Determination of spectral properties of earthquakes from their magnitudes

Abstract

Following the recommendation of the “IASPEI Commission on Magnitudes” from 1967, P-wave magnitudes of distant earthquakes are being computed with the aid of the calibration functions of Gutenberg and Richter (1956). With the development of the instrumental seismology, especially in view of the availability of broad-band recordings, the question arises whether the functions are still adequate. In this investigation new calibration functions for P- and S-waves are presented, which are not only dependent on epicentral distance and focal depth, but also on the period of the spectral component of the wave. The determination of calibration functions is based on the currently most plausible global models for the velocity and anelasticity distribution. Taking into account the effective bandwidth of the instruments employed, eventually leads to the so-called spectral magnitudes. From the spectral magnitudes m( T) , the energy density spectrum E( T) of the respective wave can readily be computed. The corresponding formula is E( T) = 10 2m(T)− 1.4, with E( T) in joules per hertz.