曾宪伟^1,,
闻学泽^2,3,,,
龙锋³
1. 宁夏回族自治区地震局, 银川 750001
2. 中国地震局地质研究所, 地震动力学国家重点实验室, 北京 100029
3. 四川省地震局, 成都 610041

基金项目: 地震科技星火计划项目（XH18053Y）、宁夏自然科学基金项目（NZ14228）和国家自然科学基金（41604015）联合资助


详细信息

作者简介: 曾宪伟, 男, 高级工程师, 主要从事地震重新定位和震源机制解方面的研究.E-mail:zeng_xw@126.com

通讯作者: 闻学泽, 男, 研究员, 主要从事地震地质与地震中-长期危险性研究.E-mail:wenxueze@ies.ac.cn

中图分类号: P315

收稿日期:2018-10-19
修回日期:2019-03-11
上线日期:2019-12-05

Relocating the mainshock and M_L ≥ 3.0 aftershocks of the 2017 Jiuzhaigou sequence using first arriving P-phase only and reanalyzing the seismogenic structure

ZENG XianWei^1,,
WEN XueZe^2,3,,,
LONG Feng³
1. Earthquake Agency of Ningxia Hui Autonomous Region, Yinchuan 750001, China
2. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Agency, Beijing 100029, China
3. Earthquake Agency of Sichuan Province, Chengdu 610041, China


More Information

Corresponding author: WEN XueZe,E-mail:wenxueze@ies.ac.cn

MSC: P315

--> Received Date: 19 October 2018
Revised Date: 11 March 2019
Available Online: 05 December 2019


摘要
摘要:综合利用区域台站和流动台站（近台）的记录，基于初至P震相重新测定了2017年九寨沟序列M_S7.0主震和M_L≥3.0余震的震源位置，并利用较高精度的定位结果分析余震分布与地震构造的关系，解释发震断裂带的结构.获得的新认识有：（1）九寨沟主震震源深度为16 km，位于余震带中段的南缘；余震主要分布深度为4~17 km.（2）沿余震带的走向，余震分布与主震同震位错大小的分布明显相关.余震带中段8~16 km深度存在的余震稀疏区与同震位错的高值区相吻合，应是发震断裂带主凹凸体的部位，也是主震时应变释放较充分的部位；余震带南东段10~18 km深度的余震密集区对应了同震位错的亏损区之一，三次M_L≥5.0余震都发生于此；余震带西北段在5~10 km之下既缺少余震，又属同震位错的亏损区，可能与那里多条断裂的交汇或合并造成的构造复杂性有关；余震带中-北西段3~5 km深度的也缺少余震，也对应了浅部的同震位错亏损区.（3）证实了九寨沟地震的发震构造为虎牙断裂带北段，同时新揭示出发震断裂带表现为由主断裂和分支断裂构成的、向上分叉的花状结构，尺度约为4.5 km宽（最大）、35 km长，主断裂朝SW陡倾.这些反映主震破裂可能不只受控于单一的断裂，而有可能是沿主断裂发生主破裂，而沿分支断裂发生次要破裂.另外，本文对发震断裂带结构的分段解释，是遵循构造地质学原理去综合震源排列、震源机制解、地表断层已知位置、相邻剖面断层解释结果等信息的分析结果，而不仅仅依据余震的密集分布进行推断.
关键词: 九寨沟地震/
初至P震相/
重新定位/
震源深度/
发震构造

Abstract:Based on records of regional and mobile seismic stations (near the studied epicentral area),we have relocated the M_S7.0 mainshock and M_L ≥ 3.0 aftershocks in the 2017 Jiuzhaigou,Sichuan,earthquake sequence by using first arriving P-phase only. Then,we analyzed the relationship between aftershocks distribution and seismotectonic structure by using the high-precision relocation result,and further interpret the structure of seismogenic fault zone. Our study has yielded some new conclusions:(1) The Jiuzhaigou mainshock is now relocated near the southern end of the middle segment of the aftershock zone,with a focal depth of 16 km; most of the aftershocks are relocated at depths of 4 to 17 km. (2) Along the aftershock zone,the distribution density of aftershocks is obviously related to the size of co-seismic slip of the mainshock. On the middle segment of the aftershock zone,an area with sparse aftershocks at depths of 8 to 16 km coincides with the location with relatively large co-seismic slip,and therefore it is inferred as the position of the main asperity of the seismogenic fault zone or as the place where the strain released thoroughly during the mainshock. On the southeastern segment of the aftershock zone,an area with dense aftershocks exists at depths of 10 to 18 km,where all the three M_L ≥ 5.0 aftershocks occurred,and coincides with one of the areas of co-seismic slip deficit. On the northwestern segment of the aftershock zone,an area at the depth range below 5 to 10 km is not only one place lacking aftershocks but also one of the areas of co-seismic slip deficit,and this situation would be related to the structural complexity due to the intersecting or merging of several faults there. On the middle and northwestern segments of the aftershock zone,no aftershocks occurred at the depth between 3 and 5 km,which coincides with a shallow area of co-seismic slip deficit. (3) It is confirmed in this study that the seismogenic structure of the Jiuzhaigou earthquake is the northern segment of the Huya fault zone. At the same time,it is newly revealed that the seismogenic fault zone has an upward-splay flower-like structure composed of the main fault and several branch faults,with a scale of~4.5 km (at the largest) in width and~35 km in length,and with the main fault dipping steeply toward SW. These reflect that the mainshock rupture may not only be controlled by a single fault,but probably the main rupture occurred along the main fault and the secondary ruptures along several branch faults. In addition,in this study the interpretation of seismogenic faults for every segment is the result using the basic principle of structural geology to analyze hypocentral alignment,focal mechanism solutions,positions of surface faults and interpretations for adjacent segments,rather than inferring only from dense distribution of aftershocks.
Key words:Jiuzhaigou earthquake/
First arriving P-phase/
Relocation/
Focal depth/
Seismogenic structure



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