17:15 〜 19:15
[SSS07-P07] Characteristics of Focal Mechanism and Stress Field in The Eastern Boundary of the Sichuan-Yunnan Block
キーワード：earthquake focal mechanism, stress field inversion, principal stresses, the Eastern Boundary of the Sichuan-Yunnan Block
In this paper, we determined focal mechanism solutions of 3951 earthquakes of magnitude ML≧1.5 in the Eastern Boundary of the Sichuan-Yunnan Block and its adjacent from January 2008 to October 2020 by using broadband waveforms recorded by 128 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in the Eastern Boundary of the Sichuan-Yunnan Block, the earthquake mechanisms invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme. Results of the stress field inversion confirmed main active fault in the Eastern Boundary of the Sichuan-Yunnan Block is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in NW-SE and NWW-SEE direction, and they experience a clockwise rotation from north to south. Against the strike–slip background, normal faulting stress regimes and reverse faulting stress can be seen in the regional areas.
The shape ratio R-value varies significantly, the R- value in Sanchakou area is relatively high, with obvious extrusion characteristics, the R-values of Xianshuihe fault zone, Anninghe fault zone and Xiaojiang fault zone are all between 0.25-0.5, showing NE-SW compression and NW-SE tension, and the tensile stress may be much less than the compressive stress (strike slip type). The R values of the northern segment of Daliangshan fault zone, the southern segment of Anninghe fault zone and Zemuhe fault zone are all between 0.5-1, showing NW-SE compression and NE-SW tension, and the compressive stress is greater than the tensile stress. To sum up, the current stress characteristics of the eastern boundary of Sichuan Yunnan rhombic block are shear strain and local compression or tension.
The shape ratio R-value varies significantly, the R- value in Sanchakou area is relatively high, with obvious extrusion characteristics, the R-values of Xianshuihe fault zone, Anninghe fault zone and Xiaojiang fault zone are all between 0.25-0.5, showing NE-SW compression and NW-SE tension, and the tensile stress may be much less than the compressive stress (strike slip type). The R values of the northern segment of Daliangshan fault zone, the southern segment of Anninghe fault zone and Zemuhe fault zone are all between 0.5-1, showing NW-SE compression and NE-SW tension, and the compressive stress is greater than the tensile stress. To sum up, the current stress characteristics of the eastern boundary of Sichuan Yunnan rhombic block are shear strain and local compression or tension.