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Tomography of 3D P-wave Velocity Structure of Crust at Southeast Margin of Taihang Mountains Fault Zone

XIN Hai-liang;LIU Ming-jun;ZHANG Yuan-sheng;KANG Min;Geophysical Exploration Center,China Earthquake Administration;School of Earth and Space Sciences,University of Science and Technology of China;Lanzhou Institute of Seismology,China Earthquake Administration;  
We present a new three-dimensional model of the crustal P-wave velocity structure of the southeastern margin of the Taihang Mountains fault zone,which we developed by inverting 14 078arrival-time data recorded by a local seismic network from 1981 to 2012.The results provide important new insights into the deep structure environment of the research region.The tomographic images show that the velocity distribution can be used to describe the characteristics of the surface topography and geologic structure at shallow depths,while in the deeper crust,the velocity distribution exhibits obvious lateral variation characteristics.The results for depths of less than 12 km represent the northern study area where the Taihang Mountains crustal uplift is located,which is mainly characterized as a high-speed zone.However,the south-ern settlement area of the low-speed zone and the results for depths greater than 12 km exhibit reversed characteristics.The velocity sections reveal that the velocity anomaly is roughly in line with the direction of nearby active faults.Based on the velocity profile,we determined the crust in the study area to be layered such that it could be divided into three layers,with the upper crust having a depth of 10 km.With respect to the lateral velocity change,there is little variety in the upper crust,but great variety in the middle and lower crusts.Earthquakes are mainly distributed in the range of 4km to 20 km depth in the crust.On the basis of our analysis of the relationship between the velocity,faults,and strong earthquakes,we speculate that our study area has the necessary preparation conditions for the occurrence of a strong earthquake.
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