Magnitude, seismic moment and apparent stress for major deep earthquakes

Abstract

On the basis of an extensive data-set of major deep and intermediate-depth earthquakes, the relation between body-wave magnitude mB and seismic moment M0 is discussed in terms of apparent stress. mB is determined from amplitudes and periods of P, PP and S waves recorded by broad-band instruments, and is therefore suitable for measuring the overall size of major earthquakes. The relation between mB and log M0 is approximately linear for the data set of mB greater than 6. This indicates that the apparent stress is, on the average, nearly constant. A gross average of 60 bar is obtained for the earthquakes over a large depth range. For a simple fault model, we have ES=(7.10∼S)M0, where EB is the radiated seismic energy. The constant apparent stress implies a decrease of seismic efficiency with an increase of depth. A very similar relation between mB and log Mo is applicable to large shallow earthquakes. © 1982, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan. All rights reserved.