Magnitudes

Magnitudes are computed based on amplitudes measured from waveforms. Different types of amplitudes and magnitudes are available which are listed in scamp and scmag.

Amplitudes

Amplitudes can be measured automatically from waveforms

  • During phase picking by scautopick with generally fixed time windows due to the absence of knowledge about source parameters or by,

  • scamp as soon as origins are available. Depending on the magnitude type, fixed or distance-dependent time windows apply.

and interactively using scolv.

Instrument simulation

Amplitude measurements for some magnitude types require or allow the simulation of instruments such as Wood-Anderson torsion seismometers (Richter [57], Uhrhammer and Collins [63]), WWSSN_SP() or WWSSN_LP(). The calibration parameters describing the Wood-Anderson seismometer are configurable in global bindings or global module configuration: amplitudes.WoodAnderson.gain, amplitudes.WoodAnderson.T0, amplitudes.WoodAnderson.h. Specifically, the difference in magnitude due to configuration using original values listed in Richter [57] and updated ones given in Uhrhammer and Collins [63] result in a constant offset of 0.13 in those magnitudes which apply Wood-Anderson simulation, e.g. ML, MLv, MLc.

Station Magnitudes

Station magnitudes are computed automatically by scmag or interactively by scolv from measured amplitudes based on distance-dependent calibration curves which depend on magnitude type. When computing a set of magnitudes in scolv which is different from the set configured in scmag, then scmag may later add the missing magnitudes automatically. Magnitude types for which the evaluation status is set to “rejected”, e.g., in scolv, will not be recomputed by scmag.

Station corrections

Linear station corrections applied to station magnitudes can be configured by global binding parameters:

  1. Add a magnitude type profile where the name of the profile is the name of the magnitude itself,

  2. Configure the correction parameters.

When using binding profiles, all referencing stations will be affected equally which is typically not intended. In contrast, applying station bindings requires to set up many bindings which may not be intended either.

Therefore, you may add lines to the global module configuration in global.cfg where one line corresponds to one station with one magnitude and the corresponding correction parameter. The groups and the name of the parameters are identical to the global bindings parameters. All lines start with “module.trunk”. Example for an offset correction of MLv measured station GE.UGM:

module.trunk.GE.UGM.magnitudes.MLv.offset = 0.1

Note

The configuration of parameters starting with module.trunk. is not supported by scconfig. All corresponding configurations must be done by direclty editing the configuration file, e.g., seiscomp/etc/global.cfg.

Network Magnitudes

Network magnitudes are computed automatically by scmag or interactively by scolv from station magnitudes based on averaging station magnitudes. The averaging methods applied by scmag are configurable by magnitudes.average.

Aliases

New magnitude types (aliases) can be created based on existing magnitude and amplitude types but configured specifically. The setup procedure is outlined in the tutorial on magnitude aliases.

Regionalization

The computation of station magnitudes can be regionalized. This means that for a specific region specific conditions apply when computing magnitudes. The conditions include any parameter available for configuring a magnitude including global binding parameters such as magnitude calibration, distance and depth ranges, etc. As an example you may wish to apply different attenuation curves for computing MLv magnitudes to earthquakes in Eastern and in Western Canada.

Regionalization is achieved by adding magnitude-type profiles in the magnitudes section of global module configuration parameters. Regionalization assumes defaults from global bindings but overrides the values when configured. The setup procedure including station corrections is outlined in the tutorial on regionalization.

Moment Magnitudes

Moment magnitudes can be derived from all other network magnitudes by mapping of the original network magnitude, e.g., Mx, to a new moment magnitude Mw(Mx).

The mapping function can be configured for all original magnitude types except mB and Mwp where the mapping is hardcoded. Read the tutorial on moment magnitudes for the configuration.

Summary Magnitude

In order to account for different phenomena related to magnitude computation including magnitude saturation and application of different magnitude types at specific distance and depth ranges of the sources a summary magnitude can be computed from network magnitudes by scmag. The summary magnitude is usually referred to as M. The name is configurable.

Note

Station, network and summary magnitudes are contained uniquely in one origin.

Preferred Magnitude

From the list of computed network magnitudes and the summary magnitude, scevent can automatically determine the preferred magnitude of the event. This may also be done interactively by operators in the Event tab of scolv or by custom commit buttons in scolv.