关键词: 川滇地区 震源机制解 区域应力场 阻尼反演

Abstract: Based on the focal mechanism solutions of 2600 ML≥3.0 earthquakes in Sichuan and Yunnan area from January 2000 to March 2017, the focal mechanism quantitative classification and stress field inversion are carried out for the sub blocks and fault zones with relatively dense focal mechanisms. Using the focal mechanism solutions of 727 ML≥4.0 earthquakes from January 1970 to March 2017, the regional stress tensor damping method is used to inverse the spatial distribution of principal compressive stress in Sichuan and Yunnan area before and after Wenchuan Ms8.0 and Lushan Ms7.0 earthquakes, and the temporal and spatial evolution characteristics of current stress field are discussed. The focal mechanism is mainly strike slip type in Sichuan and Yunnan area, but there are local differences. The Longmenshan fault zone is dominated by thrust type earthquakes, while the Mabian-Yanjin fault zone has relatively more strike slip and thrust type earthquakes, The types of earthquakes in Sichuan Basin are complex, and there is no obvious dominant type.The stress field in Sichuan and Yunnan area has obvious subarea characteristics, and it rotates clockwise from north to south. The compressive stress in Longmenshan fault zone and Sichuan Basin shows nearly EW direction. It shows NWW direction in the eastern boundary of Sichuan and Yunnan rhombic block, the inner part of rhombic block shows NNW direction, while the western and Southern Yunnan blocks show NNE direction.The principal compressive stress in Sichuan is more complex than that in Yunnan. The principal compressive stress direction in Sichuan experiences EW-NW-EW rotation from west to East. The principal compressive stress direction in Yunnan is NNE in the west, NNW in the East, forming an inverted "V" shape in space. Before and after the Wenchuan MS8.0 and Lushan MS 7.0 strong earthquakes, the stress field in the Longmenshan fault zone changed greatly, followed by the Sichuan Basin and its surrounding areas, and there was no obvious change in other areas of Sichuan and Yunnan. The stress field in the Longmenshan fault zone experienced a complete transformation process from basic stress field to variable stress field to basic stress field.

Key words: Sichuan and Yunnan area, Focal mechanism solution, Regional tress field, Damped inversion