龙锋^1,,
祁玉萍¹,
易桂喜^1,2,,,
吴微微^1,2,
王光明³,
赵小艳³,
彭关灵³
1. 四川省地震局, 成都 610041
2. 中国地震局成都青藏高原地震研究所, 成都 610041
3. 云南省地震局, 昆明 650224

基金项目: 国家重点研发项目（2018YFC150330501）和国家自然科学基金（41574047）共同资助


详细信息

作者简介: 龙锋, 高级工程师, 主要从事地震预测、地震定位、速度结构反演等方面的研究.E-mail: icy1111@163.com

通讯作者: 易桂喜, 博士, 研究员, 主要从事地震预报方法研究及壳幔速度结构反演等方面的研究.E-mail: yigx64@163.com

中图分类号: P315

收稿日期:2021-06-19
修回日期:2021-07-05
上线日期:2021-08-10

Relocation of the M_S6.4 Yangbi earthquake sequence on May 21, 2021 in Yunnan Province and its seismogenic structure analysis

LONG Feng^1,,
QI YuPing¹,
YI GuiXi^1,2,,,
WU WeiWei^1,2,
WANG GuangMing³,
ZHAO XiaoYan³,
PENG GuanLing³
1. Sichuan Earthquake Agency, Chengdu 610041, China
2. Chengdu Institute of the Tibetan Plateau Earthquake Research, China Earthquake Administration, Chengdu 610041, China
3. Yunnan Earthquake Agency, Kunming 650224, China


More Information

Corresponding author: YI GuiXi,E-mail:yigx64@163.com

MSC: P315

--> Received Date: 19 June 2021
Revised Date: 05 July 2021
Available Online: 10 August 2021


摘要
摘要:本文利用云南区域地震台网提供的震相报告，采用"多阶段定位"方法，对2021年5月21日云南漾濞M_S6.4地震序列的震源位置进行了重新定位.选取序列中13次具有高信噪比宽频带波形记录的M_S≥4.0地震事件，应用CAP波形反演方法，获取了这些事件的震源机制解和震源矩心深度.结果显示，漾濞地震序列震中距离NE侧的维西—乔后断裂约3~10 km，余震区长轴呈NW-SE向展布，长约22 km，震源优势分布深度为4~8 km，反映本次地震发生在上地壳浅部.地震分布北西窄、南东宽的分段特征明显，北西段地震更浅、更密集，南东段事件更深、更分散且存在向S偏转的现象.余震区不同位置的短轴剖面分析表明，发震构造倾向SW，南东段倾角缓于北西段.北西段还存在规模较小的NE向共轭断裂，长度约5 km.5月18日开始的前震自余震区中段向NW逐级迁移扩展，前震序列密集且存在相互触发，符合前震发生的级联模式.主震位于余震密集区的NW端，表明其具备SE向单侧破裂特征.多数4级以上地震的震源机制解都具有与序列长轴走向一致的NW-SE走向、高倾角SW倾向节面；基于震源机制解反演获得的区域构造应力场显示，发震构造受NNW-SSE向近水平主压应力作用发生右旋走滑运动，揭示主发震断层产状和错动类型与维西—乔后断裂基本一致.因此，可初步判定发震构造为维西—乔后断裂的平行伴生断裂，这一构造的形成可能与川滇块体SE向滑移和滇西南块体的顺时针旋转有关.
关键词: 漾濞地震/
地震定位/
震源机制解/
发震构造

Abstract:In this paper, we relocated the M_S6.4 Yangbi earthquake sequence in Yunnan province by the "multi-stage" method and the phase arrival data from the Yunnan regional seismic network. The focal mechanism solutions of 13 M_S≥4.0 events were calculated by the CAP program. We found that the sequence is about 3~10 km away from the nearest known Weixi-Qiaohou fault, and the long-axis of the aftershock events is about 22 km striking NW-SE, with its dominant focal depth is 4~8 km, reflecting the Yangbi earthquake occurred in the shallow part of the upper Crust. Earthquakes along the northern segment of the aftershock area are relatively shallow and dense, while along the southern segment earthquakes are deeper and more dispersed and deflected to the south. Different short-axis cross-sections reveal that the seismogenic structure is dipping towards SW with a gentler angle for the SE segment and steeper angle for the NW segment. We identified two small-scale NE-striking conjugate faults (about 5 km long) in the northern part of the sequence. The foreshocks on May 18 propagated gradually from the center towards NW where the mainshock is located. Since the foreshock sequences were dense and triggered by each other, we thus concluded a cascade mode of the foreshock occurrence. The main shock was located in the NW end of the aftershock intensive area, which indicated that it had the characteristics of SE-trending unilateral rupture. The focal mechanism solutions of most M_S≥4.0 events have NW-SE striking steep nodal planes, consistent with the long axis of the aftershock distribution. The stress inversion results revealed that the seismogenic structure is affected by the NNW-SSE striking nearly horizontal principal compressive stress, which is consistent with the fault occurrence and dislocation type of the adjacent Weixi-Qiaohou fault. It can be preliminarily determined that the seismogenic structure is a parallel secondary structure of Weixi-Qiaohou fault. The formation of this structure may be related to the SE escape of the active Sichuan-Yunnan block and the clockwise rotation of Southwest Yunnan block.
Key words:Yangbi earthquake/
Earthquake location/
Focal mechanism solution/
Seismogenic structure



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