李赫, 董一兵, 王熠熙, 吴博洋, 彭钊. 2020: 永清MS4.3地震和廊坊MS3.0地震的发震构造研究. 地震学报, 42(4): 392-405. DOI: 10.11939/jass.20200021
引用本文: 李赫, 董一兵, 王熠熙, 吴博洋, 彭钊. 2020: 永清MS4.3地震和廊坊MS3.0地震的发震构造研究. 地震学报, 42(4): 392-405. DOI: 10.11939/jass.20200021
Li He, Dong Yibing, Wang Yixi, Wu Boyang, Peng Zhao. 2020: Seismogenic structure of Yongqing MS4.3 and Langfang MS3.0 earthquakes. Acta Seismologica Sinica, 42(4): 392-405. DOI: 10.11939/jass.20200021
Citation: Li He, Dong Yibing, Wang Yixi, Wu Boyang, Peng Zhao. 2020: Seismogenic structure of Yongqing MS4.3 and Langfang MS3.0 earthquakes. Acta Seismologica Sinica, 42(4): 392-405. DOI: 10.11939/jass.20200021

永清MS4.3地震和廊坊MS3.0地震的发震构造研究

Seismogenic structure of Yongqing MS4.3 and Langfang MS3.0 earthquakes

  • 摘要: 基于首都圈数字地震台网的宽频带资料,首先采用CAP方法确定了永清MS4.3地震和廊坊MS3.0地震的震源机制解:永清地震节面Ⅰ的走向、倾角和滑动角分别为52°,62°和−140°,节面Ⅱ的走向、倾角和滑动角分别为300°,55°和−35°;廊坊地震节面I的走向、倾角和滑动角分别为48°,57°和−147°,节面Ⅱ的走向、倾角和滑动角分别为299°,63°和−38°。两次地震的震源机制解较为一致,推测它们可能具有相同的发震断层。利用近震转换波获得两次地震的震源深度,分别为19 km和13 km。利用双差法对两次地震的主余震进行重新定位,结果显示:两个地震序列的震中均呈NE向分布,余震震源深度均浅于主震震源深度,震源深度分别集中在17—20 km和12—13 km范围内,两个序列的短轴剖面揭示了震源分布均呈现倾向SE,倾角陡立的特点。将地震序列的分布与震源机制解的结果进行对比,认为两个序列的水平展布方向与其对应的主震震源机制解中节面Ⅰ的走向比较接近,深度分布的高倾角特征也与节面Ⅰ比较相似,因此认为发震断层面均为节面Ⅰ。通过将震源机制解中节面Ⅰ的参数和地震序列的分布与区域活动断层的产状性质进行比较,取得了一些关于发震构造和地震成因的重要认识:① 永清MS4.3地震和廊坊MS3.0地震的发震构造不是上地壳的先存正断裂−河西务断裂,不排除与中下地壳的新生构造或深大断裂有关;② 永清、廊坊地震发生在13—19 km深度上,结合地壳结构、断裂构造以及区域流变结构等资料,推测该深度范围可能是廊固凹陷的壳内脆性−韧性转换区域,是地震孕育和发生的有利构造部位。

     

    Abstract: On February 12, 2018 and February 3, 2019, the MS4.3 and MS3.0 earthquakes occurred in Yongqing county and Langfang city, Hebei Province, and the two epicenters were less than 10 km apart. In order to study the seismogenic structure of these two earthquakes, based on the wide-band data of the digital seismic network of the Capital Circle, the focal mechanism solutions of the two earthquakes were determined by the CAP method first. For the Yongqing earthquake, the strikes, dip angle and rake angle of nodal plane I are 52°, 62° and −140° separately; and the strikes, dip angle and rake angle of nodal plane II are 300°, 55° and −35° separately; For the Langfang earthquake, the strike, tilt angle and slide angle of nodal plane I are 48°, 57° and −147° separately, and the direction, inclination and sliding angle of joint II are 299°, 63° and −38° separately. The focal mechanism solutions of the two earthquakes are relatively consistent, hence it is speculated that they may have the same seismogenic fault. The source depths of the two earthquakes obtained by converted waves of near earthquakes are 19 km and 13 km, respectively. The double-difference method was used to relocate the main and aftershocks of the two earthquakes. The results show that the epicenters of the two earthquake sequences are NE-directed, and the aftershocks all occur above the main shock. The focal depths are respectively concentrated in the range of 17−20 km and 12−13 km. Besides, the short-axis profiles of the two sequences reveal that the source distributions are characterized by SE tendency and steep dip angle. By comparing the seismic sequence distribution with the focal mechanism solutions, it found that the horizontal distribution direction of thesequences ars closer to the trend of the joint surface I in the focal mechanism solutions of the two earthquakes, and the high dip angle characteristics of the depth distribution are also similar to the joint surface I. Therefore, the seismogenic fault plane is considered to be nodal plane I. By comparing the parameters of nodal I from the focal mechanism solutions, the distribution of seismic sequences and the attitude properties of regional active faults, some important knowledge about the seismogenic structure and the origin of earthquakes was obtained: ① The seismogenic structure of the Yongqing MS4.3 earthquake and the langfang MS3.0 earthquake are not the pre-existing normal fault of the upper crust−the Hexiwu fault, and it may relate to the nascent structure of the middle and lower crust or deep faults. ② The Yongqing and Langfang earthquakes occurred at a depth of 13−19 km. Synthesize the crustal structure, fault structure and regional rheological structure, it is speculated that this depth range may be the intracrustal brittle-ductile transition area in the Langgu depression, which is favorable structural part for earthquake preparation and occurrence.

     

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