Study On Deep Structure And Dynamic Pattern Of Seismic Gap In Longmen Mountain Fault Zone By Using Teleseismic Receiver Function

The collision between India and Eurasia plate Since the Cenozoic Era has created the magnificent Himalaya-Tibetan Plateau orogenic belt,and in the process of this massive Tectonic movement,forming The largest Plateau on earth--Tibetan Plateau.The Longmen fault zone is located in the southeastern margin of the Tibetan Plateau,In recent years,the seismic activity is relatively active in this zone,In particular,The occurrence of the Wenchuan and Lushan earthquake have made it a research hotspots in the academic circles at home and abroad.A seismic gap with a horizontal distance of 40 km exists between Wenchuan and Lushan earthquakes.Study on deep tectonic setting of media in the area near strong earthquakes and seismic gap may shade lights on the seismogenic environment in these area.Using teleseismic data from 15 temporary observation stations deployed by our research group and 21 stations deployed by the Scientific Exploration of Lushan earthquake team(China Earthquake Administration)and 21 permanent stations from Seismological Bureau of Sichuan Province,we apply the H-k stacking method to estimate the crustal thickness and average poisson's ratio beneath each station,then build the receiver function common conversion point(CCP)images and the S-wave velocity model below seismic stations obtained by linear inversion.Our results reveal sharp contrast of crustal structure between source area of large earthquakes and seismic gap:(1)the average poisson's ratio of the crust in the source region of Wenchuan earthquake is ~0.28,and ~0.29 in the source area of Lushanearthquake;the poisson's ratio in the seismic gap varies dramatically;(2)below the source area of the Wenchuan earthquake and the Lushanearthquake,Moho depth deepensgradually westward(this is consistent with many other results),the Moho depth jump from ~44km to ~59km and ~40km to ~50km in the west of Lushan and Wenchuan earthquakes,respectively;butthe crustal thicknessalong the cross-section passing the seismic gap is relatively flat;(3)the seismic gap is characterized as a Moho depression and a low velocity in upper crust.Integrated 1-D S wave velocity structure and results of H-k and CCP stacking indicate the fault on which the Wenchuan earthquake is located may cut through the entire crustand tilt westward;the Lushan earthquake may be caused by a low-velocity zone in middle crust to decouple the deformation between the upper and lower crust;and the seismic gap may be in the transition zone of the two regions controlled by the two seismogenic mechanisms of the two big earthquakes.