Crustal structure and seismicity beneath the forearc off northeastern Japan
Crustal structure and seismicity beneath the forearc off northeastern Japan
复制标题
日本东北部弧前下方的地壳结构和地震活动
DOI：
10.1029/94jb01337
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发表时间：
1994
影响因子：
--
通讯作者：
A. Nishizawa
中科院分区：
文献类型：
--
作者：
K. Suyehiro;A. Nishizawa
本文利用日本海沟（38.5°N以北）的海洋地震学和其它资料，推断了俯冲板块结构、地震活动性和震源机制，特别是俯冲板块与两个相互作用板块之间沿着界面孕震区的关系。利用多道地震资料，考虑地震相对振幅特征，约束浅层结构，改进了以往的海底地震折射（OBS）地壳模型。在这些模型中的波速不连续被解释为覆盖板块的地壳和俯冲太平洋板块地壳的接触区。它的倾角增加到约7°，向陆110公里的海沟轴。深海阶地下方需要大幅增加，以达到东北东海岸下方25°的明确角度。通常在正常海洋下观察到的第2层内的大的波速梯度似乎在约10公里深度的内沟斜坡下消失。在覆盖板块内，P波速度为0.66 km/s的明显脆性材料可以在距离海沟轴35 km处找到。根据OBS地震活动和大事件分析，板间低角度逆冲事件孕震带的上限约为15 km深度。为了确定相互作用板块的地震耦合，必须研究上覆板块地壳的强度和俯冲沉积物的特性。
Marine seismological and other data in the Japan Trench area (north of 38.5°N) were used to infer the relation of subducting plate structure, seismicity, and focal mechanisms especially at the aseismic to seismogenic zone along the interface between the two interacting plates. Previous crustal models from ocean bottom seismographic refraction (OBS) surveys were improved by taking into account the relative seismic amplitude characteristics and constraining the shallow structure using multichannel seismic data. A wave speed discontinuity in these models is interpreted to be the contact zone of the crust of the overriding plate and the subducting Pacific plate crust. Its dip angle increases to about 7°, 110 km landward of the trench axis. A large increase beneath the deep sea terrace is required to reach the well-defined angle of 25° beneath the Tohoku east coast. A large wave speed gradient within layer 2, commonly observed under normal oceans, seems to vanish beneath the inner trench slope at about 10-km depth. Within the overriding plate, apparently brittle material with a P wave speed of ∼6 km/s can be found as near as 35 km from the trench axis. The upper limit of the seismogenic zone of interplate low-angle thrust events is about 15-km depth from OBS seismicity and large-event analyses. Both the strength of the crust of the overriding plate and the characteristics of subducting sediments must be investigated to define the seismic coupling of interacting plates.