关键词: 千岛, 鄂霍次克海, 地震, 震源机制, 应力

Abstract: The distribution of earthquakes of M_b≥4.0 from 1971 to 1982 were studied using the data from I.S.C.; 43 focal mechanisms were obtained using the first motions of compressional wave from I.S.C and the network of the Chinese earthquake observatories. The earthquakes are distributed mainly in an arc-like belt along Kuril islands. There is an obvious Benioff zone beneath Kuril islands and Kamchatka. The depth into which the Benioff zone extends is different in different parts of the Benioff zone. The maximum depth is about 619km and the minimum depth is about 180km. The dip direction of the Benioff zone is about NW55° and the dip angle is about 45°.The P axes of focal mechanisms for earthquakes in the crust in both sides of the trench are in the NW direction and nearly horizontal, reflecting the compression from the Pacific plate. The stress state on the subduction zone varies with depth: Above-114km, the T axes of focal mechanisms are nearly consistent with the direction of subduction; in the range of depths from 114km to 175km, the focal mechanisms are divided into two groups: one is that the T axes coincide with the direction of subducting and P axes are nearly horizontal, another is that the P axes coincide with the direction of subducting and T axes are nearly horizontal: In the range of depths from 175km to 220km, the P axes are coincident with the direction of subduction; From 320km to 440km, P and T axes are not as good in gathering as in other depths, but the P axes appear to be close to the direction of subducting; In the depths from 515km to 619km, the P axes are coincident with the direction of subducting. The reason for the stress state was also discussed.

Key words: Kuril Islands, The sea of Okhotsk, Earthquake mechanism, Stress