The crustal structures of the central Longmenshan along and its margins as related to the seismotectonics of the 2008 Wenchuan Earthquake

• Published in: Science China. Earth sciences Vol. 57; no. 4; pp. 777 - 790
• Main Authors: Jia, ShiXu, Liu, BaoJin, Xu, ZhaoFan, Liu, Zhi, Feng, ShaoYing, Zhang, JianShi, Lin, JieYan, Tian, XiaoFeng, Liu, QiaoXia, Guo, WenBin
• Format: Journal Article
• Language: English
• Published: Heidelberg Science China Press 01.04.2014; Springer Nature B.V
• Subjects: Basements; Basins; Belts; Crusts; Earth and Environmental Science; Earth Sciences; Earthquakes; Faults; Lithosphere; Plate tectonics; Research Paper; Seismic activity; Seismic phenomena; Seismic waves; Seismology; Tectonics; Upwelling; Wave velocity; 中央; 区域构造应力场; 发震构造; 地壳结构; 大地震; 宽角反射; 折射; 汶川; 龙门山; China; Asia, Qinghai-Tibet Plateau; brittle-ductile transition; crustal structure; Wenchuan earthquake; deep seismic sounding; central Longmenshan; crustal uplift
• ISSN: 1674-7313; 1869-1897
• DOI: 10.1007/s11430-013-4744-9

In 2010, a 500-km-long wide-angle reflection/refraction seismic profile was completed, running northwest from the central Sichuan Basin. This profile orthogonally crosses the meizoseismal area of great Wenchuan earthquake of 12 May 2008, which occurred in the central part of the Longmenshan. The profile also passes through the northwestern Sichuan Plateau, along which a new deep seismic sounding observation system was set up that was much improved over previous datasets and enabled abundant observations to be recorded. Seismic wave phase records that reflect the structural characteristics of different tectonic blocks, especially the complicated phase features associated with the Wenchuan earthquake, were calculated and analyzed in detail. A 2D crustal P-wave velocity model for the orogenic belt in the central Longmenshan and its margins was determined, and crustal structure differences between the stable Sichuan Basin and the thickened northwestern Sichuan Plateau were char- acterized. Lithological variations within the upper and lower crust in the interior of the plateau, especially a great velocity de- crease and plastic rheological properties associated with strong lithologic weakening in lower crust, were detected. From west to east in the lower crust beneath the orogenic belt lying between the Sichuan Basin and the northwestern Sichuan Plateau, a giant shovel-like upwelling is observed that dips gently in the lower part and at higher angles in the upper part; this is inferred to be related to the fault systems in the central Longmenshan. An upwelling in the upper-middle crust along the eastern margin of the orogenic belt is associated with steeply dipping thrusts that strongly uplift the upper crust and crystalline basement be- neath a central fault system in the Longmenshan. The data, combined with an understanding of the regional tectonic stress field and previous geological results, enable a discussion of basin-and-range coupling, orogenic tectonics, the crustal fault system, and the seismogenic tectonic environment of the central Longmenshan along the eastern margin of the Qinghai-Tibet Plateau.