Earthquake duration magnitude (Md) for earthquakes recorded on short-period vertical seismographs. Numerous studies determined the relation between coda duration and magnitude for different regions of the World. According to a recent study by Mandal et al. (2004), previous studies showed that duration magnitude estimation is quite stable for local earthquakes ranging from magnitude Md 0.0 to 5.0. In two most recent investigations using statistically stable samples for Italian earthquakes [approximately 100,000 events over the period 1981-2002 in the Richter local [ML] magnitude range of 3.5-5.8] and for Indian earthquakes exemplified by an aftershock sequence of 121 events with (surface wave magnitude) > 4.0
Richter magnitude scale corrections, in that for distances less than 200 kilometers the attenuation is strongly affected by the structure and properties of the regional geology. When Richter presented the resulting scale in 1935 he called it (at the suggestion of Harry Wood) simply a "magnitude" scale. "Richter magnitude" appears to have originated when Perry Byerly told the press that the scale was Richter's, and "should be referred to as such." In 1956 Gutenberg and Richter, while still referring to "magnitude scale", labelled it "local magnitude", with the symbol , to distinguish it from two other scales they had developed, the surface wave