Foreshocks and aftershocks accompanying a perceptible earthquake in central japan

Abstract

A small perceptible earthquake and its 25 foreshocks and 173 aftershocks were recorded by a special tripartite observation of high sensitivity set up in the Matsushiro Seismological Observatory. A substantial difference was found between the foreshocks and aftershocks in the relation of frequency of occurrence and magnitude, i. e. the coefficient “b” in Gutenberg-Richter's formula is only 0.35 in the former as against 0.76 in the latter. This is discussed with the general seismicity of the region. Some relations between main shocks and their aftershocks have been found to hold good also in the present example of a miniature size; namely, the main shock occurred on the margin of the foreshock and aftershock region, and the size of the region is as small as expected from the magnitude of the main shock. © 1964, Japan Meteorological Agency. All rights reserved.