千岛—鄂霍次克海地区的地震分布、震源机制及应力状态

利用1971年1月至1982年12月的地震资料,研究了千岛岛弧地区的地震分布及震源机制解,进而讨论了贝尼奥夫带的形态及应力状态。地震分布于沿海沟展布的NE向的弧形带上,除地壳内地震外,形成明显的贝尼奥夫带,贝尼奥夫带最深达619公里,两侧较浅,少于200公里,倾向近于NW55°,倾角为45°。地壳内的压应力轴位于NW方向,且接近于水平,反映了太平洋板块的挤压;俯冲带上应力轴随深度变化:114公里以上的T轴沿俯冲方向,114公里至175公里震源机制解分为两组,T轴沿俯冲方向和P轴沿俯冲方向;320公里至440公里范围内P轴有接近俯冲方向的趋势,但较为分散;515公里以下P轴相当集中,且沿俯冲方向。本文对这种应力分布的成因进行了讨论

DISTRIBUTION AND FOCAL MECHANISM OF EARTHQUAKES AND STRESS STATE ON KURIL ISLANDS AND SEA OF OKHOTSK

The distribution of earthquakes of Mb≥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