2019年黄海ML4.6地震序列的震源机制和发震构造

Focal mechanism and seismogenic structure of the 2019 Yellow Sea M_L4.6 earthquake sequence

2019年黄海ML4.6地震序列发生在NW向苏北—滨海断裂带附近,历史上该断裂带附近曾多次发生破坏性地震。为了判断此次地震序列的发生是否与苏北—滨海断裂带活动有关,本文基于黄海ML4.6地震震中附近400 km范围内的测震台站记录,采用CAP方法计算了此次黄海地震序列中ML4.6和ML4.1地震的深度和震源机制解参数,并使用双差定位方法对该地震序列进行了重新定位。研究结果显示:2019年12月8日黄海ML4.6和12日黄海ML4.1地震的震源深度分别为20 km和21 km,位于发震区域的脆韧转换带内;黄海ML4.6地震震源机制解节面Ⅰ的走向、倾角、滑动角分别为123°,74°和61°,节面Ⅱ的走向、倾角、滑动角分别为6°,33°和149°;黄海ML4.1地震震源机制解节面Ⅰ的走向、倾角、滑动角分别为135°,77°和32°,节面Ⅱ的走向、倾角、滑动角分别为37°,59°和165°。两次地震的震源机制解节面参数与苏北—滨海断裂带的几何参数并不一致,表明此次黄海地震序列的发生与苏北—滨海断裂带的主断裂活动没有直接关系。黄海地震序列震中的重新定位结果显示该地震序列呈NW向分布。由上述反演所获的两次黄海地震的震源机制和地震序列的重新定位结果推测,黄海ML4.6和ML4.1地震的破裂方向可能为NW向,黄海ML4.6地震序列可能是发生在区域壳内脆韧转换带的左旋走滑地震事件。

The 2019 Yellow Sea M_L4.6 earthquake sequence occurred near the NW-trending Subei-Binhai fault zone in the Yellow Sea,where occurred many destructive earthquakes in history.In order to determine whether the Yellow Sea earthquake sequence induced by the Subei-Binhai fault zone,we used the digital waveforms of seismic network within 400 km of the epicenter of M_L4.6 mainshock,carried out inversion for the focal depth and mechanism of the Yellow Sea M_L4.6 earthquake on 8 December 2019 and Yellow Sea M_L4.1 earthquake on 12 December 2019 with the CAP method,and then relocated the Yellow Sea earthquake sequence using the HypoDD method.Our result shows that the focal depths of the Yellow Sea M_L4.6 and M_L4.1 were 20 km and 21 km,suggesting that the two events occurred in the brittle-ductile transition zone within the seismogenic region.For the Yellow Sea M_L4.6 event,the strike,slip and rake are 123°,74°,and 61° for nodal plane Ⅰ,and those are 6°,33°,149° for nodal plane Ⅱ,respectively.For the Yellow Sea M_L4.1 earthquake,the strike,dip and rake are 135°,77° and 32° for nodal plane Ⅰ,and those are 37°,59° and 165° for the nodal plane Ⅱ,respectively.The nodal parameters of source mechanism for the two events are inconsistent with the geometric parameters of the Subei-Binghai fault zone,indicating that the Yellow Sea earthquake sequence has no direct relationship with the main fracture of Subei-Binhai fault zone.The relocation for Yellow Sea earthquake sequence shows that M_L4.6 earthquake sequence distributed in NW direction.According to the focal mechanisms from inversion and the relocation of the earthquake sequence,we deduced that the M_L4.6 and M_L4.1 earthquakes ruptured in NW direction,and the Yellow Sea M_L4.6 earthquake sequence is a left-lateral slip event induced by northwestward shearing rupture under tectonic stress field in the brittle-ductile transition zone.