著者

関谷 溥

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.79, no.3, pp.175-180, 1970-06-25 (Released:2009-11-12)

参考文献数

7

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September 1, 1923, southern Kanto was devastated by a severe earthquake. The main shock of the events, which occurred at 11 h 58 m (JST), was felt all over Japan. The highest seismic intensity is 7 in JMA scale at the southern part of Kanagawa, Tokyo and Chiba prefectures. The epicenter is located on the Sagami-nada. Parameters of the main shock given by the Japan Meteorological Agency are as follows ;origin time : 11 h 58 m, September 1, 1923.epicenter : 35° 20' N, 139° 20' Emagnitude : 7.9The earthquake was accompanied by many fore- and after-shocks. The foreshocks occurred in Kashima-nada. It seems that the foreshock activities began in May 1923 and became vigorous in June 1923 before the occurrence of the main shock.The aftershocks occurred in Kanagawa, Yamanashi, Saitama, Chiba, Ibaraki prefectures and near seas, and the general trend in decrease of daily number of the aftershocks can be explained by Omori's generalized formula.

著者

関谷 溥

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.29, no.3, pp.299-311, 1976-09-15 (Released:2010-03-11)

参考文献数

7

被引用文献数

4 10

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The Izuhanto-oki earthquake of May 9, 1974 (M6.9) was preceded by an anomalous seismicity as shown Fig. 1. The duration from the anomalous Seismicity to the mainshock was about 10 years and 4 months. Similar phenomena were also found for 10 events which occurred at shallow depths in Japan.Considering that these data show a linear relation between the magnitude of earthquakes M and duration log T (day), the author calculated the coefficient of logT=bM+a by using the method of least squares as follows: logT=bM+a=0.77M-1.65The relation between the above formula and that of TSUBOKAWA (1969), RIKITAKE (1975) and SCHOLZ et al. (1973), which indicate with a certain accuracy the magnitude and time of an expected earthquake was given by Fig. 7.The author believes that the anomalous seismicity preceding earthquakes is one of the potential parameters which could be employed for earthquake prediction. On the other hand, in some certain fracture zones were found a premonitory change before some events. These phenomena generally are called foreshocks. Anomalous seismicity preceding smaller events cannot clearly be found by data of the Japan Meteorological Agency as shown Fig. 8. It is, however, not certain yet whether such earthquakes were not really preceded by anomalous seismicity.Our study requires further accumulation of examples from the viewpoint of ascertaining the existence of anomalous seismicity preceding earthquakes by observation network for small earthquakes.