Synthesis of Three-Component Seismogram Envelopes of a Small Earthquake

Abstract

The initial direction of motion of the P-wave, the amplitudes of the direct P- and S-waves, and the high-frequency character of the P- and S-coda envelopes on all three components of motion from a local microearthquake are influenced by the angle between the fault plane and the receiver and the scattering characteristics of the lithosphere. To better understand the effects of scattering on recorded regional seismograms, we desire a method to synthesize three-component seismogram envelopes for realistic earthquake sources in an inhomogeneous medium. The simplest way to synthesize seismograms is to sum up all waves scattered by distributed heterogeneities in the time domain. It is easier to synthesize the MS envelope by adding the power of scattered waves. Assuming the complete incoherence of scattered waves, Malin (1980) synthesized the MS acoustic-wave envelope by summing up scattered wave power. Extending the method of summing up single scattered energy, we will present a way to synthesize three-component seismogram envelopes resulting from realistic earthquake sources in an infinite random medium, where S-wave polarization is carefully treated (Sato 1984a).