Comparison of the aftershock distribution and the fault plane size of the M 4.9 Kameoka earthquake on May 28, 1987, Japan

Abstract

It has been pointed out in several investigations that an aftershock gap exists in the neighborhood of the main shock, where the main shock slip is large for large earthquakes. Since the source process of small earthquakes is thought to be less complex than that of large earthquakes, it is expected that by comparing the size of the fault plane and the pattern of aftershock distribution for small earthquakes the physical meaning for large earthquakes may be clarified. The 28 May 1987 Kameoka earthquake with M 4.9 occurred in the midst of a telemetered seismic network and the data, therefore, were recorded with high accuracy. The aftershocks were relocated by means of the master event technique with the aftershock gap found in the neighborhood of the hypocenter of the main shock. P wave forms radiated by the Kameoka earthquake were observed with low-gain velocity seismographs having a natural period of 10 s without saturation. The fault plane size was estimated by comparing observed seismograms having small hypocentral distances with synthetic seismograms obtained by forward modeling. It was shown that the gap of aftershocks was comparable to the fault plane size of the small earthquake such as the M 4.9 Kameoka earthquake.