GPS-constrained inversion of present-day slip rates along major faults of the Sichuan-Yunnan region, China

Abstract

A linked-fault-element model is employed to invert for contemporary slip rates along major active faults in the Sichuan-Yunnan region (96°–108°E, 21°–35°N) using the least squares method. The model is based on known fault geometry, and constrained by a GPS-derived horizontal velocity field. Our results support a model attributing the eastward extrusion of the Tibetan Plateau driven mainly by the north-northeastward indentation of the Indian plate into Tibet and the gravitational collapse of the plateau. Resisted by a relatively stable south China block, materials of the Sichuan-Yunnan region rotate clockwise around the eastern Himalayan tectonic syntaxis. During the process the Garze-Yushu, Xianshuihe, Anninghe, Zemuhe, Daliangshan, and Xiaojiang faults, the southwest extension of the Xiaojiang fault, and the Daluo-Jinghong and Mae Chan faults constitute the northeast and east boundaries of the eastward extrusion, with their left slip rates being 0.3–14.7, 8.9–17.1, 5.1 ± 2.5, 2.8 ± 2.3, 7.1 ± 2.1, 9.4 ± 1.2, 10.1 ± 2.0, 7.3 ± 2.6, and 4.9 ± 3.0 mm/a respectively. The southwestern boundary consists of a widely distributed dextral transpressional zone other than a single fault. Right slip rates of 4.2 ± 1.3, 4.3 ± 1.1, and 8.5 ± 1.7 mm/a are detected across the Nanhua-Chuxiong-Jianshui, Wuliangshan, and Longling-Lancang faults. Crustal deformation across the Longmenshan fault is weak, with shortening rates of 1.4 ± 1.0 and 1.6 ± 1.3 mm/a across the Baoxing-Beichuan and Beichuan-Qingchuan segments. Northwest of the Longmenshan fault lies an active deformation zone (the Longriba fault) with 5.1±1.2 mm/a right slip across. Relatively large slip rates are detected across a few faults within the Sichuan-Yunnan block: 4.4±1.3 mm/a left slip and 2.7±1.1 mm/a shortening across the Litang fault, and 2.7±2.3 mm/a right-lateral shearing and 6.7±2.3 mm/a shortening across the Yunongxi fault and its surrounding regions. In conclusion, we find that the Sichuan-Yunnan region is divided into more than a dozen active micro-blocks by a large number of faults with relatively slow slip rates. The eastward extrusion of the Tibetan Plateau is absorbed and adjusted in the region mainly by these faults, other than a small number of large strike-slip faults with fast slip rates.