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.
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
作者
曾宪伟
闻学泽
龙锋
ZENG XianWei;WEN XueZe;LONG Feng(Earthquake Agency of Ningxia Hui Autonomous Region,Yinchuan 750001,China;State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Agency,Beijing 100029,China;Earthquake Agency of Sichuan Province,Chengdu 610041,China)
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2019年第12期4604-4619,共16页
Chinese Journal of Geophysics
基金
地震科技星火计划项目（XH18053Y）
宁夏自然科学基金项目（NZ14228）
国家自然科学基金（41604015）联合资助
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
Jiuzhaigou earthquake
First arriving P-phase
Relocation
Focal depth
Seismogenic structure
