著者

Mogi Kiyoo

出版者

東京大学地震研究所

雑誌

東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)

巻号頁・発行日

vol.41, no.3, pp.615-658, 1963-09-30

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In the preceding papers40', the patterns of the successive occurrence of elastic shocks accompanying fractures under a simple stress state have been experimentally investigated and they have been classified into three types. The type of shock sequence is decidedly influenced by the mechanical structure of model materials. In this paper, this experimental conclusion has been applied to earthquakes in and near Japan (1926-1961). The main results are summarized as follows. (1) The patterns of earthquake sequences are also classified into the three types which were obtained in the patterns of shock sequences, but the transition from one to another is continuous. (2) About 60 earthquakes preceded by foreshocks (the second type)'have been found. They distribute in groups at certain regions. In such regions where the normal sequence of foreshocks is expected, the seismic- observations may give a clue for prediction of major earthquakes. (3) The regions where a certain type of earthquake sequence frequently appears distribute following a general tendency. The various patterns of earthquake sequences are related to the various degrees of heterogeneity in structure. Thus, the spatial distribution of the regions fractured in various degrees are deduced from the data of the patterns of earthquake sequences. (4) The probability P that an earthquake is followed by aftershocks increases with the magnitude and decreases with the focal depth. Furthermore, the P value varies remarkably in various regions. The spatial distribution of the regions having a high P value of aftershock occurrence is nearly identical to that of the second type and the third type. These regions are also the regions which are fractured to some degree. (5) The spatial distribution of fractured regions deduced from the types of the pattern of earthquake sequences has close relations to various geotectonic structures of the Japanese islands, and to other geophysical data.