Local Magnitude (Ml) 1
Local Magnitude (Ml) 1 : A magnitude scale introduced by Richter (1935) for earthquakes in southern California. ML was originally defined as the logarithm of the maximum amplitude of seismic waves on a seismogram written by the Wood-Anderson seismograph (Anderson and Wood, 1925) at a distance of 100 km from the epicenter. In practice, measurements are reduced to the standard distance of 100 km by a calibrating function established empirically. Because Wood-Anderson seismographs have been out of use since the 1970s, ML is now computed with a simulated Wood-Anderson records and a slightly modified standard formula. The original ML scale calibration function is only valid for the seismic wave attenuation conditions in California. Therefore, when adopting the ML scale to other regions, many authors use the original Richter definition together with a modified calibration function. See the biography of Charles Francis Richter in Howell (2003), Chapter 3, DS 3.1 and IS 3.3 in this Manual, the IASPEI (2011) magnitude standards, and Bormann (2011)
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