関東地方南部の地震活動

概要

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Based on seismic data and focal mechanism solutions, a study is made on the seismic activity in the southern part of Kwanto, central Japan, during the period from 1926 to 1968. In view of regularities of focal mechanism as well as a spatial distribution of major earthquakes, the area concerned in the present paper are divided into six blocks (cf. Fig. 5), and an interrelation of seismic activities among the six blocks are statistically tested. The tests suggest that the occurrence of earthquakes in each block is exclusive in time, and that the seismic activities in the blocks except zones 1 and 4 in Fig. 5 increase gradually year after year. A peculiar evidence is that only a few events were observed in the period concerned in the middle part of Boso Peninsula where an abnormal land upheaval of several centimeters were detected by means of geodetic surveys during the period from 1965 to 1969. It is also strange that the seismic activity is in a quite low level in the epicentral area for the great Kwanto earthquakes of 1923 in the past 43 years. In addition, a description is made the reliability of earthquake parameters given by the Japan Meteorological Agency and the earthquake detection capability of the seismological network of the Agency. The description will be useful in relevant people who conduct using the data given by the Agency.
社団法人東京地学協会の論文