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THE DEPTH OF MOHO INTERFACE AND CRUSTAL THICKNESS IN SICHUAN-YUNNAN REGION,CHINA

XU Zhi-ping;WANG Fu-yun;JIANG Lei;XU Shun-qiang;TANG Lin;Geophysical Exploration Center,China Earthquake Administration;Sichuan Earthquake Agency;  
By using moving average method to separate Bouguer gravity anomaly field in Sichuan-Yunnan region,we got the low-frequency Bouguer gravity anomaly field which reflects the undulating of Moho interface. The initial model is obtained after seismic model transformation and elevation correction.Then,we used Parker method to invert the low-frequency Bouguer gravity anomaly field to obtain the depth of Moho interface and crustal thickness in the area. The results show that the Qinghai-Tibet block in the northwest of the study area deepens and thickens from the edge to the interior,with the depth of Moho interface and the crust thickness of about 52 ~ 62 km and 54 ~ 66 km,respectively. The depth of Moho interface in Sichuan Basin is about 38 ~ 42 km. In Sichuan-Yunnan block,the depth of Moho interface is about 42 ~ 62 km from southeast to northwest. Beneath the West Yunnan block,west of the Red River fault zone,the Moho depth is about 34 ~ 52 km from south to north. The Longmen Mountains and Red River fault zone are the gradient zone of the Moho depth change. Along the Red River fault zone,the depth difference of Moho interface is increasing gradually from north to south. No obvious uplift is found on the Moho interface of Panzhihua rift valley. The depth of Moho interface distribution in Sichuan and Yunnan is obviously restricted by the collision between the Indian plate and the Eurasian plate and the lateral subduction of the Indo-China peninsula. The mean square error of the depth of Moho interface is less than 1. 7 km between the result of divisional density interface inversion and artificial seismic exploration. At the same time,we compared the integral with divisional inversion result. It shows that: in areas where there is obvious difference between the crust velocity and density structure in different tectonic blocks,the use of high resolution seismic exploration data as the constraints to the divisional density interface inversion can effectively improve the reliability of inversion results.
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