地震波形の相似性からみた前震と群発地震の違いについて(序報)

概要

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The earthquake swarms occurred at seven areas distributed in the Kanto district and foreshocks preceding the Izu-Oshima-kinkai earthquake (M=7.0) of 1978 are studied through the analysis of waveform. The earthquakes in a given swarm activity usually share a similar waveform, and the arrival times for certain isolated waves measured from the P-wave onset of their events are the same within the deviation of 0.1 sec. Especially when earth- quakes of similar size are compared, their waveforms frequently coincide from P-wave onset till coda waves. Similar behavior, but with different waveforms are seen for earthquake swarms occurring in other areas. On the other hand, the waveform of foreshocks differs significantly from event to event even if the events occurred within a short time interval (e.g., 1 hour). If such features are always observed, the present results will be useful for the discrimination of swarm activity from other earthquake activity such as the foreshocks of a major earthquake.
1979-12-25