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2008年5月12日在中国四川省西部汶川发生Ms8.0地震,震中位于青藏东缘龙门山断裂带。地震发生后的4个月,沿龙门山断裂带中南段开展了原地应力测量,获得了3个测点的应力大小和方向。在3个测孔中浅部采用压磁应力解除法,深部采用水压致裂法。浅部测量结果显示,位于震中区映秀测点,水平最大主应力值为4.3MPa,最大主应力方向为N19°E;宝兴测点位于震中区西南的龙门山断裂带南段,汶川地震没有导致该段地表破裂,该点获得的水平最大主应力值为9.8MPa,最大主应力方向为N51°W;位于龙门山断裂带最西南端的康定测点,水平最大主应力值为2.6MPa,最大主应力方向为N39°E。利用水压致裂法对各钻孔100～400m深度进行了应力测量,获得了应力随深度变化趋势和应力状态。与震前其它应力测量结果和中国其它地区表层地应力测量结果比较,龙门山断裂带西南段处于相对高应力水平,震中区仍处于中等应力水平。这项研究成果将为评价龙门山断裂带余震和今后强震发展趋势提供关键构造物理参数。
On May 12, 2008, an Ms 8.0 earthquake occurred in Wenchuan, western Sichuan Province of China, and the epicenter was located in the Longmen Shan fault zone on the eastern edge of Qinghai-Tibet Plateau. Four months after the earthquake, in-situ stress measurements were carried out along the central-southern Longmenshan fault zone, and the stress magnitude and direction of the three measuring points were obtained. In the three holes in the shallow pressure magnetic stress relief method, deep hydraulic fracturing method. The shallow measurements show that the maximum horizontal principal stress is 4.3 MPa and the direction of the maximum principal stress is N19 ° E at the Yingxiu measuring point in the epicenter area. The Baoxing measuring point is located in the south segment of the Longmenshan fault southwest of the epicenter area without Wenchuan earthquake Resulting in the surface rupture. The maximum principal stress value at this point is 9.8 MPa and the maximum principal stress direction is N51 ° W. The maximum principal stress value at Kangding measuring point located at the most southwestern end of the Longmenshan fault zone is 2.6 MPa, the maximum The principal stress direction is N39 ° E. The hydraulic fracturing method was used to measure the depth of each drilling hole from 100m to 400m. The stress variation with depth and the stress state were obtained. Compared with the results of other stress measurements before the earthquake and the surface stress measurements of other parts of China, the southwestern segment of the Longmenshan fault zone is at a relatively high level of stress and the epicentral region is still at a moderate level of stress. The results of this study will provide key tectonic parameters for evaluating the aftershocks of the Longmenshan fault zone and the trend of future strong earthquakes.