THE DISCUSSION FOR THE NEW ACTIVITY OF THE TIANQUAN SEGMENT OF LONGMENSHAN FAULT ZONE AND ITS RELATIONSHIP TO THE 1327 TIANQUAN EARTHQUAKE,SICHUAN |
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| Authors: | LIANG Ming-jian CHEN Li-chun RAN Yong-kang WANG Hu LI Dong-yu |
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| Institution: | 1.Institute of Geology, China Earthquake Administration, Beijing 100029, China;2.Earthquake Administration of Sichuan Province, Chengdu 610041, China |
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| Abstract: | The 2008 Wenchuan earthquake occurred along the Longmen Shan fault zone, only five years later, another M7 Lushan earthquake struck the southern segment where its seismic risk has been highly focused by multiple geoscientists since this event. Through geological investigations and paleoseismic trenching, we suggest that the segment along the Shuangshi-Dachuan Fault at south of the seismogenic structure of the Lushan earthquake is active during Holocene. Along the fault, some discontinuous fault trough valleys developed and the fault dislocated the late Quaternary strata as the trench exposed. Based on analysis of historical records of earthquakes, we suggest that the epicenter of the 1327 Tianquan earthquake should be located near Tianquan and associated with the Shuangshi-Dachuan Fault. Furthermore, we compared the ranges of felt earthquakes(the 2013 M7 Lushan earthquake and the 1970 MS6.2 Dayi earthquake)and suggest that the magnitude of the 1327 Tianquan earthquake is more possible between 6½ and 7. The southern segment of the Longmen Shan fault zone behaves as a thrust fault system consisting of several sub-paralleled faults and its deep structure shows multiple layers of decollement, which might disperse strain accumulation effectively and make the thrust system propagate forward into the foreland basin, creating a new decollement on a gypsum-salt bed. The soft bed is thick and does not facilitate to constrain fault deformation and accumulate strain, which produces a weak surface tectonic expression and seismic activity along the southern segment, this is quite different from that of the middle and northern segments of the Longmen Shan fault zone. |
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| Keywords: | the 1327 Tianquan earthquake historical earthquake the southern segment of the Longmen Shan fault zone the seismogenic structure Shuangshi-Dachuan Fault |
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