ML

Standard local (Richter) magnitude

Description

ML is the standard local (Richter) magnitude originally designed for Southern California by Richter [58].

General (default) conditions apply:

  • Amplitude unit in SeisComP: millimeter (mm) by simulation of a Wood-Anderson seismometer.

  • Time window, configurable: 150 s by scautopick or distance dependent, configurable.

  • Distance type: epicentral distance.

  • Distance range: 0 - 8 deg, maximum is configurable: magnitudes.ML.maxDistanceKm, measurements beyond 8 deg will be strictly ignored.

  • Depth range: 0 - 80 km, configurable for amplitude measurements.

Amplitudes

The ML amplitude calculation is similar to the original ML. Waveforms from both horizontal components are time-windowed and restituted to the Wood-Anderson seismograph. Within the time window the amplitudes are measured on both horizontal components and combined. The methods for measuring and combining amplitudes are configurable in the global bindings.

Station Magnitudes

The individual station ML is calculated using the following formula:

ML = \log10(A) - \log10(A0)

A is the measured ML Wood-Anderson amplitude in millimeters. The second term is the empirical calibration function, which in turn is a function of the epicentral distance (Richter [58]). This calibration function and distance range can be configured globally or per station using global bindings or the global module configuration variable module.trunk.global.magnitudes.ML.logA0 in global.cfg, e.g.

module.trunk.global.magnitudes.ML.logA0 = "0:-1.3,60:-2.8,100:-3.0,400:-4.5,1000:-5.85"
module.trunk.global.magnitudes.ML.maxDistanceKm = "-1"

The logA0 configuration string consists of an arbitrary number of distance-value pairs separated by comma. Within the pairs, the values are separated by colon. The distance is epicentral distance in km and the second value corresponds to the log10(A0) term above.

Within each interval the values are computed by linear interpolation. E.g. for the above default specification, at a distance of 80 km the log10(A0) value would be

\log10(A0) &= ((-3.0)-(-2.8))*(80-60)/(100-60)-2.8 \\ &= -2.9

In other words, at 80 km distance the magnitude would be

ML &= \log10(A) - (-2.9) \\ &= \log10(A) + 2.9

which is according to the original Richter formula [58] if the amplitude is measured in millimeters.

Several distance-value pairs can be configured for different ranges of epicenter distance.

Network magnitude

By default, the mean is calculated from the station magnitudes to form the network magnitude.

Configuration

Set the configuration and calibration parameters in the global bindings similar to MLv. Instead configuring lots of global bindings profiles or station bindings one line per parameter can be added to the global module configuration (global.cfg).

Add ML to the list of computed amplitudes and magnitudes in the configuration of scamp and scmag and in scesv or scolv for visibility.