Moment tensor inversion of complex earthquakes

Abstract

Summary. Moment tensor inversion methods can be applied with success in the determination of source properties of simple earthquakes. However, these methods utilize the assumption of a point source, which is inadequate for modelling many complicated, shallow earthquakes. For complex earthquakes, an inversion using finite faulting models is desirable but the number of parameters involved requires that a good starting model be found or that independent constraints be placed on some of the parameters. A method is presented for low‐pass filtering both the data and Green's functions, passing only signals with wavelengths greater than the dimension of the entire fault. The filter tends to smooth complications in the waveforms and allows application of the point source moment tensor inversion. This method is applied to body waves from the 1978 Thessaloniki, Greece, earthquake, the 1971 San Fernando earthquake and to a multiple‐point source synthetic model of the San Fernando event. For the Thessaloniki event, although a multiple‐source mechanism has been suggested, inversion results before and after filtering were essentially identical, indicating that a point source mechanism is sufficient in modelling the long‐period, teleseismic body waves. In the case of the San Fernando earthquake, the point source Green's functions were incapable of simultaneously modelling the P‐ and SH‐waves. Inversion of P‐waves alone resulted in extreme parameter resolution problems, but allowed constraint in one axis of the moment tensor and suggested an overall source time function. Inversion of a synthetic San Fernando data set yielded similar results, but allowed an investigation of the shortcomings of the method under controlled circumstances. Although the results may require substantial interpretation, the method presented represents a simple first step in the analysis of complex earthquakes. Copyright © 1982, Wiley Blackwell. All rights reserved

Publication Title

Geophysical Journal of the Royal Astronomical Society

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