| 2022年1月8日青海门源MS6.9地震序列重定位和震源机制解研究 |
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| 引用本文： | 许英才,郭祥云,冯丽丽.2022年1月8日青海门源MS6.9地震序列重定位和震源机制解研究[J].地震学报,2022,44(2):195-210. |
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| 作者姓名： | 许英才 郭祥云 冯丽丽 |
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| 作者单位： | 1.中国银川 750001 宁夏回族自治区地震局 |
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| 基金项目： | 中国地震局震情跟踪定向工作任务;国家重点研发计划;宁夏自然科学基金项目;青海省科技厅基础研究计划;中国地震局地球所基本科研业务费专项 |
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| 摘 要： | 2022年1月8日青海省海北州门源县发生MS6.9地震，震后产生了长约22 km的地表破裂带，青海、甘肃和宁夏等多地震感强烈。本文基于区域地震台网资料，通过多阶段定位方法对门源MS6.9地震早期序列（2022年1月8日至12日）进行了重定位，并利用gCAP方法反演了主震和MS≥3.4余震的震源机制和震源矩心深度，计算了现今应力场体系在门源MS6.9地震震源机制两个节面产生的相对剪应力和正应力。结果表明:门源MS6.9地震的初始破裂深度为7.8 km，震源矩心深度为4 km，地震序列的优势初始破裂深度主要介于7—8 km之间，而MS≥3.4余震的震源矩心深度为3—7 km；该地震序列的震源深度剖面显示震后24个小时内的地震序列长度约为25 km，与地表破裂带的长度大体一致，整体地震序列长度约为30 km，其中1月8日MS6.9主震和MS5.1余震位于余震区西段，1月12日MS5.2余震位于余震区东段。2022年1月8日门源MS6.9主震的震源机制解节面Ⅰ为走向290°、倾角81°、滑动角16°，节面Ⅱ为走向197°、倾角74°、滑动角171°，根据余震展布的总体趋势估计断层面走向为290°，表明此次地震为近乎直立断层面上的一次左旋走滑型事件；MS≥3.4余震的震源机制解显示这些地震主要为走滑型地震，P轴走向从余震区西段到东段之间大体呈现NE向到EW向的变化。现今应力场体系在门源MS6.9主震震源机制解节面Ⅰ上产生的相对剪应力为0.638，而在节面Ⅱ上的相对剪应力为0.522，表明这两个节面均非构造应力场的最大释放节面，这与2016年门源MS6.4地震逆冲型震源机制为构造应力场的最优释放节面有着明显差异。结合地质构造、震源机制和余震展布，2022年1月8日门源MS6.9主震的发震构造可能为冷龙岭断裂西段，其地震断层错动方式为左旋走滑。根据重定位结果、震级-破裂关系以及剪应力结果，本文认为门源地区存在一定的应力积累且应力未得到充分释放，该地区仍存在发生强震的危险。
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| 关 键 词： | 门源MS6.9地震 重定位 震源机制 发震构造 滑动特性 |
| 收稿时间： | 2022-01-18 |
Relocation and focal mechanism solutions of the MS6.9 Menyuan earthquake sequence on January 8, 2022 in Qinghai Province |
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| Xu Yingcai,Guo Xiangyun,Feng Lili.Relocation and focal mechanism solutions of the MS6.9 Menyuan earthquake sequence on January 8, 2022 in Qinghai Province[J].Acta Seismologica Sinica,2022,44(2):195-210. |
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| Authors: | Xu Yingcai Guo Xiangyun Feng Lili |
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| Institution: | 1.Earthquake Agency of Ningxia Hui Autonomous Region，Yinchuan 750001，China2.Institute of Geophysics，China Earthquake Administration，Beijing 100081，China3.Qinghai Earthquake Agency，Xining 810001，China |
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| Abstract: | On January 8, 2022, an earthquake with MS6.9 occurred in Menyuan County, Haibei Prefecture of Qinghai Province. The earthquake ruptured a nearly 22 km long surface fracture zone and strong tremors were felt through the regions of Qinghai, Gansu and Ningxia regions. In this paper, the early events of the MS6.9 Menyuan earthquake sequence from January 8 to 12, 2022 were relocated by multi-step locating method. Meanwhile, the focal mechanisms and focal depths of the main shock and MS≥3.4 aftershocks were calculated by gCAP method. Based on focal mechanism result of the main shock, the relative shear stress and normal stress on the two nodal planes of the focal mechanism solutions were also calculated under the existing stress field system. The result indicates that the initial rupture depth of MS6.9 Menyuan main shock was 7.8 km, and the centroid depth was 4 km. The dominant initial rupture depths of early earthquake sequence were mainly between 7 km and 8 km, while the centroid depths of MS≥3.4 aftershocks varied between 3 km and 7 km. The focal depth profile shows that the sequence length within 24 hours after the main shock was about 25 km, which was roughly consistent with the length of the surface rupture zone, and the overall sequence length was about 30 km. The MS6.9 main shock and MS5.1 aftershocks on January 8 were located in the western part of the aftershock region, and the MS5.2 earthquake on January 12 was located in the eastern part of the aftershock region. The focal mechanism solution of the MS6.9 main shock was strike 290°, dip 81°, rake 16° for the nodal plane Ⅰ , and strike 197°, dip 74°, rake 171° for the nodal plane Ⅱ . Based on the spatial distribution of aftershocks, it is estimated that the strike of the fault plane is 290o, indicating that the earthquake is a left-lateral strike slip event on a nearly vertical fault plane. The results of focal mechanism solutions of MS≥3.4 aftershocks show that these earthquakes were mainly strike-slip, and from the west to the east of the aftershock region the P-axis azimuths varied from NE to EW. Under the current stress field system, the relative shear stress generated on the nodal plane Ⅰ of focal mechanism of the MS6.9 Menyuan earthquake is 0.638, while on the nodal plane Ⅱ is 0.522. The two nodal planes of focal mechanism are not the maximum released nodal plane of the tectonic stress field, which is obviously different from the thrust focal mechanism of the MS6.4 Menyuan earthquake in 2016, which is the optimal released nodal plane of tectonic stress field. Combined with the geological structure, focal mechanisms and aftershock distribution, the seismogenic structure of MS6.9 Menyuan earthquake on January 8, 2022 may be the western segment of Lenglongling fault, and its seismic dislocation mode is left-lateral strike-slip. According to the results of relocation, the magnitude-rupture relationship and the shear stress, it is concluded that there is a certain stress accumulation and stress has not been fully released in Menyuan area, and the risk of strong earthquakes still exists in this area. |
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