首页|泸定Ms6.8地震发震机制研究——来自震前噪声成像和b值分布的共同约束

泸定Ms6.8地震发震机制研究——来自震前噪声成像和b值分布的共同约束

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2022年9月5日四川省甘孜州泸定县发生了 Ms6.8地震,打破了鲜水河断裂带东南段的大震"平静期",造成了重大自然灾害.清楚认识泸定地震震源区发震构造、地震活动性和应力状态对研究强震发震机制具有重要作用.本文利用震前在泸定地震震源区布设的50台短周期流动地震台阵观测资料及区域地震台网震相走时数据,分别采用背景噪声成像、双差定位和改进的b值成像技术,获得了震前震源区浅层高分辨率S波速度结构、地震空间分布及b值横向变化图像.结果揭示,泸定地震主震初始破裂起始于鲜水河断裂磨西段、具有高速异常和高应力特征的凹凸体内;主震西侧存在一条隐伏的正断型伴生分支断裂,5.0级的最大余震即发生在该断裂上;主震凹凸体的破裂同时造成了东南方向另一个较小高速凹凸体的破裂并形成密集余震群.由此可见,震源区跨断层高速异常"铆钉"结构和震前的高应力积累在整体上控制了泸定地震的发生和强余震活动.通过浅层高分辨率结构成像识别这种特殊的"铆钉"结构,同时通过b值成像识别高应力区,可有效评估断层的发震能力,对重点区域地震危险性研判具有极其重要的意义.
The seismogenic mechanism of the Luding Ms6.8 earthquake revealed from preseismic S-wave velocity structure and b-value distribution of the epicenter area
On 5 September 2022,an Ms6.8 earthquake occurred in Luding County,Garzê Prefecture,Sichuan Province,which broke a"quiet period"of large earthquakes in the southeast section of the Xianshuihe fault and caused a major natural disaster.The seismogenic structure,seismicity and stress state in the epicenter area of the Luding earthquake plays an important role in understanding the seismogenic mechanism of strong earthquake.In this paper,based on the seismic waveform recorded from 50 short-period seismic stations deployed in the Luding area before the earthquake and the seismic travel time data collected from the regional seismic networks,we investigated high-resolution S-wave velocity structure,spatial earthquake distribution and b-value variation images of shallow crust in the Luding area before the earthquake by ambient noise tomography,double-difference relocation and improved b-value imaging method,respectively.The results show that the mainshock rupture of the Luding earthquake initiated from an asperity with high-velocity anomaly and high stress characteristics in the Moxi segment of the Xianshuihe fault.On the west side of the mainshock,we revealed a hidden normal fault resulted from the largest M5.0 aftershock,which is concomitant branch fault within Xianshuihe Fault system.The mainshock ruptured both a dominant asperity and another smaller southeastern asperity with high-velocity,and caused clustered aftershocks there.These results indicate that the high-velocity"rivet"structures cross fault and high stress accumulation before the earthquake in the source area controlled the occurrences of the Luding mainshock as well as strong aftershocks in general.Identifying these special"rivet"structures through high-resolution structure imaging as well as high stress situation through b-value imaging can effectively evaluate the seismogenic capacity of faults,which is of great significance to seismic hazard assessment in key areas.

The Luding Ms6.8 earthquakeS-wave velocity structureb-value imagingHigh-velocity asperitySeismogenic mechanism

花茜、裴顺平、杨宜海、薛晓添、李磊、李佳蔚、刘翰林、刘巍

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中国科学院青藏高原研究所,青藏高原地球系统与资源环境国家重点实验室,北京 100101

陕西省地震局,西安 710068

中国科学院大学,北京 100049

云南大学,昆明 650091

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泸定Ms6.8地震 S波速度结构 b值成像 高速凹凸体 地震发震机制

国家自然科学基金国家自然科学基金青藏高原综合科学考察研究项目(第二次)国家重点研发计划陕西省自然基础研究计划

U2039203421303062019QZKK07082017YFC15003032022JQ-234

2024

10.6038/cjg2023R0700

地球物理学报
中国地球物理学会 中国科学院地质与地球物理研究所

地球物理学报

CSTPCD北大核心
影响因子：3.703
ISSN：0001-5733
年,卷(期)：2024.67(5)
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