MLv

Local (Richter) magnitude measured on the vertical component

Description

MLv is the local (Richter) magnitude (Richter [58]) computed from amplitudes measured on the vertical component.

General (default) conditions apply:

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

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

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

  • Depth range: no limitation.

Amplitudes

The MLv amplitude calculation is very similar to the original ML, except that the amplitude is measured on the vertical component. The methods for measuring amplitudes are configurable in the global bindings.

Station Magnitudes

The individual station MLv is calculated up to the epicentral distance magnitudes.MLv.maxDistanceKm using the following formula:

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

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

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

The logA0 configuration string consists of an arbitrary number of distance-value pairs separated by semicolons. The distance is in km and the 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

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

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

Network magnitude

By default, the trimmed mean is calculated from the station magnitudes to form the network magnitude. Outliers beyond the outer 12.5% percentiles are removed before forming the mean.

Configuration

Several distance-value pairs can be configured for different ranges of epicentral distance. The calibration function and maximum distance can be configured globally, per network or per station using the configuration variables. Instead configuring lots of global bindings profiles or station bindings one line per parameter can be added to the global module configuration (global.cfg), e.g.

global:

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

or per network:

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

or per station:

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

Set the configuration and calibration parameters in the global bindings. By default MLv is computed by scautopick and is visible in GUIs.