Moment tensor inversion for near earthquakes using long-period digital seismograms.

Abstract

The possibility of rapid determination of source parameters (seismic moment and fault parameters) for near earthquakes is examined by means of the moment tensor inversion method. Numerical experiments of linear moment tensor inversion are made for a hypothetical source-station geometry appropriate for the Japanese region and suggest that it may be possible to determine the source parameters for the near earthquakes within about 10 min after the earthquake occurrence, provided that high-quality long-period seismic waveform data can be used. Source parameters of eight earthquakes (MW > 6.0) which occurred near the Japanese region during the period from November 1986 to April 1987 are determined by applying the inversion method to three-component long-period digital data recorded at a single station in Japan. The obtained source parameters are in good agreement with the solutions derived from global networks. The centroid-moment tensor (CMT) inversion method, solution of which is a result of simultaneous inversion of waveform data for the hypocentral parameters (epicentral coordinates, depth, origin time, and moment tensor) of the best point source, is applied to both synthesized and observed data. The inversion of synthesized data suggests that the CMT inversion to determine the hypocentral and source parameters simultaneously for near earthquakes may be possible in the Japanese region. We applied this method to the eight events, but we could obtain the CMT solution for only one event. The short propagation time and inadequate station coverage in the case of the single-station observation of the near earthquakes might have caused the non-uniqueness and instability in the determination of the CMT solutions. The numerical experiments suggest that this problem may be significantly remedied by the improvement of the station coverage.