. for computing :term:`magnitudes <magnitude>`
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of different types. Another type is the :term:`SNR`.
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Amplitude computation depends on the type.
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In |scname| magnitudes are computed automatically by :ref:`scautopick` and
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:ref:`scamp` or interactively by :ref:`scolv`.
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array
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A set of observing sensors at which the observed and sought signal are mostly coherent.
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If the sensors are seismometers or barometers measuring infrasound, the terms
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:term:`seismic array` or :term:`infrasound array` are used, respectively.
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Arrays are different from a :term:`network` by the applied methods, e.g.
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:term:`F-K` analysis, :term:`beam` forming or :term:`vespagram` analysis.
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ATF
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The :term:`array transfer function` or :term:`array response function`
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describes the sensitivity and resolution of an :term:`array` to signals
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propagating through the array with a particular :term:`azimuth`, :term:`slowness`
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and :term:`frequency`.
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array response function
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A synonym of :term:`ATF` or :term:`array transfer function`.
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array transfer function
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A synonym of :term:`ATF` or :term:`array response function`.
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ArcLink
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ArcLink complements :term:`SeedLink` by providing access to archived waveform
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data. Arclink was distributed with :term:`SeisComP` until version 3.0.
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arrival
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#. The appearance of seismic energy on a seismic record
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#. QuakeML object. The detected phase onset associated to an origin in |scname|.
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arrival time
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The time at which a particular phase of a seismic wave arrives at a station.
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asthenosphere
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The ductile part of the Earth, just below the brittle :term:`lithosphere`,
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in the upper mantle. The lithosphere/asthenosphere reaches down to about 200 km.
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azimuth
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In general a direction measured clock-wise in degrees against north. In seismology used to
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measure the direction from a seismic source to a seismic station recording this event.
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beam
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The sum of signals observed at an :term:`array` shifted with respect
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to the array reference coordinate assuming a particular :term:`slowness`
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and :term:`azimuth`. Optimum values for slowness and azimuth can be
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found, e.g. by :term:`F-K` analysis.
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beam packing
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Equivalent to the :term:`F-K` analysis where the :term:`beam` and the related
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parameters such as :term:`beam power` or :term:`semblance` are formed in the
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time domain. Seismograms from the :term:`array` stations are shifted according
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to the considered ranges of :term:`slowness` and :term:`backazimuth` or
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:term:`wave number` and summed to form the beam.
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beam power
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The energy of :term:`beam` within a defined time window.
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backazimuth
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The direction from the seismic station towards a seismic source, measured in degrees clock-wise
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against north; sometimes also just called azimuth.
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Benioff zone
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see :term:`Wadati-Benioff zone`
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body wave
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A seismic wave that propagates through the interior of the Earth, as opposed to
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surface waves that propagate near the Earth's surface. :term:`P<P wave>` and :term:`S waves<S wave>`, which shake
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the ground in different ways, are examples.
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body wave magnitude
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see :term:`magnitude, body-wave (mb)`
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calibration
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The process of determining the response function (distortion of the input signal) and
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sensitivity of an instrument or its derived component.
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CAV
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cumulated absolute velocity
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CI
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Characteristic Intensity
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channel code
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Description of characteristics of data related to the recording sensor and
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data logger as well as instrument responses, sampling frequencies, etc.
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The standard codes are defined in the :cite:t:`seed-2012`.
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Circum-Pacific belt
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The zone surrounding the Pacific Ocean that is characterized by frequent and strong
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earthquakes and many volcanoes as well as high tsunami hazard. Also called the Ring of Fire.
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coda
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The tail of a seismic signal, usually with exponentially decaying amplitudes, which
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follow a strong wave arrival. Coda waves are due to scattering and superposition of multi-path arrivals.
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coda phase
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A detection of a single phase of unknown path found within the coda signal envelope,
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designated as tx, e.g. Px or Sx.
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coherent
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Seismic signals detected on various seismic sensors of a seismic array or network are said to
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be coherent if they are related to each other in time, amplitude and/or waveform because they
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come from the same seismic source.
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color
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Colors are given in hexadecimal representation or by :term:`color keyword names <color keyword name>`.
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color keyword name
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Color keyword names allow the specification of color values by names
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representing color codes instead of RGB or hexadecimal representation. Find examples
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on the `website of W3C <https://www.w3.org/TR/SVG11/types.html#ColorKeywords>`_.
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Color keyword names have been introduced in SeisComP in version 4.4.0.
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convolution
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A mathematically equivalent operation that describes the action of a linear (mechanical
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and/or electronic) system on a signal, such as that of a filter on a seismic signal.
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core
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The innermost part of the Earth. The outer core extends from about 2900 to about 5120 km below
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the Earth's surface and consists in its main components of a mixture of liquid iron and nickel.
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The inner core is the central sphere of the Earth with a diameter of 1250 km and consists of solid metal.
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Core-Mantle Boundary(CMB)
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see :term:`Gutenberg discontinuity`
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corner frequency
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The frequency at which the curve representing the Fourier amplitude spectrum of a recorded seismic
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signal abruptly changes its slope. For earthquakes, this frequency is a property of the source and
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related to fault size, rupture velocity, source duration and stress drop in the source. Also the
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frequency at which the transfer function / magnification curve of a recording system changes its slope.
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creep
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Slow, more or less continuous movement occurring on faults due to ongoing tectonic deformation.
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Also applied to slow movement of landslide masses down a slope because of gravitational forces.
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Faults that are creeping do not tend to have large earthquakes. This fault condition is commonly
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referred to as unlocked.
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crust
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The outermost major layer of the Earth, ranging from about 10 to 70 km in thickness worldwide.
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The oceanic crust is thinner (about 10 to 15 km) than the continental crust (about 25 to 70 km).
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The uppermost 15-35 km of the crust is brittle enough to produce earthquakes. The seismogenic crust
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is separated from the lower crust by the brittle-ductile boundary. The crust is usually characterized
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by P-wave velocities below 8 km/s (average velocity of about 6 km/s).
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delay
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The time difference between the arrival time and the end time of the last record achieved plus
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the half record length. The delay can be computed by :ref:`scqc`.
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depth Phase
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see :term:`pP phase` or :term:`sP phase`
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detection
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Identification of an arrival of a seismic signal with amplitudes above and/or signal shape
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(waveform) different from seismic noise.
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directivity
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An effect of a propagating fault rupture whereby the amplitudes of the generated ground motions
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depend on the direction of wave propagation with respect to fault orientation and slip
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direction (radiation pattern). The directivity and thus the radiation pattern is different for
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:term:`P<P wave>` and :term:`S waves<S wave>`.
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EDA
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Effective Design Acceleration
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EIDA
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European Integrated Data Archive: http://www.orfeus-eu.org/data/eida/
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epicenter
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Vertical projection of the hypocenter to the surface.
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event
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#. General term used for a localized disturbance (earthquake, explosion, etc.) which generates seismic waves.
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#. QuakeML object. The event is the parent object of several :term:`origins <origin>`.
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Among these origins a preferred origin
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and its :term:`preferred magnitude` is selected to represent the event.
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An event can be seen as an earthquake folder
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which contains information about earthquake parameters.
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fault-plane solution
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Representation of the fault activated in an earthquake and the caused direction of slip on the fault by
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a circle with two intersecting curves looking like a beach ball. A fault-plane solution is found by the
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analysis of seismic records at many stations of an earthquake to obtain the radiation pattern. From the
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radiation pattern the fault parameter and the slip direction are determined using a stereographic
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projection or its mathematical equivalent. The most common analysis uses the direction of first motion
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of P wave onsets and yields two possible orientations for the fault rupture and the direction of seismic
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slip. Another technique is to use the polarization of teleseismic :term:`S waves<S wave>` and/or to measure amplitude
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ratios between different phase types. Further inferences can be made from these data concerning the
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principal axes of stress in the region of the earthquake. The principal stress axes determined by this
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method are the compressional axis (also called the P-axis, i.e. the axis of greatest compression, or s1),
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the tensional axis (also known as the T-axis, i.e., the axis of least compression, or s3), and the
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intermediate axis (s2).
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filter(ing)
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A filter attenuates certain frequencies of a (seismic) signal and amplifies others. The process of
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filtering can be accomplished electronically while recording or numerically in a computer. Filtering also
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occurs naturally as seismic energy passes through the Earth.
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The available and integrated filters in |scname| are documented in :ref:`filter-grammar`.
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first motion
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The first noticeable displacement in a seismogram caused by the arrival of a P wave at the seismometer.
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Upward motion of the ground at the seismometer indicates a dilatation at the source, downward motion
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indicates a compression. Due to the presence of seismic noise the proper polarity of the first motion
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may be difficult to recognize.
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F-K
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F-K refers to a 2-D :term:`Fourier analysis` where the base functions
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are defined, e.g. by ranges of :term:`frequency` and :term:`wave number`.
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F-K analysis is applied for signal detection by transforming time series
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recorded at several sensors, e.g. seismic or infrasound :term:`array`
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stations to the time and space domain.
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The equivalent to F-K analysis in the time domain is :term:`beam packing`.
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focal mechanism
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see :term:`fault-plane solution`
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foreshocks
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Earthquakes that occur in a series of earthquakes before the largest earthquake, termed the mainshock.
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Foreshocks may precede the mainshock by seconds to weeks and usually originate at or near the focus
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of the larger earthquake. Not all mainshocks have foreshocks.
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Fourier spectrum
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The relative amplitudes (and phase angles) at different frequencies that are derived from a time series
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by Fourier analysis.
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Fourier analysis
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The mathematical operation that resolves a time series (for example, a recording of ground motion)
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into a series of numbers that characterize the relative amplitude and phase components of the signal
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as a function of frequency.
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frequency
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Number of cycles of a repeating signal per unit time, typically per second.
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frequency domain
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The transformation of a seismic signal from the time domain (as a seismogram) to the frequency
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domain is conducted by a :term:`Fourier analysis`. The signal is represented in the frequency domain by
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the amplitude and phase components as a function of frequency (see spectrum). The representations of
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a seismic signal in the time and in the frequency domain are equivalent in a mathematical sense.
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For some procedures of data analysis the time-domain representation of a seismic record is more
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suitable while for others the frequency-domain approach is more appropriate and efficient.
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gempa GmbH
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`gempa GmbH <http://www.gempa.de/>`_ is a spin-off from :term:`GFZ`
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offering a range of services and products to monitor, process and analyze
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seismicity. It is the main development and service company for |scname|.
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GEOFON
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GEOFON (https://geofon.gfz-potsdam.de) is part of the Modular Earth Science
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Infrastructure (MESI) at :term:`GFZ`.
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geometrical spreading
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The component of reduction in wave amplitude due to the radial spreading of seismic energy with
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increasing distance from a given source.
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GFZ
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Helmholtz Centre Potsdam `German Research Centre for Geosciences <http://www.gfz-potsdam.de/>`_.
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|scname| was originally developed at GFZ.
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GMPE
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Ground Motion Prediction Equation
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Green's function
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A mathematical representation that, in reference to earthquake shaking, is used to represent the
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ground motion caused by instantaneous slip on a small part of a fault. Green’s functions can be
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summed over a large fault surface to compute the ground shaking for a large earthquake rupturing
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a fault of finite size. The fractional fault-slip events that are summed can be records from
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small earthquakes on the fault or they can be theoretically computed small-earthquake records.
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Gutenberg discontinuity
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The seismic velocity discontinuity marking the core-mantle boundary (CMB) at which the velocity
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of P waves drops from about 13.7 km/s to about 8.0 km/s and the velocity of :term:`S waves<S wave>` drops from
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about 7.3 km/s to 0 km/s. The CMB reflects the change from the solid mantle material to the
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fluid outer core.
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GUI
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Graphical use interface, e.g. :ref:`scolv`.
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hypocenter
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Coordinates of an earthquake point source. Hypocenters based on :term:`P<P wave>` and :term:`S wave`
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first arrivals point to the place where the rupture process starts. For large earthquakes the
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source location determined by :term:`P wave` first arrivals can differ significantly from the location of
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maximum energy release.
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Ia
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Arias Intensity
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infrasound array
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An :term:`array` of barometers measuring infrasound signals.
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intensity
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A measure of the effects of an earthquake at a particular place at the Earth's surface on humans
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and (or) structures. The intensity at a point depends not only upon the strength of the earthquake
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(magnitude) but also upon the distance from the earthquake, the depth of the hypocenter and the
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local geology at that point. Several scales exist, most of them giving the intensity in 12 degrees,
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usually written as Roman numerals. Most frequently used are at present the European Macroseismic
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Scale (EMS-98), and in the United States the Modified Mercalli scale and the Rossi-Forel scale.
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There are many different intensity values for one earthquake, depending on how far you are away
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from the epicenter; this is unlike the magnitude value, which is one number for each earthquake
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as a measure of the amount of seismic wave energy released by it.
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interplate/intraplate
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Intraplate pertains to processes within the Earth's crustal plates. Interplate pertains to
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processes between the plates.
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interplate coupling
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The qualitative ability of a subduction thrust fault to lock and accumulate stress. Strong
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interplate coupling implies that the fault is locked and capable of accumulation stress whereas
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weak coupling implies that the fault is unlocked or only capable of accumulating low stress.
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A fault with weak interplate coupling could be aseismic or could slip by creep.
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inventory
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The inventory is the collection of all available meta data related to :term:`network`,
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:term:`station`, :term:`location code`, station :term:`channel code`,
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characteristics of sensors and data loggers, etc. More details are given in
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the concepts section :ref:`concepts_inventory`.
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latency
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Time difference between the end times of consecutive records.
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The latency can be computed by :ref:`scqc`.
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lithosphere
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The outer solid part of the Earth, including crust and uppermost mantle. The lithosphere is
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about 100 km thick, although its thickness is age-dependent (older lithosphere is thicker).
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At some locations the lithosphere below the crust is brittle enough to produce earthquakes by
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faulting, such as within a subducted oceanic plate.
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location code
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|
Description of particular sensor location associated to a station. The standard
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location codes are defined in the :cite:t:`seed-2012`.
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Love wave
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|
A major type of surface waves having a horizontal motion that is transverse (or perpendicular)
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to the direction of propagation. It is named after A. E. H. Love, the English mathematician
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|
who discovered it.
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leaky mode
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A seismic surface wave which is imperfectly trapped, e.g., within a low-velocity layer or a
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sequence of layers, so that its energy leaks or escapes across a layer boundary causing some
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attenuation.
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low-velocity layer/zone
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Any layer in the Earth in which seismic wave velocities are lower than in the layers above and below.
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magnification curve
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|
A diagram showing the dependence of amplification, e.g. of the seismic ground motion by a
|
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|
seismograph, as a function of frequency.
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magnitude
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|
A number that characterizes the relative size of an earthquake. The magnitude is based on
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|
:term:`amplitude` measurement of the maximum motion recorded by a seismograph
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|
(sometimes for waves of a particular frequency),
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|
corrected for the attenuation with distance. Several scales have been defined, but the most commonly used are:
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#. local magnitude (ML), commonly referred to as "Richter magnitude"
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#. surface-wave magnitude (Ms)
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#. body-wave magnitude (mb)
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#. moment magnitude (Mw).
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|
The magnitude scales 1-3 have limited range and applicability and do not
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|
satisfactorily measure the
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|
|
size of the largest earthquakes. The moment magnitude (Mw) scale, based on
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|
the concept of seismic moment,
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|
is uniformly applicable to all earthquake sizes but is more difficult to
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|
compute than the other types. In
|
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|
principal, all magnitude scales could be cross calibrated to yield the same
|
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|
|
value for any given earthquake, but
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|
this expectation has proven to be only approximately true, thus the
|
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|
|
magnitude type as well as its value is needed to be specified.
|
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|
Additional or modified magnitudes can be computed by providing plugins.
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In |scname| magnitudes are computed automatically by :ref:`scmag` or interactively
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|
by :ref:`scolv`.
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magnitude, local (ML)
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|
Magnitude scale introduced by Richter in the early 1930s (:cite:t:`richter-1935`)
|
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|
|
to have a common scale for the strength of earthquakes. The basic observation
|
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|
|
is the systematic decay of the logarithm of the maximum
|
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|
|
amplitudes with increasing distance for different earthquakes described by:
|
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|
|
|
|
|
|
.. math::
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|
ML = \log A_{max} - \log A_0
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|
with A\ :sub:`0` as amplitude of a reference event. For the reference event
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|
ML = 0 the formula can be rewritten to
|
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|
|
|
|
|
|
|
.. math::
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|
ML = \log A_{max} - 2.48 + 2.76 \log \Delta
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|
with Δ being the distance of the station to the earthquake location. ML is a
|
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|
magnitude scale for
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|
recordings of earthquakes smaller than ML 7 at regional stations. It is
|
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|
|
usually a measure of the
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|
regional-distance S-wave on horizontal component records.
|
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|
The original formula is only valid for records from a Wood-Anderson torsion
|
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|
|
seismometer with a natural period of
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|
|
0.8 s and shallow earthquakes in California. Therefore calibration functions
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|
for other regions and wider depth ranges are necessary.
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|
A Wood-Anderson seismometer is simulated.
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For amplitudes measured on the vertical component records, additional
|
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|
correction factors have to be applied. ML saturates at
|
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|
|
magnitudes around 7 because the maximum amplitudes of larger earthquakes
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|
occur at longer periods than
|
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|
|
the bandpass of 0.1 s and 3 s for the magnitude calculation.
|
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In |scname| a modified local magnitude
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|
:term:`MLv <magnitude, local vertical (MLv)>` is determined by simulation
|
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|
|
of a Wood-Anderson instrument and then measuring the amplitude in a 150 s
|
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|
time window on the vertical component of station with distances smaller than 8°.
|
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|
* Amplitude unit in |scname|: **millimeter** (mm)
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|
Read the :ref:`technical documentation <global_ml>` for more details and
|
|
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|
|
the configuration.
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|
magnitude, local custom (MLc)
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|
The local magnitude measured on the horizontal components with
|
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|
|
custom parametric calibration function, configurable amplitude filtering,
|
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|
|
Wood-Anderson simulation and distance measure.
|
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|
* Amplitude unit in |scname|: **millimeter** (mm)
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|
Read the :ref:`technical documentation <global_mlc>` for more details and
|
|
|
|
|
the configuration.
|
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|
|
magnitude, local horizontal (MLh)
|
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|
|
The local magnitude computed from amplitudes measured on the horizontal
|
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|
|
components with a modified parametric calibration function as compared to
|
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|
|
:term:`ML <magnitude, local (ML)>`.
|
|
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|
|
* Amplitude unit in |scname|: **millimeter** (mm)
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|
Read the :ref:`technical documentation <global_mlh>` for more details and
|
|
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|
|
the configuration.
|
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|
|
magnitude, local GNS/GEONET (MLr)
|
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|
|
Local magnitude calculated from :term:`MLv <magnitude, local vertical (MLv)>`
|
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|
|
amplitudes based on GNS/GEONET specifications for New Zealand.
|
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|
Read the :ref:`technical documentation <global_mlr>` for more details and the configuration.
|
|
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|
|
magnitude, local vertical (MLv)
|
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|
|
The :term:`ML <magnitude, local (ML)>` magnitude with amplitudes measured on
|
|
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|
|
the vertical component instead of the horizontals.
|
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|
|
* Amplitude unit in |scname|: **millimeter** (mm)
|
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|
Read the :ref:`technical documentation <global_mlv>` for more details and the configuration.
|
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|
magnitude, Nuttli (MN)
|
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|
|
Nuttli magnitude for Canada and other Cratonic regions.
|
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|
|
* Amplitude unit in |scname|: **meter/second** (m/s)
|
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|
Read the :ref:`technical documentation <global_mn>` for more details and the configuration.
|
|
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|
|
magnitude, body-wave (mb)
|
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|
|
Magnitude developed for teleseismic body waves. mb is defined on the amplitude
|
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|
|
of the first few cycles of the P-wave restituted to :term:`WWSSN_SP`.
|
|
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|
|
|
* Amplitude unit in |scname|: **nanometer** (nm)
|
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|
|
Read the :ref:`technical documentation <global_mb>` for more details and the configuration.
|
|
|
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|
|
|
magnitude, broadband body-wave (mB_BB)
|
|
|
|
|
mB_BB is the term recommended by the IASPEI commission for
|
|
|
|
|
:term:`magnitude, broadband body-wave (mB)` which is used in |scname|.
|
|
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|
|
|
|
|
|
|
magnitude, broadband body-wave (mB)
|
|
|
|
|
mB is a magnitude based on body waves like :term:`mb <magnitude, body-wave (mb)>`,
|
|
|
|
|
but with the amplitude measured in a broad frequency range and longer time windows.
|
|
|
|
|
mB is used as a synonym for :term:`mB_BB <magnitude, broadband body-wave (mB_BB)>`.
|
|
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|
|
|
|
|
|
* Amplitude unit in |scname| is **nanometer per second** (nm/s)
|
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|
|
Read the :ref:`technical documentation <global_mb_bb>` for more details and the configuration.
|
|
|
|
|
|
|
|
|
|
magnitude, cumulative body-wave (mBc)
|
|
|
|
|
mBc is the cumulative body-wave magnitude. See :cite:t:`bormann-2005`
|
|
|
|
|
and :cite:t:`bormann-2009` for details.
|
|
|
|
|
|
|
|
|
|
magnitude, surface wave (Ms)
|
|
|
|
|
Ms is a magnitude scale based on teleseismic surface waves. Historically, Ms
|
|
|
|
|
is based on measurements of
|
|
|
|
|
the maximum horizontal true ground motion displacement amplitudes
|
|
|
|
|
|
|
|
|
|
.. math::
|
|
|
|
|
|
|
|
|
|
A_{Hmax} =\sqrt{{A_N}^2 + {A_E}^2}
|
|
|
|
|
|
|
|
|
|
in the total seismogram at periods around 20 s. For shallow earthquakes the dominant
|
|
|
|
|
long-period signals are the surface waves. The period of 20 s corresponds to the Airy
|
|
|
|
|
phase, a local minimum in the group velocity dispersion curve of Rayleigh surface waves.
|
|
|
|
|
For measuring amplitudes a correction for the WWSSN_LP instrument response is applied.
|
|
|
|
|
|
|
|
|
|
The Moscow-Prague equation for surface wave magnitude is given by
|
|
|
|
|
|
|
|
|
|
.. math::
|
|
|
|
|
|
|
|
|
|
M_s = \log \left(\frac{A_{Hmax}}{T}\right) + 1.66 \log(\Delta) + 3.3
|
|
|
|
|
|
|
|
|
|
where T is the measured period.
|
|
|
|
|
|
|
|
|
|
.. math::
|
|
|
|
|
|
|
|
|
|
M_s = \log \left(\frac{A}{T}\right)max + 1.66 \log(\Delta) + 3.3
|
|
|
|
|
|
|
|
|
|
Here, the maximum ground particle velocity, (A/T)max, is used instead of the AHmax to
|
|
|
|
|
allow a broader spectrum of dominant periods. This formula is valid for distances of
|
|
|
|
|
2° to 160° and source depths smaller than 50 km.
|
|
|
|
|
|
|
|
|
|
* Amplitude unit in |scname| is **meter per second** (m/s)
|
|
|
|
|
|
|
|
|
|
magnitude, surface wave (Ms_20)
|
|
|
|
|
Ms_20 is the :term:`Ms <magnitude, surface wave (Ms)>` surface-wave magnitude
|
|
|
|
|
at *T=20* s period based on the recommendations
|
|
|
|
|
by the IASPEI magnitude working group issued on 27 March, 2013.
|
|
|
|
|
|
|
|
|
|
* Amplitude unit in |scname|: nanometer (nm)
|
|
|
|
|
|
|
|
|
|
Read the :ref:`technical documentation <global_ms_20>` for more details and the configuration.
|
|
|
|
|
|
|
|
|
|
magnitude, broadband surface wave (Ms(BB))
|
|
|
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|
Ms(BB) is a broadband magnitude scale based on teleseismic surface waves.
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In contrast to :term:`Ms <magnitude, surface wave (Ms)>`, amplitudes for Ms(BB)
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are measured as the maximum on vertical true ground motion velocity seismograms without
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instrument simulation or restitution.
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The Moscow-Prague equation for surface wave magnitude is applied as given by
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.. math::
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M_s = \log \left(\frac{A}{2\pi}\right) + 1.66 \log(\Delta) + 3.3
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* Amplitude unit in |scname|: **meter per second** (m/s)
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* Period range: all
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* Distance range: 2 - 160°
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* Depth range: 0 - 100 km
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* Time window: distance (km) / 3.5 km/s + 30 s
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magnitude, duration (Md)
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The duration magnitude measured on the coda wave train.
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Read the :ref:`technical documentation <global_md>` for more details and the configuration.
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magnitude, JMA (M_JMA)
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M(JMA) is a magnitude similar to the Ms, but the formula is calibrated for instruments
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with 5 s period at local distances. The data set for the calibration was gained by the
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Japan Meteorological Agency (JMA).
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.. math::
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M(JMA) = \log \sqrt{{A_N}^2 + {A_E}^2} + 1.73 \log\Delta - 0.83
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This equation is valid for local (< 2000 km) and shallow (< 80 km)
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earthquakes. For deeper earthquakes additional correction functions have
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to be applied (:cite:t:`katsumata-1996`).
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* Amplitude unit in |scname|: **micrometer** (um)
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* Time window: 150 s
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* Epicentral distance range: 0 - 20°
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* Depth range: 0 - 80 km
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magnitude, moment (Mw)
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The moment magnitude is a magnitude scale related to the seismic moment M\ :sub:`0` and
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thus to the released seismic energy.
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To obtain Mw the seismic moment is first determined, e.g. by a moment tensor inversion.
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Then the Mw is gained by the following standard relationship between seismic moment
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and the moment magnitude (M\ :sub:`0` in cgs units of dyn*cm):
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.. math::
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Mw = \frac{2}{3}(\log M_0 - 16.1)
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This equation is analog to the relation between M\ :sub:`s` and M\ :sub:`0`.
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magnitude, averaged moment (Mw(avg))
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Moment magnitude derived as a weighted average of other magnitudes.
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magnitude, broadband P-wave moment (Mwp)
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The Mwp is a rapid estimate of the moment magnitude based on the
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first-arrival P waves on broadband seismograph records. The displacement
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seismograms of the P wave portion are considered as source time function
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approximation. The seismic moment is estimated for each station by
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integrating the displacement records. The combination of multiple records
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results in an estimation of the moment magnitude without correction
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for the source mechanism (:cite:t:`tsuboi-1995`).
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* Amplitude unit in |scname|: **nanometer times second** (nm*s)
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* Time window: 95 s
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* Epicentral distance range: 5 - 105°
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magnitude, derived mB (Mw(mB))
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Moment magnitude derived from :term:`mB <magnitude, broadband body-wave (mB)>`
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magnitudes using linear conversion:
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Mw(mB) = 1.30 mB - 2.18
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magnitude, derived Mwp (Mw(Mwp))
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Moment magnitude derived from :term:`Mwp <magnitude, broadband P-wave moment (Mwp)>`
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magnitudes using linear conversion after :cite:t:`whitmore-2002`:
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Mw(Mwp) = 1.31 Mwp - 1.91
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magnitude, summary (M)
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Summary magnitude derived from multiple other magnitudes by :ref:`scmag`.
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mainshock
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The largest earthquake in a sequence, sometimes preceded by one or more foreshocks,
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and almost always followed by many aftershocks.
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mantle
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The part of the Earth's interior between the core and the crust.
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microearthquake
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An earthquake that is not perceptible by man and can be recorded by seismographs only.
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Typically, a microearthquake has a magnitude of 2 or less on the Richter scale.
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microseism
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#. In a broader sense: A more or less continuous motion in the Earth in a wide frequency
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range that is unrelated to any earthquake and caused by a variety of usually uncorrelated
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(incoherent) natural and artificial (man-made) sources.
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#. In a more specific sense: That part of seismic noise that is generated by wave motions
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on lakes and oceans and their interaction with shores, typically with periods between
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about 2 to 9 s (the stronger secondary microseisms), and 11 to 18 s (the weaker
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primary microseisms).
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miniSeed
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miniSEED is the
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standard for the exchange of seismic time series. It uses a fixed record
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|
length and applies data compression as defined in :cite:t:`seed-2012`.
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MMI
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Modified Mercalli Intensity
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Moho
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The abbreviation for the :term:`Mohorovičić discontinuity`.
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Mohorovičić discontinuity
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|
The discontinuity in seismic velocities that defines the boundary between crust and mantle
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|
of the Earth. Named after the Croatian seismologist Andrija Mohorovičič (1857-1936) who
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discovered it. The boundary is between 20 and 60 km deep beneath the continents and between
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5 and 10 km deep beneath the ocean floor.
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moment tensor
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Moment tensors or seismic moment tensors describe the equivalent forces
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due to seismic point sources, e.g. earthquakes with rupture dimensions
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much smaller than the distance at which they are observed.
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network
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A set of stations typically maintained by one or more institutions and
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tuned to record particular signals.
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network magnitude
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a. The network magnitude is a magnitude value summarizing several :term:`station magnitude` values
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|
of one :term:`origin`. Read the documentation of :ref:`scmag` for the details.
|
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|
#. QuakeML object.
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noise (seismic)
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|
Incoherent natural or artificial perturbations caused by a diversity of agents and
|
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|
|
distributed sources. One usually differentiates between ambient background noise and
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|
|
instrumental noise. The former is due to natural (ocean waves, wind, rushing waters,
|
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|
|
animal migration, ice movement, etc.) and/or man-made sources (traffic, machinery, etc.),
|
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|
|
whereas instrumental (internal) noise may be due to the flicker noise of electronic
|
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|
|
components and/or even Brownian molecular motions in mechanical components. Digital
|
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|
|
data acquisition systems may add digitization noise due to their finite discrete
|
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|
|
resolution (least significant digit). Very sensitive seismic recordings may contain
|
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|
|
all these different noise components, however, usually their resolution is tuned so
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|
|
that only seismic signals and to a certain degree also the ambient noise are resolved.
|
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|
|
Disturbing noise can be reduced by selecting recording sites remote from noise sources,
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|
|
installation of seismic sensors underground (e.g., in boreholes, tunnels or abandoned
|
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|
|
mines) or by suitable filter procedures (improvement of the signal-to-noise ratio).
|
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|
Nyquist frequency
|
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|
|
Half of the digital sampling rate. It is the minimum number of counts per second
|
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|
|
needed to define unambiguously a particular frequency. If the seismic signal contains
|
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|
|
energy in a frequency range above the Nyquist frequency the signal distortions are
|
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|
|
called aliasing.
|
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onset
|
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|
|
The first appearance of a seismic signal on a record.
|
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origin
|
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|
|
#. Location (hypocenter), Time and strength estimation of an earthquake based on seismic
|
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|
|
phases and amplitudes
|
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|
|
#. QuakeML object
|
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|
|
origin time
|
|
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|
|
Estimated source time of an event belonging to a certain origin; describes the
|
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|
|
rupture start time. Attribute of the QuakeML object Origin, see :term:`origin`.
|
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|
phase
|
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|
|
#. A stage in periodic motion, such as wave motion or the motion of an oscillator,
|
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|
|
measured with respect to a given initial point and expressed in angular measure.
|
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|
|
#. A pulse of seismic energy arriving at a definite time, which passed the Earth
|
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|
|
on a specific path.
|
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|
|
#. Attribute of the QuakeML object Arrival, see :term:`arrival`.
|
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|
P phase
|
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|
|
The P phase is the arrival of the direct P wave that traveled through the Earth's
|
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|
|
crust and mantle observed in epicentral distances up to 100°.
|
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|
Pdiff phase
|
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|
|
The long-period P-wave energy can be diffracted at the CMB forming at distances larger
|
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|
|
than 100° the Pdiff phase. The reason for the diffraction is the large reduction of the
|
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|
|
P wave velocity at the CMB from about 13.7 km/s to 8 km/s. The amplitude of Pdiff is
|
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|
|
relatively small. Pdiff is observed at distances where the outer core forms the "core
|
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|
|
shadow" (see also :term:`PKP phase`).
|
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|
Pg phase
|
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|
|
Pg is the direct P wave arriving first in local distances less than 100 km. For larger
|
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|
distances Pn arrives first (see :term:`Pn phase` for details).
|
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PGA
|
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|
|
Peak Ground Acceleration
|
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PGD
|
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|
|
Peak Ground Displacement
|
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PGV
|
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|
|
Peak Ground Velocity
|
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|
Pn phase
|
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|
|
Pn is the P head wave along the Moho arriving first at local distances larger than
|
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|
|
100 km (depending on the crustal thickness). Pn has usually smaller amplitudes than Pg.
|
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|
PcP phase
|
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|
|
The P wave that is reflected at the CMB forms the PcP. At epicentral distances between
|
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|
|
30° and 55° PcP is often recorded as sharp pulse.
|
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|
|
PKiKP phase
|
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|
|
|
A P wave that travels through the Earth's crust and mantle and is reflected at the
|
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|
|
outer core-inner core boundary. At distances between 100° and 113° PKiKP can be the
|
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|
|
first arrival if no Pdiff is observed.
|
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|
|
PKP phase
|
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|
|
The direct P waves traversing the Earth's crust, mantle and outer core without
|
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|
|
reflection is called PKP. The outer core is a fluid causing a strong refraction at
|
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|
|
the CMB into the outer core. The strong refraction of the seismic rays into the
|
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|
|
core causes a “core shadow” that commences at epicentral distances of around 100° and
|
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|
|
stretches to around 140°. Only Pdiff can be observed in this distance range. PKP is
|
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|
|
the first arrival at distances larger than around 143°. At a distance of 144° P waves
|
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|
|
with several paths through the Earth’s core arrive at the same time (caustic) and
|
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|
|
form a strong arrival.
|
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|
|
PP phase
|
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|
|
PP is a reflected P wave at the Earth's surface traversing the Earth's crust and mantle.
|
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|
|
pP phase
|
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|
|
A P wave that has a takeoff angle of greater than 90° at the source and therefore
|
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|
|
is first reflected at the surface near the epicenter. The pP is a depth phase.
|
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|
|
For shallow events and at teleseismic distances pP has nearly the same path as the P wave except
|
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|
|
for the path from hypocenter of the earthquake to the reflection point at the surface.
|
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|
|
SEED
|
|
|
|
|
Standard for the Exchange of Earthquake Data, a data format for seismological
|
|
|
|
|
data and metadata (:term:`inventory`).
|
|
|
|
|
It is controlled as a standard by the International Federation
|
|
|
|
|
of Digital Seismograph Networks (FDSN).
|
|
|
|
|
The current version is 2.4, updated August 2012.
|
|
|
|
|
Read :cite:t:`seed-2012` for details.
|
|
|
|
|
|
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|
|
S phase
|
|
|
|
|
The S phase is the arrival of the direct :term:`S wave` that traveled through the Earth's
|
|
|
|
|
crust and mantle observed in epicentral distances up to 100°.
|
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|
|
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|
|
Sg phase
|
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|
|
Sg is the direct :term:`S wave` arriving first in local distances less than 100 km. For larger
|
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|
distances Sn arrives first (see :term:`Sn phase` for details).
|
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|
Sn phase
|
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|
|
Sn is the S head wave along the Moho arriving first at local distances larger than
|
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|
|
100 km (depending on the crustal thickness). Sn has usually smaller amplitudes than Sg.
|
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|
|
sP phase
|
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|
|
A P wave starting as an :term:`S phase` at the source and arriving as P.
|
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|
|
The S phase has a takeoff angle greater than 90° at the source and therefore
|
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|
|
is first reflected at the surface near the epicenter and then converted into
|
|
|
|
|
a :term:`P wave` phase. The sP is therefore a depth phase. For shallow
|
|
|
|
|
events and at teleseismic distances sP has nearly the same path as the P
|
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|
|
|
wave except for the path from hypocenter of the earthquake to the
|
|
|
|
|
reflection point at the surface.
|
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|
|
|
|
|
|
|
pick
|
|
|
|
|
#. Automatic or manual determined phase onset
|
|
|
|
|
#. QuakeML object
|
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|
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|
|
polarity
|
|
|
|
|
In seismology the direction of first motion on a seismogram, either up (positive, compression)
|
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|
|
|
or down (negative, dilatation or relaxation).
|
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|
|
|
|
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|
|
polarization
|
|
|
|
|
The shape and orientation in space of the ground-motion particle trajectory. It differs
|
|
|
|
|
for different types of seismic waves such as P, S and surface waves and may be ± linear
|
|
|
|
|
or elliptical, prograde or retrograde. It is also influenced by heterogeneities and
|
|
|
|
|
anisotropy of the medium in which the seismic waves propagate and depends on their
|
|
|
|
|
frequency or wavelength, respectively. The polarization of ground motion may be reconstructed
|
|
|
|
|
by analyzing three-component seismic recordings.
|
|
|
|
|
|
|
|
|
|
preferred magnitude
|
|
|
|
|
#. The network magnitude representing the strength of an event best as
|
|
|
|
|
automatically selected by :ref:`scevent` or interactively.
|
|
|
|
|
#. Attribute of the QuakeML object Event, see :term:`event`.
|
|
|
|
|
|
|
|
|
|
preferred origin
|
|
|
|
|
#. The origin representing the location of an event best; generally, the location based
|
|
|
|
|
on the most picks or reviewed/revised by an operator. The preferred origins
|
|
|
|
|
is automatically selected by :ref:`scevent` or interactively.
|
|
|
|
|
#. Attribute of the QuakeML object Event, see :term:`event`.
|
|
|
|
|
|
|
|
|
|
QuakeML
|
|
|
|
|
A XML scheme developed as an open standard for seismological meta data
|
|
|
|
|
exchange (http://www.quakeml.org).
|
|
|
|
|
|
|
|
|
|
radiation pattern
|
|
|
|
|
Dependence of the amplitudes of seismic :term:`P<P wave>` and :term:`S waves<S wave>` on the direction and take-off
|
|
|
|
|
angle under which their seismic rays have left the seismic source. It is controlled
|
|
|
|
|
by the type of source mechanism, e.g., the orientation of the earthquake fault plane
|
|
|
|
|
and slip direction in space.
|
|
|
|
|
|
|
|
|
|
Rayleigh wave
|
|
|
|
|
A seismic surface wave causing a retrograde, elliptical motion of a particle at the free
|
|
|
|
|
surface, with no transverse motion. It is named after Lord Rayleigh (1842-1919), who
|
|
|
|
|
predicted its existence.
|
|
|
|
|
|
|
|
|
|
ray theory
|
|
|
|
|
Theoretical approach, which treats wave propagation as the propagation of seismic rays.
|
|
|
|
|
It is an approximation, which yields good results for short wave length (high-frequency
|
|
|
|
|
approximation) and allows easy calculations of travel times.
|
|
|
|
|
|
|
|
|
|
ray-tracing method
|
|
|
|
|
Computational method of calculating ground-shaking estimates that assumes that the
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ground motion is composed of multiple arrivals of seismic rays and related energy
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bundles (Gauss beams) that leave the source and are reflected or refracted at velocity
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boundaries according to Snell's Law. The amplitudes of reflected and refracted waves
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at each boundary are recalculated according to the Law of Conservation of Energy.
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recurrence interval
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The average time span between large earthquakes at a particular site. Also
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termed 'return period'.
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reflection
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The energy or wave from a seismic source that has been returned (reflected) from an
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interface between materials of different elastic properties within the Earth, just
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as a mirror reflects light.
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refraction
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The deflection, or bending, of the ray path of a seismic wave caused by its passage
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from one material to another having different elastic properties.
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Bending of a tsunami wave front owing to variations in the water depth along a coastline.
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relaxation theory
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A concept in which radiated seismic energy is released from stored strain energy
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during the slip along a fault until the adjacent fault blocks reach a new state of equilibrium.
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residual
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#. The difference between the measured and predicted values of some quantity (e.g., theoretical
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and measured phase arrival time).
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#. Attribute of QuakeML object Arrival, see :term:`arrival`.
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Ring of Fire
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The zone of volcanoes and earthquakes surrounding the Pacific Ocean which is called
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the Circum-Pacific belt; about 90% of the world's earthquakes occur there. The next
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most seismic region (5 - 6 % of earthquakes) is the Alpide belt.
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RMS
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Abbreviation for :term:`root mean square <root mean square (RMS)>`
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root mean square (RMS)
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Also referred to as :term:`RMS`. A statistical measure of the magnitude of a varying quantity defined as
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.. math::
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RMS = \sqrt{\frac{{x_1}^2 + {x_2}^2 + {x_3}^2 + ... + {x_n}^2}{N}}
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for the time series with the N elements x\ :sub:`1` to x\ :sub:`n`.
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rupture front
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The instantaneous boundary between the slipping and locked parts of a fault during
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an earthquake. A rupture propagating in one direction on the fault is referred to
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as unilateral. A rupture may radiate outward in a circular manner or it may radiate
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towards the two ends of the fault from an interior point, behavior referred to as
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bilateral.
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rupture velocity
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The speed at which a rupture front moves across the surface of the fault during
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an earthquake.
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SCML
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:term:`SeisComP` Markup Language. SCML is a flavor of `QuakeML
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|
<https://quake.ethz.ch/quakeml/>`_ and is used by |scname| and by
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products of :term:`gempa GmbH` for exchange. For details read the
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`UML diagram <https://geofon.gfz-potsdam.de/_uml/>`_.
|
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SDS
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|scname| Data Structure which is used for archiving waveform data. Below the
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base directory of the archive the SDS has the structure:
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.. code-block:: sh
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archive
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+ year
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+ network code
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+ station code
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+ channel code
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+ one file per day and location, e.g. NET.STA.LOC.CHAN.D.YEAR.DOY
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SED
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|
Specific Energy Density
|
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SeedLink
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|
SeedLink :cite:p:`seedlink` is a
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real-time data acquisition protocol and a client-server software that
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implements this protocol
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SeisComP
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SeisComP is likely the most widely distributed software package for
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seismological data acquisition and real-time data exchange over internet.
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Its data transmission protocol SeedLink became a de facto world standard.
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|
The first version of SeisComP was developed for the `GEOFON
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<http://geofon.gfz-potsdam.de/geofon/>`_ network and further extended
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|
within the MEREDIAN project under the lead of `GEOFON
|
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|
|
<http://geofon.gfz-potsdam.de/geofon/>`_/`GFZ
|
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|
|
<http://www.gfz-potsdam.de/>`_ Potsdam and `ORFEUS
|
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|
|
<http://www.orfeus-eu.org/>`_. Originally SeisComP was designed as a high
|
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|
|
standard fully automatic data acquisition and (near-)real-time data
|
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|
processing tool including quality control, event detection and location as
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well as dissemination of event alerts. In the context of the `GITEWS
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|
<http://www.gitews.de/>`_ project (German Indian Ocean Tsunami Early
|
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|
|
Warning System) additional functionality were implemented to fulfill the
|
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|
|
requirements of 24/7 early warning control centers. Major changes in the
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|
|
architecture of SeisComP were necessary and many new features result in
|
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|
|
the upgrade of SeisComP to version 3. Important SeisComP releases are
|
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|
|
shown below. A first prototype of :term:`SeisComP3` developed by the
|
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|
|
GITEWS/GEOFON development group was released in May 2007.
|
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SeisComP3
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|
|
A previous version of :term:`SeisComP`.
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|
seismic array
|
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|
|
An ordered arrangement of seismometers with central data acquisition specially
|
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|
|
designed to analyze seismic signal based on coherent phases. A seismic array
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|
|
differs from a local network of seismic stations mainly by the techniques
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|
|
used for data analysis. Often, a seismic array are referred to as :term:`array`.
|
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|
seismic gap
|
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|
|
A section of a fault that has produced earthquakes in the past but is now quiet.
|
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|
|
For some seismic gaps, no earthquakes have been observed historically, but it is
|
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|
|
believed (based on some other methods, such as plate-motion information, strain
|
|
|
|
|
measurements or geological observations) that the fault segment is capable of
|
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|
|
producing earthquakes. A long-term seismic gap may give hint to the most probable
|
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|
|
location of a strong earthquake in the future.
|
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|
seismic moment (M\ :sub:`0`)
|
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|
|
The seismic moment is defined as
|
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|
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|
|
.. math::
|
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|
|
M_0 = \mu D A
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|
|
with μ as rigidity of the rock at the fault, D as averaged displacement on the
|
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|
|
fault and A as fault surface area. For pure shear sources, M\ :sub:`0` equals
|
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|
|
the :term:`total seismic moment (MT)`.
|
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|
|
The seismic moment can be related to the released seismic energy ES that is
|
|
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|
|
proportional to the stress drop Δσ:
|
|
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|
|
|
|
|
|
|
.. math::
|
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|
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|
|
E_S \approx 0.5 \Delta\sigma D A
|
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|
|
Rearranging both equations yields to:
|
|
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|
|
|
|
|
|
|
.. math::
|
|
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|
|
|
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|
|
E_S \approx \frac{\Delta\sigma}{2\mu} M_0
|
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|
|
M\ :sub:`0` can be determined by the asymptote of the amplitude spectrum at
|
|
|
|
|
frequency = 0.
|
|
|
|
|
A common technique for determination of the seismic moment M\ :sub:`0` is the
|
|
|
|
|
moment tensor inversion. Assuming reasonable values for the rigidity of the
|
|
|
|
|
rock (3-6 x 104 MPa in crust and upper mantle) and the stress drop (2-6 MPa)
|
|
|
|
|
the seismic moment can be related to the surface wave magnitude Ms by the
|
|
|
|
|
empirical relationship found by :cite:t:`gutenberg-1956` (units in cgs):
|
|
|
|
|
|
|
|
|
|
.. math::
|
|
|
|
|
|
|
|
|
|
\log E_S = 11.8 + 1.5 Ms
|
|
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|
|
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|
|
|
\log M_0 = 1.5 Ms + 16.1
|
|
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|
|
seismic network
|
|
|
|
|
Group of seismic stations that are deployed as single stations or arrays.
|
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|
|
seismic ray
|
|
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|
|
Vector perpendicular to the wave front pointing into the direction of wave
|
|
|
|
|
propagation and marking behind it the "ray trace". The propagation of seismic
|
|
|
|
|
waves can be easily modelled as the propagation of seismic rays following
|
|
|
|
|
Snell's Law. This assumption is a reasonable approximation for high frequency waves.
|
|
|
|
|
|
|
|
|
|
seismic signal
|
|
|
|
|
A coherent transient waveform radiated from a definite, localized seismic source
|
|
|
|
|
that is usually considered as an useful signal for the location of the source,
|
|
|
|
|
the analysis of the source process and/or of the propagation medium (in contrast to noise).
|
|
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|
|
|
|
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|
|
seismic source
|
|
|
|
|
A localized area or volume generating coherent, usually transient seismic waveforms,
|
|
|
|
|
such as an earthquake, explosion, vibrator etc.
|
|
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|
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|
|
|
semblance
|
|
|
|
|
Normalized :term:`beam power`.
|
|
|
|
|
|
|
|
|
|
signal-to-noise ratio
|
|
|
|
|
The comparison between the amplitude of the seismic signal and the amplitude of
|
|
|
|
|
the noise; abbreviated as :term:`SNR`.
|
|
|
|
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|
|
slab
|
|
|
|
|
Usually, the part of the :term:`lithospheric <lithosphere>`
|
|
|
|
|
plate that is underthrusting in a subduction zone and is
|
|
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|
|
consumed by the Earth's mantle is called slab.
|
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|
|
|
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|
|
slab pull
|
|
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|
|
The force of gravity causing the cooler and denser oceanic :term:`slab` to sink
|
|
|
|
|
into the
|
|
|
|
|
hotter and less dense mantle material. The downdip component of this force leads
|
|
|
|
|
to downdip extensional stress in the slab and may produce earthquakes within the
|
|
|
|
|
subducted slab. Slab pull may also contribute to stress on the subduction thrust
|
|
|
|
|
fault if the fault is locked.
|
|
|
|
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|
|
slip
|
|
|
|
|
The relative displacement of formerly adjacent points on opposite sides of a fault.
|
|
|
|
|
|
|
|
|
|
slip model
|
|
|
|
|
A kinematic model that describes the amount, distribution, and timing of a slip
|
|
|
|
|
associated with an earthquake.
|
|
|
|
|
|
|
|
|
|
slip rate
|
|
|
|
|
How fast the two sides of a fault are slipping relative to one another, as
|
|
|
|
|
derived from seismic records in case of an earthquake or determined, as a
|
|
|
|
|
long-term average, from geodetic measurements, from offset man-made structures,
|
|
|
|
|
or from offset geologic features whose age can be estimated. It is measured
|
|
|
|
|
parallel to the predominant slip direction or estimated from the vertical or
|
|
|
|
|
horizontal offset of geologic markers.
|
|
|
|
|
|
|
|
|
|
slowness
|
|
|
|
|
The inverse of velocity, given in the unit seconds/degree or s/km; a large
|
|
|
|
|
slowness corresponds to a low velocity.
|
|
|
|
|
|
|
|
|
|
SNR
|
|
|
|
|
Abbreviation for :term:`signal-to-noise ratio`.
|
|
|
|
|
|
|
|
|
|
source depth
|
|
|
|
|
Location of an earthquake below the Earth's surface. Earthquakes can occur
|
|
|
|
|
between the surface and depths of about 700 km. Usually three classes of
|
|
|
|
|
earthquakes are separated according to the depth: Shallow earthquakes occur
|
|
|
|
|
in the depth range of 0 to 70 km; intermediate earthquakes between 70 and 300km
|
|
|
|
|
depth; and deep earthquakes between 300 and 700 km depth. Earthquakes at large
|
|
|
|
|
depths occur much less frequent than shallow earthquakes. Additionally, deep
|
|
|
|
|
earthquakes excite small surface waves compared to the body waves and relatively
|
|
|
|
|
simple P and S waveforms with more impulsive onsets. A more reliable way to
|
|
|
|
|
determine the depth of an earthquake is to identify depth phases (e.g. pP, sP)
|
|
|
|
|
in the waveforms. At stations with large distance to the epicenter the pP wave
|
|
|
|
|
follows the direct P wave by a time interval that slightly increases with distance
|
|
|
|
|
but rapidly with depth. The depth can be derived from this time interval by using
|
|
|
|
|
:term:`travel-time curves <travel-time curve>`.
|
|
|
|
|
|
|
|
|
|
source time function
|
|
|
|
|
The source time function describes the ground motion generated at the fault over
|
|
|
|
|
time. The function is predicted by a theoretical model.
|
|
|
|
|
|
|
|
|
|
Spooler
|
|
|
|
|
Application which watches a directory for new bulletins and performs the
|
|
|
|
|
final and service specific dissemination operation. This may involve
|
|
|
|
|
talking to modem (for fax, SMS), connecting to a SMTP server (email) or
|
|
|
|
|
rendering a Web page.
|
|
|
|
|
|
|
|
|
|
station
|
|
|
|
|
Site of measurement typically consisting of one or more sensors and one or
|
|
|
|
|
more dataloggers.
|
|
|
|
|
|
|
|
|
|
station magnitude
|
|
|
|
|
#. The station magnitude is the magnitude value based on the amplitude measurements of a single station.
|
|
|
|
|
Due to radiation pattern, site and path effects and the calibration of the station the station magnitudes
|
|
|
|
|
of one event can scatter significantly.
|
|
|
|
|
#. QuakeML object
|
|
|
|
|
|
|
|
|
|
stick-slip
|
|
|
|
|
The rapid displacement that occurs between two sides of a fault when the shear stress
|
|
|
|
|
on the fault exceeds the frictional stress. Also a jerky, sliding type of motion
|
|
|
|
|
associated with fault movement in laboratory experiments. It may be a mechanism
|
|
|
|
|
in shallow earthquakes. Stick -slip displacement on a fault radiates energy in the
|
|
|
|
|
form of seismic waves.
|
|
|
|
|
|
|
|
|
|
stress drop
|
|
|
|
|
The difference between the stress across a fault before and after an earthquake.
|
|
|
|
|
A parameter in many models of the earthquake source that affects the level of
|
|
|
|
|
high-frequency shaking radiated by the earthquake. Commonly stated in units termed
|
|
|
|
|
bars or megapascals (1 bar equals 1 kg/cm², and 1 megapascal equals 10 bars).
|
|
|
|
|
|
|
|
|
|
T
|
|
|
|
|
period, time duration
|
|
|
|
|
|
|
|
|
|
takeoff angle
|
|
|
|
|
The angle that a seismic ray makes with a downward vertical axis through the
|
|
|
|
|
source. Rays with takeoff angles less than 90° are labeled with capital letters
|
|
|
|
|
like P or S. If the takeoff angle is greater than 90° the ray is upgoing and is
|
|
|
|
|
labeled with lowercase letters (p or s). Such rays can be reflected at the
|
|
|
|
|
surface near the epicenter forming a depth phase (see :term:`pP phase` or :term:`sP phase`).
|
|
|
|
|
|
|
|
|
|
teleseismic
|
|
|
|
|
Pertaining to a seismic source at distances greater than about 2000 km from the
|
|
|
|
|
measurement site.
|
|
|
|
|
|
|
|
|
|
theoretical onset
|
|
|
|
|
The point where an arrival is expected to appear on a seismic record, based
|
|
|
|
|
on the known location and depth of the seismic source and according to a velocity
|
|
|
|
|
model.
|
|
|
|
|
|
|
|
|
|
time domain
|
|
|
|
|
A seismic record is usually presented in the time domain, i.e., as a display of
|
|
|
|
|
varying amplitudes of (filtered) ground motion as a function of time (in contrast
|
|
|
|
|
to the equivalent representation in the frequency domain) (see also Fourier analysis).
|
|
|
|
|
|
|
|
|
|
Tp
|
|
|
|
|
predominant period
|
|
|
|
|
|
|
|
|
|
Tm
|
|
|
|
|
mean period
|
|
|
|
|
|
|
|
|
|
total seismic moment (MT)
|
|
|
|
|
A measure of the strength of the full :term:`moment tensor`:
|
|
|
|
|
|
|
|
|
|
.. math::
|
|
|
|
|
|
|
|
|
|
M_T = \sqrt{\sum_{ij}M_{ij}M_{ij}/2}
|
|
|
|
|
|
|
|
|
|
For pure shear sources M\ :sub:`T` equals :term:`seismic moment (M0)`.
|
|
|
|
|
|
|
|
|
|
transfer function
|
|
|
|
|
The transfer function of a seismic sensor-recorder system (or of the Earth
|
|
|
|
|
medium through which seismic waves propagate) describes the frequency-dependent
|
|
|
|
|
amplification, damping and phase distortion of seismic signals by a specific
|
|
|
|
|
sensor-recorder (or medium). The modulus (real term = absolute value) of the
|
|
|
|
|
transfer function is termed the frequency response function or magnification
|
|
|
|
|
curve, e.g. of a seismograph.
|
|
|
|
|
|
|
|
|
|
travel time
|
|
|
|
|
The time required for a wave traveling from its source to a point of observation.
|
|
|
|
|
|
|
|
|
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travel-time curve
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A graph of arrival times, commonly of direct as well as multiply reflected and
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converted :term:`P<P wave>` or :term:`S waves<S wave>`, recorded at different
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points as a function of distance
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from the seismic source. Seismic velocities within the Earth can be computed
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from the slopes of the resulting curves.
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XXL event
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An event based on :term:`XXL picks<XXL pick>`.
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XXL pick
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Picks that have extraordinarily large amplitudes and large :term:`SNR<SNR>` and
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that lie within a relatively small region.
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vespagram
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Vespagrams are diagrams of :term:`beam` traces over time typically formed
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for a particular :term:`azimuth` (or :term:`backazimuth`) and for
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ranges of :term:`slowness` (slowness vespagram). When the slowness
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is kept constant and the backazimuth is varied the term backazimuth
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vespagram is used.
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Wadati-Benioff zone
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A dipping planar (flat) zone of earthquakes that is produced by the interaction
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of a downgoing oceanic crustal plate with a continental plate. These earthquakes
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can be produced by slip along the subduction thrust fault (thrust interface between
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the continental and the oceanic plate) or by slip on faults within the downgoing
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plate as a result of bending and extension as the plate is pulled into the mantle.
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Slip may also initiate between adjacent segments of downgoing plates. Wadati-Benioff
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zones are usually well-developed along the trenches of the Circum-Pacific belt,
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dipping towards the continents.
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wave number
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Number of cycles of a repeating signal per unit length, typically per meter of kilometer.
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P wave
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P (primary) waves are compressional waves involving volumetric variations in the
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media. The sense of particle motion is linear and parallel to the propagation
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direction. P waves are body waves that traverse the interior of a body/Earth and
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can propagate in fluids.
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The general nomenclature for P waves: At local and
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regional distances a special nomenclature is used to describe the travel path of
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the first P and S arrivals. Pg, Pb/P* and Pn phases are separated. Pg is the direct
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P wave arriving first in distances less than around 100 km. Pn is the head wave
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along the Moho arriving first at larger distances than 100 km (depending on the
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crustal thickness). Pn has usually smaller amplitudes than Pg. Pb or P* is the
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rarely observed head wave travelling along the midcrustal velocity discontinuity.
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The general nomenclature of P waves entitles reflections at the topside of boundaries
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with lowercase letters (m – Moho reflection; c - CMB reflection; i - inner core-outer
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core boundary reflection), e.g. PmP is a reflected P wave at the Moho. Reflections
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at the bottom side of boundaries get no additional letter, e.g. PP is a reflected
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P wave at the Earth's surface. Refracted rays get capital letters (K - through
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the outer core; I - through the inner core), e.g. PKIKP is a P wave traversing
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the crust/mantle, the outer core, the inner core, again the outer core and again
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the mantle/crust.
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S wave
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S (secondary) waves are shear waves without any volumetric variation in the media.
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The sense of particle motion is perpendicular to the propagation direction. S waves
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are body waves that traverse the interior of a body but can not propagate in fluids.
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Analog to the P arrivals Sg, Sb/S\ :sup:`*` and Sn arrivals are distinguished in local
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and regional distances. The general nomenclature of S waves is analog to the P waves.
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The reflections at the topside of boundaries have lowercase letters (m - Moho
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reflection; c - CMB reflection), e.g. SmS is a reflected S wave at the Moho.
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Reflections at the bottom side of boundaries get no additional letter, e.g. SS is a
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reflected S wave at the Earth's surface. Refracted rays get capital letters (J - through
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the inner core), e.g. SKJKS is a S wave traversing the crust/mantle, the outer core
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as a :term:`P wave`, the inner core as a :term:`S wave`, again the outer core as a P wave and again
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the mantle/crust as S wave. S waves can not travel through the outer core because
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the outer core consists of a fluid.
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surface wave
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Surface waves are seismic waves observed only at the free surface of the media.
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Two types of surface waves are distinguished: :term:`Love waves<Love wave>` (L)
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and :term:`Rayleigh waves<Rayleigh wave>` (R).
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Both result from the interaction of P and S waves near the free surface.
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waveform (data)
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The complete analog or sufficiently dense sampled digital representation of a
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continuous wave group (e.g., of a seismic phase) or of a whole wave train
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(seismogram). Accordingly, waveform data allow to reconstruct and analyze the
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whole seismic phase or earthquake record both in the time and frequency domain
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whereas parameter data describe the signal only by a very limited number of more
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or less representative measurements such as onset time, maximum signal amplitude
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and related period.
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waveformID
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Attribute of the QuakeML objects Pick, !StationAmplitude and !StationMagnitude
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describing the source of the underlying waveform source. The WaveformID contains
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information about the !NetworkCode, !StationCode, !LocationCode and !ChannelCode
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wave front
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The surface formed by all elements of a propagating wave, which swing in phase;
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the wave front is perpendicular to the seismic rays, which are oriented in
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direction of wave propagation.
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wavelength
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The distance between successive points of equal amplitude and phase on a
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wave (for example, crest to crest or trough to trough).
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weight
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Attribute of the QuakeML objects Arrival and !MagnitudeReferences defining the
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effect of the referenced object (e.g. Pick).
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WWSSN_SP
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Short period seismograph with a dominant period of 1 s of the World-Wide
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Standard Seismograph Network (WWSSN).
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WWSSN_LP
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Long period seismograph with a dominant period of 20 s of the World-Wide
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Standard Seismograph Network (WWSSN).
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XML
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Extensible Markup Language
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