wiki:HowTo/LocalMagnitudeFormula

Local magnitude formula

Seismic Handler in version 2013a supports a new analytical formula for local magnitude estimation (Richter magnitude). Whereas the classic mode (default) uses tabulated values for distance correction, the IASPEI recommended formula reads as

Local magnitude fomula

  • D is distance in kilometers and
  • A is the measured amplitude in nm using a Wood-Anderson simulation trace.
  • parameters 1.11, 0.0089 and 2.09 are configurable from version 2013b? onwards.

Differences between methods

The resulting magnitudes may show quite large differences. The next figure displays the offset between the formulas:

Systematic deviation between classic and new formula

One can easily see, that the systematic offset varies between -0.2 and 0.4 magnitude units.

Using the new formula

Because of the large differences to the classic approach we decided to set the new formula not as default for new installations. In order to activate the new method simply change the value of local_magnitude_formula to iaspei in shm-config.txt. In SHM you can access this file using the Specials -> Configure menu. If you just want to update your existing configuration file, add the line local_magnitude_formula iaspei.

Using version 2013b? also the parameters of this formula can be changed.

Attachments

  • ml.png Download (1.2 KB) - added by MarcusWalther 6 years ago. Local magnitude fomula
  • deviation.png Download (23.8 KB) - added by MarcusWalther 6 years ago. Systematic deviation between classic and new formula