38.Space Distribution of Earthquake Hypocentres in the Kivanto District.

The space distribution of the hypocentres of earthquakes that occurred in the Kwanto District within the last 12 years was statistically investigated. As is well known, the epicentres of earthquakes in this district are most closely distributed in two regions, namely, the northern part of Tokyo Bay and the region along the rivers Kinugawa and Tonegawa. Generally speaking, earthquakes are most frequent from depth of from 70 to 80km in the former region, and from depth of from 40 to 50km in the latter region, as already pointed out by Dr. T. Kodaira. The writer found however that, in the last 5 years (1931～1935), there were hardly any hypocentres beneath 60km in the former region, whereas in the preceding 7 years (1924～1930) they were most frequent from depth of from 70 to 80km in the same region. This fact may be regarded as showing that the instability caused in the lower part of the earth\u27s crust as the result of the Kwanto Earthquake of 1923 is gradually diminishing