Richter magnitude scale Richter magnitude scale The so-called Richter magnitude scale – more accurately, "Richter's magnitude scale", or just "Richter magnitude" – for measuring the strength ("size") of earthquakes refers to the original "magnitude scale" developed by Charles F. Richter and presented in his landmark 1935 paper, and later revised and renamed the Local magnitude scale, denoted as "ML" or "M". Because of various shortcomings of the ML scale most seismological authorities now use other scales, such as the moment magnitude scale (), to report earthquake magnitudes, but much of the news media still refers to these as "Richter" magnitudes. All magnitude scales
Seismic magnitude scales times. As originally defined by m was based on the maximum amplitude of waves in the first 10 seconds or more. However, the length of the period influences the magnitude obtained. Early USGS/NEIC practice was to measure on the first second (just the first few P-waves), but since 1978 they measure the first twenty seconds. The modern practice is to measure short-period scale at less than three seconds, while the broadband scale is measured at periods of up to 30 seconds. The regional mb scale – also denoted mb_Lg, mbLg, MLg (USGS), Mn, and m – was developed by for