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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Detailed structures of the subducted Philippine Sea plate beneath northeast Taiwan: A new type of double seismic zone
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Detailed structures of the subducted Philippine Sea plate beneath northeast Taiwan: A new type of double seismic zone

机译：台湾东北部俯冲菲律宾海板块的详细结构：一种新型的双重地震带

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We studied the detailed structure of the subducted Philippine Sea plate beneath northeast Taiwan where oblique subdction, regional collision, and back arc opening are all actively occurring. Simultaneous inversion for velocity structure and earthquake hypocenters are performed using the vast, high-quality data recorded by the Taiwan Seismic Network. We further supplement the inversion results with earthquake source parameters determined from inversion of teleseismic P and SH waveforms, a critical step to define the position of plate interface and the state of strain within the subducted slab. The most interesting feature is that relocated hypocenters tend to occur along a two-layered structure. The upper layer is located immediately below the plate interface and extends down to 70-80 km at a dip of 40 deg - 50 deg. Below approximately 100 km, the dip increases dramatically to 70 deg-80 deg. The lower layer commences at 45-50 km and stays approximately parallel to the upper layer with a separation of 15 +- 5 km in between down to 70-80 km. Below that the separation decreases and the two layers seem to gradually merge into one Wadati-Benioff Zone. We propose to term the classic double seismic zones observed beneath Japan and Kuril as "type I" and that we observed as "type II", respectively. A global survey indicates that type II double seismic zones are also observed in New Zealand near the southernmost North Island, Cascadia, just north of the Mendocino triple junction, and the Cook Inlet area of Alaska. All of them are located near the termini of subducted slabs in a tectonic setting of oblique subduction. We interpret the seismogenesis of type II double seismic zones as reflecting the lateral compressive stress between the subducted plate and the adjacent lithosphere (originating from oblique subduction) and the downdip extension (from slab pulling force). The upper seismic layer represents seismicity occurring in the upper crust of a subducted plate and/or along the plate interface, whereas the lower layer is associated with events in the uppermost mantle.
机译：我们研究了台湾东北部俯冲菲律宾海板块的详细结构，在这些俯冲板块，区域碰撞和反弧打开都在积极地发生。利用台湾地震台网记录的大量高质量数据对速度结构和地震震源进行同时反演。我们进一步用反震P和SH波形反演确定的震源参数补充反演结果，这是定义板界面位置和俯冲板内应变状态的关键步骤。最有趣的特征是重定位的震源往往沿着两层结构发生。上层位于板块界面的正下方，并以40度-50度的倾角向下延伸至70-80公里。在大约100公里以下，倾角急剧增加到70度至80度。下层开始于45-50 km，并保持与上层大致平行，相隔15±5 km，下至70-80 km。在此之下，分离减小，并且两层似乎逐渐合并为一个Wadati-Benioff区。我们建议将在日本和千岛下观测到的经典双重地震带分别称为“ I型”和“ II型”。一项全球调查表明，在新西兰最北端的卡斯卡迪亚附近，门多西诺三重交界处以北以及阿拉斯加的库克湾地区，也观察到了II型双重地震带。它们全部位于俯冲板块构造环境中俯冲板块的末端附近。我们将II型双地震带解释为反映了俯冲板块与相邻岩石圈之间的侧向压应力（源于斜向俯冲）和下倾延伸（源于平板拉力）。上地震层表示发生在俯冲板的上地壳和/或沿板界面的地震活动，而下层则与最上地幔中的事件有关。

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