Present-day movement trends of the major tectonic faults in the Sichuan-Yunnan region based on the constraint of GPS velocity fields

摘要

Based on the known fault distribution in Sichuan-Yunnan region (SYR), a rigid Euler rotation model is constructed by using GPS velocities (1998～2016) after excluding the stations near the fault boundaries and simultaneously a translation-rotation-strain model is constructed by using almost all GPS velocities to calculate three periods strain rate fields (2008.6 ～ 2010.4, 2010.5 ～ 2013.4 and 2013.5 ～2016.12) after Wenchuan earthquake. The results show that: (1) the strike-slip activity is the most common trends for the regional faults. The Xianshuihe-Xiaojiang fault, the Lancangjiang-Weixi-Weishan-Wuliangshan fault and the Longmenshan fault are the most active in the whole SYR, and the dislocation rate is more than 15 mm/a, and the trend of activity gradually decreases from the northwest to the southeast. (2) The different activity rates of the faults in the study area indicate that some of the eastward extrusion of the Tibet Plateau is absorbed and adjusted by the inside faults, and it is not a few large strike-slip faults. (3) Through the analysis of three periods' grid velocity fields, we found that the movement rates of the Bitu section of Lanchangjiang fault, the Northwestern section of Weixi-Weishan fault and the Nujiang fault after Wenchuan earthquake are larger than that after Yushu and Ya'an earthquake, and the difference is about 8 mm/a. Besides, the activity rate of Northwestern section of Longmenshan fault after the Wenchuan earthquake is larger than that after the Ya'an earthquake, although the two epicentres distances are relatively close. (4) The strain rate fields and surface expansion rates show that the high value area is mainly distributed at or around the intersection among some fault zones and its surroundings, and the maximum area is mainly located at some long and deep fault zones such as the Longriba fault, the Longmenshan fault zone, the Ganzi-Yushu fault and the Xianshuihe, and the magnitude is about 35 ～ 50 nanstrain/a. The research should provide fundamental material for the study of crustal stress variation and earthquake prediction in Sichuan-Yunnan region.