摘要
2014年10月7日云南景谷地区发生MS6.6地震,震源机制显示此次地震为逆走滑型,地震断层面走向140°,同时余震分布显示破裂面走向也为NNW向。文中对1条横穿景谷震区,与地震破裂面垂直的大地电磁测线数据进行了由定性到定量的全面分析,通过二维非线性共轭梯度（NLCG）反演得到了震源区较为详细的地壳电性结构。结果表明：1）震源区电性结构可以分为4层：地表以下约4km为相对低阻层,主要由中、新生代盆地沉积岩组成,电阻率10~100Ω·m;地下5~10km为相对高阻层,可能由元古界变质岩系组成,电阻率〉1000Ω·m;15~30km为中下地壳低阻层,电阻率〈10Ω·m;30km以下为壳幔过渡层,电阻率值约为30Ω·m。2）景谷地震主震发生在高阻层和壳内低阻层的分界面上。3）对余震的震源深度统计发现5km和10km两个深度范围内余震较多,与电性梯度带的位置相对应。
The October 7,2014 MS6. 6 earthquake in southwest of Jinggu in the southwestern Yunnan Province occurred as the result of shallow strike-slip faulting within the crust of the Eurasia plate in the broad plate boundary region between the India and Eurasia plates. The strike of fault plane is140°,and the aftershock distribution shows that the rupture plane is also NNW-trending. Tectonics of the region are controlled by the convergence of the India plate with Eurasia,which has driven the uplift of the Himalayas to the west of this earthquake,and has caused the formation of numerous intraplate continental transform structures in the surrounding region. The pattern of elastic- wave radiation from the earthquake is consistent with the shock occurring either as the result of right-lateral faulting on a northwest-trending fault or as the result of left-lateral faulting on a northeast trending fault. Faults of both types have been mapped in southwestern Yunnan,and it is unclear at this time which type of fault hosted this event. Magnetotelluric survey line is across Jinggu earthquake zone. The advanced data processing and analysis technology of MT is employed and the quantitative data from field surveys are analyzed to acquire the reliable electrical model. The MT data are inverted using nonlinear conjugate gradient（ NLCG） inversion algorithm. At last,the interpretation of the electrical model is performed considering the geology and the other geophysical data. Based on the final inversion model of the target profile,it is found that：（ 1） Electrical structure of the source region can be divided into four layers： The surface is relatively low resistivity layer（ 0 ~ 5km）,consisting mainly of Mesozoic and Cenozoic Basin sedimentary rocks,the value of resistivity is 100Ω·m; The high resistivity layer（ 5 ~ 10km） in upper crust mainly consists of Proterozoic metamorphic rocks,with resistivity higher than 1000Ω·m; there are the upper crust high-conductivity layer（ 15 ~ 25km） and crust-mantle transition zone（ blow 25km）;（ 2） The focal depth of the Jinggu earthquake is about10 km,which locates in the interface between high resistivity layer and high-conductivity layer;（ 3）Most of the focal depths of the aftershocks are in the range of 5km and 10 km,and the two depths（ 5km 10km） are corresponding to the resistivity gradient belt.
出处
《地震地质》
EI
CSCD
北大核心
2016年第2期352-369,共18页
Seismology and Geology
基金
地震行业科研专项(20100800102)
地震动力学国家重点实验室自主课题(LE1203)共同资助
关键词
景谷地震
大地电磁测深
电性结构
电性梯度带
地震构造
Jinggu earthquake
magnetotelluric
electrical structure
resistivity gradient belt
seismotectonics
