.. _glossary:

********
Glossary
********

The glossary is partly extracted from New Manual of Observatory Practice and some information
is taken from Modern Global Seismology.


|scname| terms
==============

.. glossary::

   binding
      A binding is a set of configuration options to configure the connection between a
      :term:`module` and a station. Bindings are located in ``etc/key/modulename/station_NET_STA``.
      They are either written to the database or used to create native configuration files
      for standalone modules. The concepts section on :ref:`configuration <concepts_configuration>`
      provides more details.

   module
      A module is usually a binary executable that does a certain job such as :ref:`seedlink`
      or :ref:`scautopick`. The concepts section on :ref:`modules <concepts_modules>`
      provides more details.

   plugin
      An extension to a module. The concepts section on :ref:`plugins <concepts_plugins>`
      provides more details.

   profile
      A profile is a special :term:`binding`. Instead of defining the same set of configuration
      options again and again for many stations a profile can be used. Instead of configuring a
      stations like:

      .. code-block:: sh

         seedlink
         scautopick

      which refers to ``etc/key/seedlink/station_NET_STA`` and ``etc/key/scautopick/station_NET_STA``
      a profile can be given:

      .. code-block:: sh

         seedlink:geofon
         scautopick:teleseismic

      which refers to :file:`etc/key/seedlink/profile_geofon` and
      :file:`etc/key/scautopick/profile_teleseismic`.
      Changing the profile changes the bindings of all stations that use this profile.

   RecordStream
       Interface to access data records from data processing modules.
       :term:`SeisComP` applications access waveform data through the
       :ref:`RecordStream interface <concepts_RecordStream>`.

   standalone module

      A module that needs to convert the configuration or do not use the default
      configuration options (see below) is called a standalone modules.
      Examples for standalone modules are :ref:`seedlink`, :ref:`slarchive` or :ref:`slmon`.

   trunk
      The module and library collection which forms and uses the SeisComP
      framework. The Application class is part of this framework. All trunk
      modules share a common configuration schema and a database with
      Inventory, EventParameters, Configuration, Routing and QC schemas.
      Representatives are :ref:`scautoloc` and :ref:`scautopick` and the GUI
      collection with :ref:`scolv`, :ref:`scmv`, :ref:`scrttv` and :ref:`scesv`.

----


Scientific and technical terms
==============================

.. glossary::

   AIC
      Aikaike Information Criterion used for refinement of phase picks.
      Phase pickers for picking P and S phase arrivals based on AIC may reach
      high accuracy if tuned well.

   aftershocks
      Earthquakes that follow a large earthquake in a sequence. They are smaller than the mainshock
      and within 1-2 fault lengths distance from the mainshock fault. Aftershocks can continue over
      a period of weeks, months, or years, decreasing in frequency with time. In general, the larger
      the mainshock, the larger and more numerous the aftershocks, and the longer they will continue.

   amplitude
      #. General term used for an observation of a wave at a particular time.
      #. QuakeML object. Amplitudes are computed, e.g. for computing
         :term:`magnitudes <magnitude>` of different types. Another type is the
         :term:`SNR`. Amplitude computation depends on the type.

      In |scname| amplitudes are computed automatically by :ref:`scautopick` and
      :ref:`scamp` or interactively by :ref:`scolv`.

   array
      A set of observing sensors at which the observed and sought signal are mostly coherent.
      If the sensors are seismometers or barometers measuring infrasound, the terms
      :term:`seismic array` or :term:`infrasound array` are used, respectively.
      Arrays are different from a :term:`network` by the applied methods, e.g.
      :term:`F-K` analysis, :term:`beam` forming or :term:`vespagram` analysis.

   ATF
      The :term:`array transfer function` or :term:`array response function`
      describes the sensitivity and resolution of an :term:`array` to signals
      propagating through the array with a particular :term:`azimuth`, :term:`slowness`
      and :term:`frequency`.

   array response function
      A synonym of :term:`ATF` or :term:`array transfer function`.

   array transfer function
      A synonym of :term:`ATF` or :term:`array response function`.

   ArcLink
      ArcLink complements :term:`SeedLink` by providing access to archived waveform
      data. Arclink was distributed with :term:`SeisComP` until version 3.0.

   arrival
      #. The appearance of seismic energy on a seismic record
      #. QuakeML object. The detected phase onset associated to an origin in |scname|.

   arrival time
      The time at which a particular phase of a seismic wave arrives at a station.

   asthenosphere
      The ductile part of the Earth, just below the brittle :term:`lithosphere`,
      in the upper mantle. The lithosphere/asthenosphere reaches down to about 200 km.

   azimuth
      In general a direction measured clock-wise in degrees against north. In seismology used to
      measure the direction from a seismic source to a seismic station recording this event.

   beam
      The sum of signals observed at an :term:`array` shifted with respect
      to the array reference coordinate assuming a particular :term:`slowness`
      and :term:`azimuth`. Optimum values for slowness and azimuth can be
      found, e.g. by :term:`F-K` analysis.

   beam packing
      Equivalent to the :term:`F-K` analysis where the :term:`beam` and the related
      parameters such as :term:`beam power` or :term:`semblance` are formed in the
      time domain. Seismograms from the :term:`array` stations are shifted according
      to the considered ranges of :term:`slowness` and :term:`backazimuth` or
      :term:`wave number` and summed to form the beam.

   beam power
      The energy of :term:`beam` within a defined time window.

   backazimuth
      The direction from the seismic station towards a seismic source, measured in degrees clock-wise
      against north; sometimes also just called azimuth.

   Benioff zone
      see :term:`Wadati-Benioff zone`

   body wave
      A seismic wave that propagates through the interior of the Earth, as opposed to
      surface waves that propagate near the Earth's surface. :term:`P<P wave>` and :term:`S waves<S wave>`, which shake
      the ground in different ways, are examples.

   body wave magnitude
      see :term:`magnitude, body-wave (mb)`

   calibration
      The process of determining the response function (distortion of the input signal) and
      sensitivity of an instrument or its derived component.

   CAV
      cumulated absolute velocity

   CI
      Characteristic Intensity

   channel code
      Description of characteristics of data related to the recording sensor and
      data logger as well as instrument responses, sampling frequencies, etc.
      The standard codes are defined in the :cite:t:`seed-2012`.

   Circum-Pacific belt
      The zone surrounding the Pacific Ocean that is characterized by frequent and strong
      earthquakes and many volcanoes as well as high tsunami hazard. Also called the Ring of Fire.

   coda
      The tail of a seismic signal, usually with exponentially decaying amplitudes, which
      follow a strong wave arrival. Coda waves are due to scattering and superposition of multi-path arrivals.

   coda phase
      A detection of a single phase of unknown path found within the coda signal envelope,
      designated as tx, e.g. Px or Sx.

   coherent
      Seismic signals detected on various seismic sensors of a seismic array or network are said to
      be coherent if they are related to each other in time, amplitude and/or waveform because they
      come from the same seismic source.

   color
      Colors are given in hexadecimal representation or by :term:`color keyword names <color keyword name>`.

   color keyword name
      Color keyword names allow the specification of color values by names
      representing color codes instead of RGB or hexadecimal representation. Find examples
      on the `website of W3C <https://www.w3.org/TR/SVG11/types.html#ColorKeywords>`_.
      Color keyword names have been introduced in SeisComP in version 4.4.0.

   convolution
      A mathematically equivalent operation that describes the action of a linear (mechanical
      and/or electronic) system on a signal, such as that of a filter on a seismic signal.

   core
      The innermost part of the Earth. The outer core extends from about 2900 to about 5120 km below
      the Earth's surface and consists in its main components of a mixture of liquid iron and nickel.
      The inner core is the central sphere of the Earth with a diameter of 1250 km and consists of solid metal.

   Core-Mantle Boundary(CMB)
      see :term:`Gutenberg discontinuity`

   corner frequency
      The frequency at which the curve representing the Fourier amplitude spectrum of a recorded seismic
      signal abruptly changes its slope. For earthquakes, this frequency is a property of the source and
      related to fault size, rupture velocity, source duration and stress drop in the source. Also the
      frequency at which the transfer function / magnification curve of a recording system changes its slope.

   creep
      Slow, more or less continuous movement occurring on faults due to ongoing tectonic deformation.
      Also applied to slow movement of landslide masses down a slope because of gravitational forces.
      Faults that are creeping do not tend to have large earthquakes. This fault condition is commonly
      referred to as unlocked.

   crust
      The outermost major layer of the Earth, ranging from about 10 to 70 km in thickness worldwide.
      The oceanic crust is thinner (about 10 to 15 km) than the continental crust (about 25 to 70 km).
      The uppermost 15-35 km of the crust is brittle enough to produce earthquakes. The seismogenic crust
      is separated from the lower crust by the brittle-ductile boundary. The crust is usually characterized
      by P-wave velocities below 8 km/s (average velocity of about 6 km/s).

   delay
      The time difference between the arrival time and the end time of the last record achieved plus
      the half record length. The delay can be computed by :ref:`scqc`.

   depth Phase
      see :term:`pP phase` or :term:`sP phase`

   detection
      Identification of an arrival of a seismic signal with amplitudes above and/or signal shape
      (waveform) different from seismic noise.

   directivity
      An effect of a propagating fault rupture whereby the amplitudes of the generated ground motions
      depend on the direction of wave propagation with respect to fault orientation and slip
      direction (radiation pattern). The directivity and thus the radiation pattern is different for
      :term:`P<P wave>` and :term:`S waves<S wave>`.

   EDA
      Effective Design Acceleration

   EIDA
      European Integrated Data Archive: http://www.orfeus-eu.org/data/eida/

   epicenter
      Vertical projection of the hypocenter to the surface.

   event
      #. General term used for a localized disturbance (earthquake, explosion, etc.) which generates seismic waves.
      #. QuakeML object. The event is the parent object of several :term:`origins <origin>`.
         Among these origins a preferred origin
         and its :term:`preferred magnitude` is selected to represent the event.
         An event can be seen as an earthquake folder
         which contains information about earthquake parameters.

   fault-plane solution
      Representation of the fault activated in an earthquake and the caused direction of slip on the fault by
      a circle with two intersecting curves looking like a beach ball. A fault-plane solution is found by the
      analysis of seismic records at many stations of an earthquake to obtain the radiation pattern. From the
      radiation pattern the fault parameter and the slip direction are determined using a stereographic
      projection or its mathematical equivalent. The most common analysis uses the direction of first motion
      of P wave onsets and yields two possible orientations for the fault rupture and the direction of seismic
      slip. Another technique is to use the polarization of teleseismic :term:`S waves<S wave>` and/or to measure amplitude
      ratios between different phase types. Further inferences can be made from these data concerning the
      principal axes of stress in the region of the earthquake. The principal stress axes determined by this
      method are the compressional axis (also called the P-axis, i.e. the axis of greatest compression, or s1),
      the tensional axis (also known as the T-axis, i.e., the axis of least compression, or s3), and the
      intermediate axis (s2).

   filter(ing)
      A filter attenuates certain frequencies of a (seismic) signal and amplifies others. The process of
      filtering can be accomplished electronically while recording or numerically in a computer. Filtering also
      occurs naturally as seismic energy passes through the Earth.

      The available and integrated filters in |scname| are documented in :ref:`filter-grammar`.

   first motion
      The first noticeable displacement in a seismogram caused by the arrival of a P wave at the seismometer.
      Upward motion of the ground at the seismometer indicates a dilatation at the source, downward motion
      indicates a compression. Due to the presence of seismic noise the proper polarity of the first motion
      may be difficult to recognize.

   F-K
      F-K refers to a 2-D :term:`Fourier analysis` where the base functions
      are defined, e.g. by ranges of :term:`frequency` and :term:`wave number`.
      F-K analysis is applied for signal detection by transforming time series
      recorded at several sensors, e.g. seismic or infrasound :term:`array`
      stations to the time and space domain.

      The equivalent to F-K analysis in the time domain is :term:`beam packing`.

   focal mechanism
      see :term:`fault-plane solution`

   foreshocks
      Earthquakes that occur in a series of earthquakes before the largest earthquake, termed the mainshock.
      Foreshocks may precede the mainshock by seconds to weeks and usually originate at or near the focus
      of the larger earthquake. Not all mainshocks have foreshocks.

   Fourier spectrum
      The relative amplitudes (and phase angles) at different frequencies that are derived from a time series
      by Fourier analysis.

   Fourier analysis
      The mathematical operation that resolves a time series (for example, a recording of ground motion)
      into a series of numbers that characterize the relative amplitude and phase components of the signal
      as a function of frequency.

   frequency
      Number of cycles of a repeating signal per unit time, typically per second.

   frequency domain
      The transformation of a seismic signal from the time domain (as a seismogram) to the frequency
      domain is conducted by a :term:`Fourier analysis`. The signal is represented in the frequency domain by
      the amplitude and phase components as a function of frequency (see spectrum). The representations of
      a seismic signal in the time and in the frequency domain are equivalent in a mathematical sense.
      For some procedures of data analysis the time-domain representation of a seismic record is more
      suitable while for others the frequency-domain approach is more appropriate and efficient.

   gempa GmbH
      `gempa GmbH <http://www.gempa.de/>`_ is a spin-off from :term:`GFZ`
      offering a range of services and products to monitor, process and analyze
      seismicity. It is the main development and service company for |scname|.

   GEOFON
      GEOFON (https://geofon.gfz-potsdam.de) is part of the Modular Earth Science
      Infrastructure (MESI) at :term:`GFZ`.

   geometrical spreading
      The component of reduction in wave amplitude due to the radial spreading of seismic energy with
      increasing distance from a given source.

   GFZ
      Helmholtz Centre Potsdam `German Research Centre for Geosciences <http://www.gfz-potsdam.de/>`_.
      |scname| was originally developed at GFZ.

   GMPE
      Ground Motion Prediction Equation

   Green's function
      A mathematical representation that, in reference to earthquake shaking, is used to represent the
      ground motion caused by instantaneous slip on a small part of a fault. Green’s functions can be
      summed over a large fault surface to compute the ground shaking for a large earthquake rupturing
      a fault of finite size. The fractional fault-slip events that are summed can be records from
      small earthquakes on the fault or they can be theoretically computed small-earthquake records.

   Gutenberg discontinuity
      The seismic velocity discontinuity marking the core-mantle boundary (CMB) at which the velocity
      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
      about 7.3 km/s to 0 km/s. The CMB reflects the change from the solid mantle material to the
      fluid outer core.

   GUI

      Graphical use interface, e.g. :ref:`scolv`.

   hypocenter
      Coordinates of an earthquake point source. Hypocenters based on :term:`P<P wave>` and :term:`S wave`
      first arrivals point to the place where the rupture process starts. For large earthquakes the
      source location determined by :term:`P wave` first arrivals can differ significantly from the location of
      maximum energy release.

   Ia
      Arias Intensity

   infrasound array
      An :term:`array` of barometers measuring infrasound signals.

   intensity
      A measure of the effects of an earthquake at a particular place at the Earth's surface on humans
      and (or) structures. The intensity at a point depends not only upon the strength of the earthquake
      (magnitude) but also upon the distance from the earthquake, the depth of the hypocenter and the
      local geology at that point. Several scales exist, most of them giving the intensity in 12 degrees,
      usually written as Roman numerals. Most frequently used are at present the European Macroseismic
      Scale (EMS-98), and in the United States the Modified Mercalli scale and the Rossi-Forel scale.
      There are many different intensity values for one earthquake, depending on how far you are away
      from the epicenter; this is unlike the magnitude value, which is one number for each earthquake
      as a measure of the amount of seismic wave energy released by it.

   interplate/intraplate
      Intraplate pertains to processes within the Earth's crustal plates. Interplate pertains to
      processes between the plates.

   interplate coupling
      The qualitative ability of a subduction thrust fault to lock and accumulate stress. Strong
      interplate coupling implies that the fault is locked and capable of accumulation stress whereas
      weak coupling implies that the fault is unlocked or only capable of accumulating low stress.
      A fault with weak interplate coupling could be aseismic or could slip by creep.

   inventory
      The inventory is the collection of all available meta data related to :term:`network`,
      :term:`station`, :term:`location code`, station :term:`channel code`,
      characteristics of sensors and data loggers, etc. More details are given in
      the concepts section :ref:`concepts_inventory`.

   latency
      Time difference between the end times of consecutive records.
      The latency can be computed by :ref:`scqc`.

   lithosphere
      The outer solid part of the Earth, including crust and uppermost mantle. The lithosphere is
      about 100 km thick, although its thickness is age-dependent (older lithosphere is thicker).
      At some locations the lithosphere below the crust is brittle enough to produce earthquakes by
      faulting, such as within a subducted oceanic plate.

   location code
      Description of particular sensor location associated to a station. The standard
      location codes are defined in the :cite:t:`seed-2012`.

   Love wave
      A major type of surface waves having a horizontal motion that is transverse (or perpendicular)
      to the direction of propagation. It is named after A. E. H. Love, the English mathematician
      who discovered it.

   leaky mode
      A seismic surface wave which is imperfectly trapped, e.g., within a low-velocity layer or a
      sequence of layers, so that its energy leaks or escapes across a layer boundary causing some
      attenuation.

   low-velocity layer/zone
      Any layer in the Earth in which seismic wave velocities are lower than in the layers above and below.

   magnification curve
      A diagram showing the dependence of amplification, e.g. of the seismic ground motion by a
      seismograph, as a function of frequency.

   magnitude
      A number that characterizes the relative size of an earthquake. The magnitude is based on
      :term:`amplitude` measurement of the maximum motion recorded by a seismograph
      (sometimes for waves of a particular frequency),
      corrected for the attenuation with distance. Several scales have been defined, but the most commonly used are:

      #. local magnitude (ML), commonly referred to as "Richter magnitude"
      #. surface-wave magnitude (Ms)
      #. body-wave magnitude (mb)
      #. moment magnitude (Mw).

      The magnitude scales 1-3 have limited range and applicability and do not
      satisfactorily measure the
      size of the largest earthquakes. The moment magnitude (Mw) scale, based on
      the concept of seismic moment,
      is uniformly applicable to all earthquake sizes but is more difficult to
      compute than the other types. In
      principal, all magnitude scales could be cross calibrated to yield the same
      value for any given earthquake, but
      this expectation has proven to be only approximately true, thus the
      magnitude type as well as its value is needed to be specified.

      Additional or modified magnitudes can be computed by providing plugins.

      In |scname| magnitudes are computed automatically by :ref:`scmag` or interactively
      by :ref:`scolv`.

   magnitude, local (ML)
      Magnitude scale introduced by Richter in the early 1930s (:cite:t:`richter-1935`)
      to have a common scale for the strength of earthquakes. The basic observation
      is the systematic decay of the logarithm of the maximum
      amplitudes with increasing distance for different earthquakes described by:

      .. math::

         ML = \log A_{max} - \log A_0

      with A\ :sub:`0` as amplitude of a reference event. For the reference event
      ML = 0 the formula can be rewritten to

      .. math::

         ML = \log A_{max} - 2.48 + 2.76 \log \Delta

      with Δ being the distance of the station to the earthquake location. ML is a
      magnitude scale for
      recordings of earthquakes smaller than ML 7 at regional stations. It is
      usually a measure of the
      regional-distance S-wave on horizontal component records.
      The original formula is only valid for records from a :term:`Wood-Anderson torsion
      seismometer <Wood-Anderson seismometer>` with a natural period of
      0.8 s and shallow earthquakes in California. Therefore calibration functions
      for other regions and wider depth ranges are necessary.
      A :term:`Wood-Anderson torsion seismometer <Wood-Anderson seismometer>` is
      simulated when measuring amplitudes.

      For amplitudes measured on the vertical component records, additional
      correction factors have to be applied. ML saturates at
      magnitudes around 7 because the maximum amplitudes of larger earthquakes
      occur at longer periods than
      the bandpass of 0.1 s and 3 s for the magnitude calculation.

      In |scname| a modified local magnitude
      :term:`MLv <magnitude, local vertical (MLv)>` is determined by simulation
      of a Wood-Anderson instrument and then measuring the amplitude in a 150 s
      time window on the vertical component of station with distances smaller than 8°.

      * Amplitude unit in |scname|: **millimeter** (mm)

      Read the :ref:`technical documentation <global_ml>` for more details and
      the configuration.

   magnitude, local custom (MLc)
      The local magnitude measured on the horizontal components with
      custom parametric or non-parametric function, configurable amplitude
      filtering, :term:`Wood-Anderson torsion seismometer <Wood-Anderson
      seismometer>` and distance measures.

      * Amplitude unit in |scname|: **millimeter** (mm)

      Read the :ref:`technical documentation <global_mlc>` for more details and
      the configuration.

   magnitude, local horizontal (MLh)
      The local magnitude computed from amplitudes measured on the horizontal
      components with a modified parametric calibration function as compared to
      :term:`ML <magnitude, local (ML)>`.

      * Amplitude unit in |scname|: **millimeter** (mm)

      Read the :ref:`technical documentation <global_mlh>` for more details and
      the configuration.

   magnitude, local GNS/GEONET (MLr)
      Local magnitude calculated from :term:`MLv <magnitude, local vertical (MLv)>`
      amplitudes based on GNS/GEONET specifications for New Zealand.

      Read the :ref:`technical documentation <global_mlr>` for more details and the configuration.

   magnitude, local vertical (MLv)
      The :term:`ML <magnitude, local (ML)>` magnitude with amplitudes measured on
      the vertical component instead of the horizontals.

      * Amplitude unit in |scname|: **millimeter** (mm)

      Read the :ref:`technical documentation <global_mlv>` for more details and the configuration.

   magnitude, Nuttli (MN)
      Nuttli magnitude for Canada and other Cratonic regions.

      * Amplitude unit in |scname|: **meter/second** (m/s)

      Read the :ref:`technical documentation <global_mn>` for more details and the configuration.

   magnitude, body-wave (mb)
      Magnitude developed for teleseismic body waves. mb is defined on the amplitude
      of the first few cycles of the P-wave restituted to :term:`WWSSN_SP`.

      * Amplitude unit in |scname|: **nanometer** (nm)

      Read the :ref:`technical documentation <global_mb>` for more details and the configuration.

   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|.

   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)>`.

      * Amplitude unit in |scname| is **nanometer per second** (nm/s)

      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))
      Ms(BB) is a broadband magnitude scale based on teleseismic surface waves.
      In contrast to :term:`Ms <magnitude, surface wave (Ms)>`, amplitudes for Ms(BB)
      are measured as the maximum on vertical true ground motion velocity seismograms without
      instrument simulation or restitution.

      The Moscow-Prague equation for surface wave magnitude is applied as given by

      .. math::

         M_s = \log \left(\frac{A}{2\pi}\right) + 1.66 \log(\Delta) + 3.3

      * Amplitude unit in |scname|: **meter per second** (m/s)
      * Period range: all
      * Distance range: 2 - 160°
      * Depth range: 0 - 100 km
      * Time window: distance (km) / 3.5 km/s + 30 s

   magnitude, duration (Md)
      The duration magnitude measured on the coda wave train.

      Read the :ref:`technical documentation <global_md>` for more details and the configuration.

   magnitude, JMA (M_JMA)
      M(JMA) is a magnitude similar to the Ms, but the formula is calibrated for instruments
      with 5 s period at local distances. The data set for the calibration was gained by the
      Japan Meteorological Agency (JMA).

      .. math::

         M(JMA) = \log \sqrt{{A_N}^2 + {A_E}^2} + 1.73 \log\Delta - 0.83

      This equation is valid for local (< 2000 km) and shallow (< 80 km)
      earthquakes. For deeper earthquakes additional correction functions have
      to be applied (:cite:t:`katsumata-1996`).

      * Amplitude unit in |scname|: **micrometer** (um)
      * Time window: 150 s
      * Epicentral distance range: 0 - 20°
      * Depth range: 0 - 80 km

   magnitude, moment (Mw)
      The moment magnitude is a magnitude scale related to the seismic moment M\ :sub:`0` and
      thus to the released seismic energy.
      To obtain Mw the seismic moment is first determined, e.g. by a moment tensor inversion.
      Then the Mw is gained by the following standard relationship between seismic moment
      and the moment magnitude (M\ :sub:`0` in cgs units of dyn*cm):

      .. math::

         Mw = \frac{2}{3}(\log M_0 - 16.1)

      This equation is analog to the relation between M\ :sub:`s` and M\ :sub:`0`.

   magnitude, averaged moment (Mw(avg))

      Moment magnitude derived as a weighted average of other magnitudes.

   magnitude, broadband P-wave moment (Mwp)
      The Mwp is a rapid estimate of the moment magnitude based on the
      first-arrival P waves on broadband seismograph records. The displacement
      seismograms of the P wave portion are considered as source time function
      approximation. The seismic moment is estimated for each station by
      integrating the displacement records. The combination of multiple records
      results in an estimation of the moment magnitude without correction
      for the source mechanism (:cite:t:`tsuboi-1995`).

      * Amplitude unit in |scname|: **nanometer times second** (nm*s)
      * Time window: 95 s
      * Epicentral distance range: 5 - 105°

   magnitude, derived mB (Mw(mB))
      Moment magnitude derived from :term:`mB <magnitude, broadband body-wave (mB)>`
      magnitudes using linear conversion:

      Mw(mB) = 1.30 mB - 2.18

   magnitude, derived Mwp (Mw(Mwp))
      Moment magnitude derived from :term:`Mwp <magnitude, broadband P-wave moment (Mwp)>`
      magnitudes using linear conversion after :cite:t:`whitmore-2002`:

      Mw(Mwp) = 1.31 Mwp - 1.91

   magnitude, summary (M)

      Summary magnitude derived from multiple other magnitudes by :ref:`scmag`.

   mainshock
      The largest earthquake in a sequence, sometimes preceded by one or more foreshocks,
      and almost always followed by many aftershocks.

   mantle
      The part of the Earth's interior between the core and the crust.

   microearthquake
      An earthquake that is not perceptible by man and can be recorded by seismographs only.
      Typically, a microearthquake has a magnitude of 2 or less on the Richter scale.

   microseism
      #. In a broader sense: A more or less continuous motion in the Earth in a wide frequency
         range that is unrelated to any earthquake and caused by a variety of usually uncorrelated
         (incoherent) natural and artificial (man-made) sources.
      #. In a more specific sense: That part of seismic noise that is generated by wave motions
         on lakes and oceans and their interaction with shores, typically with periods between
         about 2 to 9 s (the stronger secondary microseisms), and 11 to 18 s (the weaker
         primary microseisms).

   miniSeed
      miniSEED is the
      standard for the exchange of seismic time series. It uses a fixed record
      length and applies data compression as defined in :cite:t:`seed-2012`.

   MMI
      Modified Mercalli Intensity

   Moho
      The abbreviation for the :term:`Mohorovičić discontinuity`.

   Mohorovičić discontinuity
      The discontinuity in seismic velocities that defines the boundary between crust and mantle
      of the Earth. Named after the Croatian seismologist Andrija Mohorovičič (1857-1936) who
      discovered it. The boundary is between 20 and 60 km deep beneath the continents and between
      5 and 10 km deep beneath the ocean floor.

   moment tensor

      Moment tensors or seismic moment tensors describe the equivalent forces
      due to seismic point sources, e.g. earthquakes with rupture dimensions
      much smaller than the distance at which they are observed.

   network
      A set of stations typically maintained by one or more institutions and
      tuned to record particular signals.

   network magnitude
      a. The network magnitude is a magnitude value summarizing several :term:`station magnitude` values
	 of one :term:`origin`. Read the documentation of :ref:`scmag` for the details.
      #. QuakeML object.

   noise (seismic)
      Incoherent natural or artificial perturbations caused by a diversity of agents and
      distributed sources. One usually differentiates between ambient background noise and
      instrumental noise. The former is due to natural (ocean waves, wind, rushing waters,
      animal migration, ice movement, etc.) and/or man-made sources (traffic, machinery, etc.),
      whereas instrumental (internal) noise may be due to the flicker noise of electronic
      components and/or even Brownian molecular motions in mechanical components. Digital
      data acquisition systems may add digitization noise due to their finite discrete
      resolution (least significant digit). Very sensitive seismic recordings may contain
      all these different noise components, however, usually their resolution is tuned so
      that only seismic signals and to a certain degree also the ambient noise are resolved.
      Disturbing noise can be reduced by selecting recording sites remote from noise sources,
      installation of seismic sensors underground (e.g., in boreholes, tunnels or abandoned
      mines) or by suitable filter procedures (improvement of the signal-to-noise ratio).

   Nyquist frequency
      Half of the digital sampling rate. It is the minimum number of counts per second
      needed to define unambiguously a particular frequency. If the seismic signal contains
      energy in a frequency range above the Nyquist frequency the signal distortions are
      called aliasing.

   onset
      The first appearance of a seismic signal on a record.

   origin
      #. Location (hypocenter), Time and strength estimation of an earthquake based on seismic
         phases and amplitudes
      #. QuakeML object

   origin time
      Estimated source time of an event belonging to a certain origin; describes the
      rupture start time. Attribute of the QuakeML object Origin, see :term:`origin`.

   phase
      #. A stage in periodic motion, such as wave motion or the motion of an oscillator,
         measured with respect to a given initial point and expressed in angular measure.
      #. A pulse of seismic energy arriving at a definite time, which passed the Earth
         on a specific path.
      #. Attribute of the QuakeML object Arrival, see :term:`arrival`.

   P phase
      The P phase is the arrival of the direct P wave that traveled through the Earth's
      crust and mantle observed in epicentral distances up to 100°.

   Pdiff phase
      The long-period P-wave energy can be diffracted at the CMB forming at distances larger
      than 100° the Pdiff phase. The reason for the diffraction is the large reduction of the
      P wave velocity at the CMB from about 13.7 km/s to 8 km/s. The amplitude of Pdiff is
      relatively small. Pdiff is observed at distances where the outer core forms the "core
      shadow" (see also :term:`PKP phase`).

   Pg phase
      Pg is the direct P wave arriving first in local distances less than 100 km. For larger
      distances Pn arrives first (see :term:`Pn phase` for details).

   PGA
      Peak Ground Acceleration

   PGD
      Peak Ground Displacement

   PGV
      Peak Ground Velocity

   Pn phase
      Pn is the P head wave along the Moho arriving first at local distances larger than
      100 km (depending on the crustal thickness). Pn has usually smaller amplitudes than Pg.

   PcP phase
      The P wave that is reflected at the CMB forms the PcP. At epicentral distances between
      30° and 55° PcP is often recorded as sharp pulse.

   PKiKP phase
      A P wave that travels through the Earth's crust and mantle and is reflected at the
      outer core-inner core boundary. At distances between 100° and 113° PKiKP can be the
      first arrival if no Pdiff is observed.

   PKP phase
      The direct P waves traversing the Earth's crust, mantle and outer core without
      reflection is called PKP. The outer core is a fluid causing a strong refraction at
      the CMB into the outer core. The strong refraction of the seismic rays into the
      core causes a “core shadow” that commences at epicentral distances of around 100° and
      stretches to around 140°. Only Pdiff can be observed in this distance range. PKP is
      the first arrival at distances larger than around 143°. At a distance of 144° P waves
      with several paths through the Earth’s core arrive at the same time (caustic) and
      form a strong arrival.

   PP phase
      PP is a reflected P wave at the Earth's surface traversing the Earth's crust and mantle.

   pP phase
      A P wave that has a takeoff angle of greater than 90° at the source and therefore
      is first reflected at the surface near the epicenter. The pP is a depth phase.
      For shallow events and at teleseismic distances pP has nearly the same path as the P wave except
      for the path from hypocenter of the earthquake to the reflection point at the surface.

   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.

   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°.

   Sg phase
      Sg is the direct :term:`S wave` arriving first in local distances less than 100 km. For larger
      distances Sn arrives first (see :term:`Sn phase` for details).

   Sn phase
      Sn is the S head wave along the Moho arriving first at local distances larger than
      100 km (depending on the crustal thickness). Sn has usually smaller amplitudes than Sg.

   sP phase
      A P wave starting as an :term:`S phase` at the source and arriving as P.
      The S phase has a takeoff angle greater than 90° at the source and therefore
      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
      wave except for the path from hypocenter of the earthquake to the
      reflection point at the surface.

   pick
      #. Automatic or manual determined phase onset
      #. QuakeML object

   polarity
      In seismology the direction of first motion on a seismogram, either up (positive, compression)
      or down (negative, dilatation or relaxation).

   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
      ground motion is composed of multiple arrivals of seismic rays and related energy
      bundles (Gauss beams) that leave the source and are reflected or refracted at velocity
      boundaries according to Snell's Law. The amplitudes of reflected and refracted waves
      at each boundary are recalculated according to the Law of Conservation of Energy.

   recurrence interval
      The average time span between large earthquakes at a particular site. Also
      termed 'return period'.

   reflection
      The energy or wave from a seismic source that has been returned (reflected) from an
      interface between materials of different elastic properties within the Earth, just
      as a mirror reflects light.

   refraction
      The deflection, or bending, of the ray path of a seismic wave caused by its passage
      from one material to another having different elastic properties.

      Bending of a tsunami wave front owing to variations in the water depth along a coastline.

   relaxation theory
      A concept in which radiated seismic energy is released from stored strain energy
      during the slip along a fault until the adjacent fault blocks reach a new state of equilibrium.

   residual
      #. The difference between the measured and predicted values of some quantity (e.g., theoretical
         and measured phase arrival time).
      #. Attribute of QuakeML object Arrival, see :term:`arrival`.

   Ring of Fire
      The zone of volcanoes and earthquakes surrounding the Pacific Ocean which is called
      the Circum-Pacific belt; about 90% of the world's earthquakes occur there. The next
      most seismic region (5 - 6 % of earthquakes) is the Alpide belt.

   RMS
      Abbreviation for :term:`root mean square <root mean square (RMS)>`

   root mean square (RMS)
      Also referred to as :term:`RMS`. A statistical measure of the magnitude of a varying quantity defined as

      .. math::

         RMS = \sqrt{\frac{{x_1}^2 + {x_2}^2 + {x_3}^2 + ... + {x_n}^2}{N}}

      for the time series with the N elements x\ :sub:`1` to x\ :sub:`n`.

   rupture front
      The instantaneous boundary between the slipping and locked parts of a fault during
      an earthquake. A rupture propagating in one direction on the fault is referred to
      as unilateral. A rupture may radiate outward in a circular manner or it may radiate
      towards the two ends of the fault from an interior point, behavior referred to as
      bilateral.

   rupture velocity
      The speed at which a rupture front moves across the surface of the fault during
      an earthquake.

   SCML
      :term:`SeisComP` Markup Language. SCML is a flavor of `QuakeML
      <https://quake.ethz.ch/quakeml/>`_  and is used by |scname| and by
      products of :term:`gempa GmbH` for exchange. For details read the
      `UML diagram <https://geofon.gfz-potsdam.de/_uml/>`_.

   SDS
      |scname| Data Structure which is used for archiving waveform data. Below the
      base directory of the archive the SDS has the structure:

      .. code-block:: sh

         archive
           + year
             + network code
               + station code
                 + channel code
                   + one file per day and location, e.g. NET.STA.LOC.CHAN.D.YEAR.DOY

   SED
      Specific Energy Density

   SeedLink
      SeedLink :cite:p:`seedlink` is a
      real-time data acquisition protocol and a client-server software that
      implements this protocol

   SeisComP
      SeisComP is likely the most widely distributed software package for
      seismological data acquisition and real-time data exchange over internet.
      Its data transmission protocol SeedLink became a de facto world standard.
      The first version of SeisComP was developed for the `GEOFON
      <http://geofon.gfz-potsdam.de/geofon/>`_ network and further extended
      within the MEREDIAN project under the lead of `GEOFON
      <http://geofon.gfz-potsdam.de/geofon/>`_/`GFZ
      <http://www.gfz-potsdam.de/>`_ Potsdam and `ORFEUS
      <http://www.orfeus-eu.org/>`_. Originally SeisComP was designed as a high
      standard fully automatic data acquisition and (near-)real-time data
      processing tool including quality control, event detection and location as
      well as dissemination of event alerts. In the context of the `GITEWS
      <http://www.gitews.de/>`_ project (German Indian Ocean Tsunami Early
      Warning System) additional functionality were implemented to fulfill the
      requirements of 24/7 early warning control centers. Major changes in the
      architecture of SeisComP were necessary and many new features result in
      the upgrade of SeisComP to version 3. Important SeisComP releases are
      shown below.  A first prototype of :term:`SeisComP3` developed by the
      GITEWS/GEOFON development group was released in May 2007.

   SeisComP3
      A previous version of :term:`SeisComP`.

   seismic array
      An ordered arrangement of seismometers with central data acquisition specially
      designed to analyze seismic signal based on coherent phases. A seismic array
      differs from a local network of seismic stations mainly by the techniques
      used for data analysis. Often, a seismic array are referred to as :term:`array`.

   seismic gap
      A section of a fault that has produced earthquakes in the past but is now quiet.
      For some seismic gaps, no earthquakes have been observed historically, but it is
      believed (based on some other methods, such as plate-motion information, strain
      measurements or geological observations) that the fault segment is capable of
      producing earthquakes. A long-term seismic gap may give hint to the most probable
      location of a strong earthquake in the future.

   seismic moment (M\ :sub:`0`)
      The seismic moment is defined as

      .. math::

         M_0 = \mu D A

      with μ as rigidity of the rock at the fault, D as averaged displacement on the
      fault and A as fault surface area. For pure shear sources, M\ :sub:`0` equals
      the :term:`total seismic moment (MT)`.
      The seismic moment can be related to the released seismic energy ES that is
      proportional to the stress drop Δσ:

      .. math::

         E_S \approx 0.5 \Delta\sigma D A

      Rearranging both equations yields to:

      .. math::

         E_S \approx \frac{\Delta\sigma}{2\mu} M_0

      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

         \log M_0 = 1.5 Ms + 16.1

   seismic network
      Group of seismic stations that are deployed as single stations or arrays.

   seismic ray
      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).

   seismic source
      A localized area or volume generating coherent, usually transient seismic waveforms,
      such as an earthquake, explosion, vibrator etc.

   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`.

   slab
      Usually, the part of the :term:`lithospheric <lithosphere>`
      plate that is underthrusting in a subduction zone and is
      consumed by the Earth's mantle is called slab.

   slab pull
      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.

   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.

   travel-time curve
      A graph of arrival times, commonly of direct as well as multiply reflected and
      converted :term:`P<P wave>` or :term:`S waves<S wave>`, recorded at different
      points as a function of distance
      from the seismic source. Seismic velocities within the Earth can be computed
      from the slopes of the resulting curves.

   XXL event
      An event based on :term:`XXL picks<XXL pick>`.

   XXL pick
      Picks that have extraordinarily large amplitudes and large :term:`SNR<SNR>` and
      that lie within a relatively small region.

   vespagram
      Vespagrams are diagrams of :term:`beam` traces over time typically formed
      for a particular :term:`azimuth` (or :term:`backazimuth`) and for
      ranges of :term:`slowness` (slowness vespagram). When the slowness
      is kept constant and the backazimuth is varied the term backazimuth
      vespagram is used.

   Wadati-Benioff zone
      A dipping planar (flat) zone of earthquakes that is produced by the interaction
      of a downgoing oceanic crustal plate with a continental plate. These earthquakes
      can be produced by slip along the subduction thrust fault (thrust interface between
      the continental and the oceanic plate) or by slip on faults within the downgoing
      plate as a result of bending and extension as the plate is pulled into the mantle.
      Slip may also initiate between adjacent segments of downgoing plates. Wadati-Benioff
      zones are usually well-developed along the trenches of the Circum-Pacific belt,
      dipping towards the continents.

   wave number
      Number of cycles of a repeating signal per unit length, typically per meter of kilometer.

   P wave
      P (primary) waves are compressional waves involving volumetric variations in the
      media. The sense of particle motion is linear and parallel to the propagation
      direction. P waves are body waves that traverse the interior of a body/Earth and
      can propagate in fluids.

      The general nomenclature for P waves: At local and
      regional distances a special nomenclature is used to describe the travel path of
      the first P and S arrivals. Pg, Pb/P* and Pn phases are separated. Pg is the direct
      P wave arriving first in distances less than around 100 km. Pn is the head wave
      along the Moho arriving first at larger distances than 100 km (depending on the
      crustal thickness). Pn has usually smaller amplitudes than Pg. Pb or P* is the
      rarely observed head wave travelling along the midcrustal velocity discontinuity.
      The general nomenclature of P waves entitles reflections at the topside of boundaries
      with lowercase letters (m – Moho reflection; c - CMB reflection; i - inner core-outer
      core boundary reflection), e.g. PmP is a reflected P wave at the Moho. Reflections
      at the bottom side of boundaries get no additional letter, e.g. PP is a reflected
      P wave at the Earth's surface. Refracted rays get capital letters (K - through
      the outer core; I - through the inner core), e.g. PKIKP is a P wave traversing
      the crust/mantle, the outer core, the inner core, again the outer core and again
      the mantle/crust.

   S wave
      S (secondary) waves are shear waves without any volumetric variation in the media.
      The sense of particle motion is perpendicular to the propagation direction. S waves
      are body waves that traverse the interior of a body but can not propagate in fluids.

      Analog to the P arrivals Sg, Sb/S\ :sup:`*` and Sn arrivals are distinguished in local
      and regional distances. The general nomenclature of S waves is analog to the P waves.
      The reflections at the topside of boundaries have lowercase letters (m - Moho
      reflection; c - CMB reflection), e.g. SmS is a reflected S wave at the Moho.
      Reflections at the bottom side of boundaries get no additional letter, e.g. SS is a
      reflected S wave at the Earth's surface. Refracted rays get capital letters (J - through
      the inner core), e.g. SKJKS is a S wave traversing the crust/mantle, the outer core
      as a :term:`P wave`, the inner core as a :term:`S wave`, again the outer core as a P wave and again
      the mantle/crust as S wave. S waves can not travel through the outer core because
      the outer core consists of a fluid.

   surface wave
      Surface waves are seismic waves observed only at the free surface of the media.
      Two types of surface waves are distinguished: :term:`Love waves<Love wave>` (L)
      and :term:`Rayleigh waves<Rayleigh wave>` (R).
      Both result from the interaction of P and S waves near the free surface.

   waveform (data)
      The complete analog or sufficiently dense sampled digital representation of a
      continuous wave group (e.g., of a seismic phase) or of a whole wave train
      (seismogram). Accordingly, waveform data allow to reconstruct and analyze the
      whole seismic phase or earthquake record both in the time and frequency domain
      whereas parameter data describe the signal only by a very limited number of more
      or less representative measurements such as onset time, maximum signal amplitude
      and related period.

   waveformID
      Attribute of the QuakeML objects Pick, !StationAmplitude and !StationMagnitude
      describing the source of the underlying waveform source. The WaveformID contains
      information about the !NetworkCode, !StationCode, !LocationCode and !ChannelCode

   wave front
      The surface formed by all elements of a propagating wave, which swing in phase;
      the wave front is perpendicular to the seismic rays, which are oriented in
      direction of wave propagation.

   wavelength
      The distance between successive points of equal amplitude and phase on a
      wave (for example, crest to crest or trough to trough).

   weight
      Attribute of the QuakeML objects Arrival and !MagnitudeReferences defining the
      effect of the referenced object (e.g. Pick).

   Wood-Anderson seismometer
      Torsion seismometer recording horizontal displacement
      :term:`amplitudes <amplitude>` described in :cite:t:`richter-1935` and
      :cite:t:`uhrhammer-1990`. Simulation of the Wood-Anderson seismometer is
      used for measuring amplitudes for selected :term:`magnitudes <magnitude>`.
      SeisComP3 and SeisComP in versions 4 and 5 have considered Wood-Anderson
      instrument parameters originally published by :cite:t:`richter-1935` with
      gain = 2800, T0 = 0.8 s, h = 0.8. However, updated parameters where
      published by :cite:t:`uhrhammer-1990` with gain = 2080, T0 = 0.8 s,
      h = 0.7. These values were part of the IASPEI Magnitude Working Group
      recommendations of 2011 September 9 and therefore apply by default in later
      versions of SeisComP. With the original set of values
      :cite:p:`richter-1935`, magnitudes are systematically overestimated by 0.13.
      Wood-Anderson seismometers can be simulated by filtering waveforms with
      :func:`WA`.

   WWSSN_SP
      Short period seismograph with a dominant period of 1 s of the World-Wide
      Standard Seismograph Network (WWSSN). WWSSN_SP instruments can be simulated
      by filtering waveforms with :func:`WWSSN_SP`.

   WWSSN_LP
      Long period seismograph with a dominant period of 20 s of the World-Wide
      Standard Seismograph Network (WWSSN). WWSSN_LP instruments can be simulated
      by filtering waveforms with :func:`WWSSN_LP`.

   XML
      Extensible Markup Language a version of which is :term:`SCML`.


Distance terms
--------------

.. glossary::

   distance, epicentral
      The epicentral distance is defined as the shortest distance from a seismic
      station or any other site to the epicentre of the seismic event.

   distance, hypocentral
      The hypocentral distance is defined as the shortest distance from a
      seismic station or any other site to the hypocentre of the seismic event.
