Unusually deep Bonin earthquake of 30 May 2015: A precursory signal to slab penetration?,
Unusually deep Bonin earthquake of 30 May 2015: A precursory signal to slab penetration?,
复制标题
2015 年 5 月 30 日发生的异常深博宁地震：板片穿透的前兆信号？
DOI：
10.1016/j.epsl.2016.11.019
复制
发表时间：
2017
期刊：
影响因子：
--
通讯作者：
and J. Yoshimitsu
中科院分区：
文献类型：
--
作者：
Obayashi;M.;Y. Fukao;and J. Yoshimitsu
2015 年 5 月 30 日发生了 M7.9 地震，深度不寻常，深度为 680 公里，远离博宁岛弧南部明确的瓦达蒂-贝尼奥夫 (WB) 区域。在北部（小博宁北部），俯冲板片停滞在上、下地幔边界上方 660 公里深度处，其中 WB 区向前弯曲至近水平。向南（北马里亚纳），它穿过边界，西岸区域几乎垂直向下延伸到边界。因此，博南板片南部可视为处于板片停滞到渗透的过渡状态。研究表明，这种转变在博宁板块南部的北半部内迅速发生，鞋状构造的停滞板块的脚跟部分撞击了明显凹陷的 660 公里不连续面。主震和余震发生在这个跟部，它们在垂直方向上大致平行于它们的最大压缩轴。在这里，WB带地震的压缩轴倾角从东侧到西侧在板片厚度上以及从北侧到南侧沿板片走向快速变化，表明鞋形板片中下倾压缩轴的快速切换。与 WB 区地震活动相关的弹性变形是通过将其视为板片变形过程的一个组成部分来计算的。随着这种变形，跟部相对于足弓部分加深，并被近垂直压缩和近水平拉伸，这种趋势与跟部渐进下降的想法一致，其中接近垂直的压缩应力逐渐累积，产生像2015年事件那样的孤立冲击，并最终引发板坯穿透。
An M7.9 earthquake occurred on 30 May 2015 at an unusual depth of 680 km downward and away from the well-defined Wadati–Benioff (WB) zone of the southern Bonin arc. To the north (northern Bonin), the subducted slab is stagnant above the upper–lower mantle boundary at 660-km depth, where the WB zone bends forward to sub-horizontal. To the south (northern Mariana), it penetrates the boundary, where the WB zone extends near-vertically down to the boundary. Thus, the southern Bonin slab can be regarded as being in a transitional state from slab stagnation to penetration. The transition is shown to happen rapidly within the northern half of the southern Bonin slab where the heel part of the shoe-like configured stagnant slab hits the significantly depressed 660-km discontinuity. The mainshock and aftershocks took place in this heel part where they are sub-vertically aligned in approximate parallel to their maximum compressional axes. Here, the dips of the compressional axes of WB zone earthquakes change rapidly across the thickness of the slab from the eastern to western side and along the strike of the slab from the northern to southern side, suggesting rapid switching of the downdip compression axis in the shoe-shaped slab. Elastic deformation associated with the WB zone seismicity is calculated by viewing it as an integral part of the slab deformation process. With this deformation, the heel part is deepened relative to the arch part and is compressed sub-vertically and stretched sub-horizontally, a tendency consistent with the idea of progressive decent of the heel part in which near-vertical compressional stress is progressively accumulated to generate isolated shocks like the 2015 event and eventually to initiate slab penetration.