4. The Mechanism of Some Deep and Intermediate Earthquakes in the Region of Japan

The result of the investigation of the patterns of S waves recorded at large distances from the foci of 7 intermediate and deep earthquakes, which occurred in and near Japan, confirms the validity of the double couple hypothesis of earthquake mechanism forthese shocks. The study of the S waves of 39 additional shocks of the region recorded at De Bilt gives support to the hypothesis. The amplitude ratios of the P and S waves of these earthquakes seem to indicate that the radii of the focal spheres of earthquakes of magnitudes 6Va to 7.8 are of the order of 10 to 50km.日本附近に起こつた7個の稍深発および深発地震について,遠距離の地点におけるS波の運動の向きの分布を調べて,これらの地震のメカニズムがdouble couoleの仮説によつて説明できることを示した.またDe Biltにおいて記録された同地域の39個の地震のS波を調べて同じ仮説が成り立つことがわかつた.マグニチュードが61/2から7.8の範囲内にあるこれらの地震のP波とS波の振幅の比から,メカニズムのモデルとして用いた震源球の半径は10kmから50km位であると推定される