176 lines
6.9 KiB
ReStructuredText
176 lines
6.9 KiB
ReStructuredText
.. _concepts_magnitudes:
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Magnitudes
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##########
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Magnitudes are computed based on amplitudes measured from waveforms. Different
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types of amplitudes and magnitudes are available which are listed in
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:ref:`scamp` and :ref:`scmag`.
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Amplitudes
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==========
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Amplitudes can be measured automatically from waveforms
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* During phase picking by :ref:`scautopick` with generally fixed time windows
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due to the absence of knowledge about source parameters or by,
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* :ref:`scamp` as soon as :term:`origins <origin>` are available. Depending
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on the magnitude type, fixed or distance-dependent time windows apply.
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and interactively using :ref:`scolv`.
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Instrument simulation
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---------------------
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Amplitude measurements for some magnitude types require or allow the simulation
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of instruments such as :py:func:`Wood-Anderson torsion seismometers <WA>`
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(:cite:t:`richter-1935,uhrhammer-1990`), :py:func:`WWSSN_SP` or :py:func:`WWSSN_LP`.
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The calibration parameters describing the Wood-Anderson seismometer are
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configurable in global bindings or global module configuration:
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:confval:`amplitudes.WoodAnderson.gain`, :confval:`amplitudes.WoodAnderson.T0`,
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:confval:`amplitudes.WoodAnderson.h`. Specifically, the difference in magnitude
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due to configuration using original values listed in
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:cite:t:`richter-1935` and updated ones given in :cite:t:`uhrhammer-1990`
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result in a constant offset of 0.13 in those magnitudes which apply
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Wood-Anderson simulation, e.g. :term:`ML <magnitude, local (ML)>`,
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:term:`MLv <magnitude, local vertical (MLv)>`, :term:`MLc <magnitude, local custom (MLc)>`.
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Station Magnitudes
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==================
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Station magnitudes are computed automatically by :ref:`scmag` or interactively
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by :ref:`scolv` from measured amplitudes based on distance-dependent
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calibration curves which depend on magnitude type. When computing a set of
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magnitudes in :ref:`scolv` which is different from the set configured in
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:ref:`scmag`, then scmag may later add the missing magnitudes automatically.
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Magnitude types for which the evaluation status is set to "rejected", e.g., in
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scolv, will not be recomputed by scmag.
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.. _concepts-magnitudes-correction:
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Station corrections
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-------------------
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Linear station corrections applied to station magnitudes can be configured by
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global :ref:`binding parameters <global_bindings_config>`:
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#. Add a magnitude type profile where the name of the profile is the name of the
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magnitude itself,
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#. Configure the correction parameters.
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When using binding profiles, all referencing stations will be affected equally
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which is typically not intended. In contrast, applying station bindings requires
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to set up many bindings which may not be intended either.
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Therefore, you may add lines to the global module configuration in
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:file:`global.cfg` where one line corresponds to one station with one magnitude
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and the corresponding correction parameter. The groups and the name of the
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parameters are identical to the global bindings parameters. All lines start with
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"*module.trunk*". Example for an offset correction of
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:term:`MLv <magnitude, local vertical (MLv)>` measured station GE.UGM:
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.. code-block:: properties
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module.trunk.GE.UGM.magnitudes.MLv.offset = 0.1
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.. note::
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The configuration of parameters starting with *module.trunk.* is not
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supported by :ref:`scconfig`. All corresponding configurations must be done
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by direclty editing the configuration file, e.g.,
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:file:`seiscomp/etc/global.cfg`.
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Network Magnitudes
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==================
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Network magnitudes are computed automatically by :ref:`scmag` or interactively
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by :ref:`scolv` from station magnitudes based on averaging station magnitudes.
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The averaging methods applied by :ref:`scmag` are configurable by
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:confval:`magnitudes.average`. Available are (:cite:t:`rosenberger-1983`):
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* *mean*: the mean value from all station magnitudes.
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* *median*: the mean value from all station magnitudes.
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* *trimmedMean(X)*: gnores outlier station magnitudes by first removing the
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largest and the smallest *X* % of the observed values (percentiles). The mean is
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formed from the remaining station magnitudes.
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* *trimmedMedian(X)*: forms the median from all station magnitudes but returns
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the uncertainty by ignoring the largest and the smallest *X* % station
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magnitudes.
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* *medianTrimmedMean(X)*: returns the mean magnitude from all station magnitudes
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differing less than *X* magnitudes from the median.
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Aliases
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=======
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New magnitude types (aliases) can be created based on existing magnitude and
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amplitude types but configured specifically.
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The setup procedure is outlined in the
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:ref:`tutorial on magnitude aliases <tutorials_magnitude-aliases>`.
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.. _concepts-magnitudes-regionalization:
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Regionalization
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===============
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The computation of station magnitudes can be regionalized. This means that for
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a specific region specific conditions apply when computing magnitudes. The
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conditions include any parameter available for configuring a magnitude
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including global binding parameters such as magnitude calibration, distance
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and depth ranges, etc. As an example you may wish to apply different
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attenuation curves for computing MLv magnitudes to earthquakes in Eastern and
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in Western Canada.
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Regionalization is achieved by adding magnitude-type profiles in the magnitudes
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section of global module configuration parameters. Regionalization assumes
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defaults from global bindings but overrides the values when configured. The
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setup procedure including
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:ref:`station corrections <concepts-magnitudes-correction>` is outlined in the
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:ref:`tutorial on regionalization <tutorials_magnitude-region-aliases>`.
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Moment Magnitudes
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=================
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Moment magnitudes can be derived from all other network magnitudes by mapping of
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the original network magnitude, e.g., *Mx*, to a new moment magnitude *Mw(Mx)*.
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The mapping function can be configured for all original magnitude types except
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:term:`mB <magnitude, derived mB (Mw(mB))>` and
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:term:`Mwp <magnitude, derived Mwp (Mw(Mwp))>` where the mapping is hardcoded.
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Read the :ref:`tutorial on moment magnitudes <tutorials_mags_moment>` for the
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configuration.
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.. _concepts-magnitudes-summary:
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Summary Magnitude
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=================
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In order to account for different phenomena related to magnitude computation
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including magnitude saturation and application of different magnitude types at
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specific distance and depth ranges of the sources a summary magnitude can be
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computed from network magnitudes by :ref:`scmag`. The summary magnitude is
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usually referred to as *M*. The name is configurable.
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.. note::
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Station, network and summary magnitudes are contained uniquely in one
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:term:`origin`.
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Preferred Magnitude
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===================
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From the list of computed network magnitudes and the summary magnitude,
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:ref:`scevent` can automatically determine the preferred magnitude of the
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:term:`event`. This may also be done interactively by operators in the
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:ref:`Event tab of scolv <scolv-sec-event-tab>` or by
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:ref:`custom commit buttons in scolv <sec-scolv-custom-commit>`.
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