Rupture directivity of the 25 November 2018 Taiwan Strait Mw5.8 earthquake and its tectonic implications
Rupture directivity of the 25 November 2018 Taiwan Strait Mw5.8 earthquake and its tectonic implications
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2018年11月25日台湾海峡Mw5.8地震破裂方向性及其构造意义
DOI：
10.1016/j.tecto.2021.228852
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发表时间：
2021
期刊：
影响因子：
2.9
通讯作者：
Xin Lin
中科院分区：
文献类型：
--
作者：
Shuofan Wang;Xiangfang Zeng;Min Xu;Yayun Zhang;Yong Zhou;Xing Wei;Xin Lin
台湾海峡位于活跃变形的台湾岛和稳定的华南克拉通之间。虽然台湾海峡东西两岸都发生过强震，其地震构造也相对较清楚，但海峡的地震风险和发震结构仍需要更多的研究。 2018年11月25日，海峡内部发生罕见的Mw5.8级中强地震，引发附近地区大范围地面震动。从地震资料波形反演可知，此次地震为一次大倾角走滑事件，两个节点面分别指向东西（EW）和南北（NS）方向。由于震中地区存在东西向和南北向的地图断层，需要进一步研究以确定破裂断层面。为了确定破裂断层面，我们分析了主震破裂方向性与震源与质心之间的相对位置。我们选择了几次M4+余震作为参考事件，并利用Pn走时差对参考地震进行了重新定位。然后，利用区域波形数据反演地震质心位置和震源参数。此后，我们通过拟合主震与参考地震之间乐夫波时移差的方位角变化，估计了主震破裂断层的走向和破裂长度。我们的结果表明，主震沿 NS 走向破裂，破裂长度约为 3.6–5.6 km。结合构造推断，发震断裂为东山隆起东部断裂（DSEF），1994年的事件可能促进了2018年Mw5.8级地震的发生。
Taiwan Strait is located between the actively deforming Taiwan Island and stable South China Craton. While strong earthquakes have occurred on the east and west sides of the Taiwan Strait and their seismotectonic are relatively well understood, the earthquake risk and seismogenic structure in the strait still need more investigations. On November 25, 2018, a rare moderately strong earthquake with a magnitude of Mw5.8 occurred inside the strait, and it caused broad ground motions in the near regions. From the waveform inversion of the seismic data, this earthquake is found to be a high-dip angle strike-slip event, with the two nodal planes striking east-west (EW) and north-south (NS) directions. As there are mapped faults striking EW and NS in the epicentral region, further studies are needed to determine the ruptured fault plane. To determine the ruptured fault plane, we analyzed the rupture directivity of the mainshock with the relative location between the hypocenter and the centroid. We chose several M4+ aftershocks as reference events and relocated the reference earthquakes with the Pn travel time difference. Then, we used regional waveform data to invert centroid location and source parameters of earthquakes. Thereafter, we estimated the strike of the mainshock ruptured fault and rupture length, via fitting the azimuthal variation of the Love wave time shift difference between the mainshock and the reference earthquakes. Our results showed that the mainshock ruptured along NS strike with the rupture length about 3.6–5.6 km. Combined with the tectonics, we inferred that the seismogenic fault is the Dongshan uplift eastern fault (DSEF) and the 1994 event may promote the occurrence of the 2018 Mw5.8 earthquake.