Earthquakes: Magnitude, Energy, and Intensity
Development of the Concepts
The focus of an earthquake radiates mechanical energy in the form of seismic waves. The radiation of seismic energy during the event continues from a fraction of a second to several tens of seconds. The duration of seismic wave radiation is identical with that of the instantaneous faulting.
The time between two radiation events from a given focus is substantially larger than the radiation duration of a given event. Thus, earthquakes are transient radiation phenomena, and the methods for the determination of the strength of sources radiating transient signals are correspondingly applicable. On this basis the earthquake magnitude scale was introduced. A steady development of the magnitude concept is necessitated by ongoing improvements in seismological instrumentation and in the theories of the focal process and of seismic wave propagation.
A comprehensive review of the magnitude problem was