chapter  3
44 Pages


Earthquake Magnitude The size, or magnitude, of an earthquake is expressed as a decimal number (e.g., 6.8). In 1931, the Japanese seismologist Kiyoo Wadati devised the fi rst quantitative magnitude scale; in 1935 it was further developed by Charles F. Richter at the California Institute of Technology. The scale became known in the popular press as the Richter scale . It quantifi ed the magnitude of local (California) earthquakes as the logarithm to the base 10 of the maximum signal wave amplitude recorded on a then-standard seismogram at a distance of 100 km from the epicentre.