CRUSTAL STRUCTURE FROM YUNXIAN-NINGLANG WIDE-ANGLE SEISMIC REFLECTION AND REFRACTION PROFILE IN NORTHWESTERN YUNNAN,CHINA |
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| Authors: | CHEN Si-wen WANG Bao-shan TIAN Xiao-feng WANG Fu-yun LIU Bao-feng LI Lu |
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| Affiliation: | 1. Key Laboratory of Seismic Observation and Geophysical Imaging, Institute of Geophysics, China Earthquake Administration, Beijing 100081, China;
2. Geophysical Exploration Center, China Earthquake Administration, Zhengzhou 450002, China |
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| Abstract: | The Red River Fault in western Yunnan is one of the longest strike-slip faults in China and has a high seismic potential. To investigate its complicated structure, a near-NS directed 300km long wide-angle reflection/refraction seismic profile was laid out from Yunxian to Ninglang, across the Red River Fault. The 2-D velocity structure model along the profile was obtained through 1-D and 2-D analysis and fitting the observed data with combination of first-arrival traveltime tomography and forward modeling. The results indicate:In the crust, the average P-wave velocity is 6.2~6.3km/s and basically shows a positive gradient structure, but there are some low velocity anomalies at different area in upper and lower crust. Regarding the crust boundary, a relative large lateral variation exists in the depth of Moho, which goes deeper from south to north, ranging from 45km to as deep as 54km; compared to other typical continental crust, the study area demonstrates a striking thickening. It should be mentioned that the crustal thickening is mainly observed in the lower crust, while the upper and middle crust possess nearly constant thickness. We observed strong seismic velocity contrast across the Red River Fault, which emphasizes the role of the fault as an important tectonic boundary between Yangtze paraplatform and Sanjiang geosynclinal system. Along the profile, the Moho depth has no remarkable variation when crossing the Red River Fault. Combining with other study results on nearby area, it proves that there is notable heterogeneity between different parts of the Red River Fault. |
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| Keywords: | western Yunnan two-dimensional crustal velocity structure wide-angle reflection/refraction Red River Fault |
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