WANG XuBen,
ZHANG Gang,
ZHOU Jun et al
.2018.Crust and upper mantle electrical resistivity structure in the Longmenshan tectonic belt and its relationship with Wenchuan and Lushan earthquakes.Chinese Journal Of Geophysics,61(5): 1984-1995,doi: 10.6038/cjg2018M0233
Crust and upper mantle electrical resistivity structure in the Longmenshan tectonic belt and its relationship with Wenchuan and Lushan earthquakes
WANG XuBen1, ZHANG Gang2, ZHOU Jun3, LI DeWei1, LUO Wei1, HU YuanBang4, CAI XueLin4, GUO ZiMing1
1. Key Lab of Earth Exploration & Information Techniques of Ministry of Education, Chengdu University of Technology, Chengdu 610059, China;
2. School of Environment and Resource, Southwest University of Science and Technology, Sichuan Mianyang 621010, China;
3. University of Electric Science and Technology, Chengdu 610041, China;
4. College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China
Longmenshan tectonic belt, located at the eastern border of Qinghai-Tibet Plateau, is an important area for studying the eastward lateral extrusion of crustal matter in Qinghai-Tibet Plateau. In order to explore the active tectonic features of Longmenshan tectonic belt and its relation with seismogenic structure, we arrange a magnetotelluric sounding profile at the focal area of Lushan Earthquake in the southern section of the vertical Longmenshan tectonic belt, gains a reliable electric structure of the research area by using various data processing methods and makes a comparison of the sounding profile of the middle section and north section of Longmenshan. The research shows: (1) A clear low-resistivity abnormal zone exists in the eastern Qinghai-Tibet Plateau, which distribute along Longriba fault-Minshan fault-back range faults at longmenshan fault. This low-resistivity abnormal zone forms a deep dynamics mode which features the subduction of Songpan-Garzê block to Yangtze block. Through statistics analysis of strong earthquakes in the research area in history, it is found that the earthquake focus is mainly distributed along eastern of the low-resistivity zone. Meanwhile, low-resistivity abnormal zone is also a low-seismic velocity and low-density abnormal zone. The lithosphere at the western border of Yangtze Block is bounded by the low-resistivity abnormal zone; (2) During the eastward movement of substances in the Qinghai-Tibet Plateau, the mantle rock and substances, blocked by the Sichuan Basin, get obducted and thrusted. The thin-skinned structure, featuring over-thrust, and substances from the middle-lower crust and the top of the upper mantle subduction deeply to the lithosphere of the Longmenshan tectonic belt. At the later stage of the Indosinian movement, Yangtze ancient block continues to subduct to the Northern China block, and, under the impact of the above-mentioned structure movement, forms wedge structure brought about by the westward breaking of high-resistivity wedge in the western border of rigid upper Yangtze block into the soft Qinghai-Tibet Plateau block; (3) According to the electrical resistivity structure, the affect of expansion of concealed crust-mantle ductile shear zone in the deep part may be one of the major power sources in the deep part of Lushan earthquake. The occurrence of Wenchuan earthquake, caused a stress loading area in south of Longmenshan structure zone, is another power source to trigger or accelerate the Lushan earthquake gestation and occurrence after a certain time of energy accumulation and stress transfer.
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