著者

Kanamori Hiroo

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.49, no.1-3, pp.13-18, 1971-09-30

---

The fault parameters of the Great Kanto earthquake of September 1, 1923, are determined on the basis of the first-motion data, aftershock area, and the amplitude of surface waves at teleseismic stations. It is found that the faulting of this earthquake is a reverse right-lateral fault on a plane which dips 34° towards N20°E. The auxiliary plane has a dip of 80° towards S55°E. This means that the foot-wall side moves approximately north-west with respect to the hanging wall side. The strike of the fault plane is almost parallel to that of the Sagami trough, and the slip direction is more or less perpendicular to the trend of the Japan trench. This earthquake is therefore considered to represent a slippage between two crustal blocks bounded by the Sagami trough. A seismic moment of 7.6×1027 dyne-cm is obtained. If the fault dimension is taken to be 130×70 km2, the average slip on the fault plane and the stress drop are estimated to be 2.1m and 18 bars respectively. This slip is about 1/3 of that estimated from geodetic data. This discrepancy may indicate an existence of a pre-seismic deformation which did not contribute to the seismic wave radiation, but the evidence from other observations is not very firm.|関東地震の断層パラメターをP波の初動分布と長周期表面波の振幅からきめた.その結果,この地震はN20°Eの方向に34°傾いた面上での右ずれ・逆断層であらわされることがわかつた.断層面の大きさを130×70km2とすると,断層面上でのすべりは約2m, stress dropは18バールである.断層上でのすべりのむきが相模troughの走向に平行で,日本海溝に垂直であり,また震源が浅く(地殻内)かつ日本海溝から遠くはなれていることを考ると,関東地震は海と陸のリゾスフィアの相互作用の直接の結果とは考えにくい.むしろ,この地震は海と陸のリゾスフィアの相互作用によつて2次的に起つた,相模troughを境とする二つの地塊のずれによるものであると解釈できる.地殻変動の大きさから推定されているすべりの大きさは7mであるが,これは表面波の振幅から推定された値2mよりはるかに大きい.この違いは種々の誤差を考慮にいれてもなお有意義と思われる.このくいちがいは,全体の地殻変動量のうち2分以内の時定数をもつもののみが地震波の発生に関与したと考えれば説明できる.