摘要:
安第斯山位于纳兹卡洋壳板块和南美板块之间,是全球地震频发区域之一,被誉为地震与活动构造学家的天然实验室。本文利用矿山探矿钻孔,采用水压致裂原位地应力测试技术,首次获取安第斯山中段千米深孔原地应力大小及方向随深度变化规律。结果表明测试深度范围内主应力的量值随深度增加而增大,水平最大、最小主应力及垂向应力量值范围分别为12.38~34.47 MPa,7.97~24.15 MPa和6.81~26.10 MPa,主应力之间的关系为σH>σv≥σh,σH/σh比值介于1.43~1.66之间。最大水平主应力方向与震源机制解和地表调查结果基本吻合。以实测地应力资料为基础,利用安德森断层理论及库伦摩擦破裂准则,探讨了震源深度(假定30 km)处的应力状态及断层达到临界破坏时的孔隙压力,结果表明除纳兹卡板块持续俯冲外,高孔隙压力可能是该区地震频发的主要原因。研究结果不仅为该区地震机理研究提供了实测资料,而且对世界应力图数据库具有重要补充价值。
关键词:
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安第斯山
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地应力
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地震
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高孔隙压力
Abstract:
Located between the Nazca oceanic plate and the South American plate, Andes is one of the seismic extremely active areas in the world and is also known as the natural laboratory among seismologists and geologists. In this paper, the magnitude and orientation of in situ stress and its variation with depth were obtained for the first time by using the kilometer depth prospect borehole in the central section of Andes and the hydraulic fracturing in situ stress measurement method. The results show that the magnitude of in situ stress increases with increasing depth. The ranges of maximum horizontal principal stress, minimum horizontal principal stress and vertical stress are 12.38~34.47 MPa, 7.97~24.15 MPa and 6.81~26.10 MPa respectively. The relationships of three principal stresses are σH>σv≥σh, and the ratios of maximum horizontal principal stress to minimum horizontal principal stress are in the range of 1.43-1.66. The orientation of maximum horizontal principal stress is almost consistent with the focal mechanism solution and surface survey results. Based on the in situ stress measurement results, this paper deals with the in situ stress state and critical pore pressure of assumed epicenter depth (30 km) on the basis of Anderson fault theory and Coulomb friction criteria. The results show that high pore pressure might have been the major factor responsible for the frequent earthquakes in this area besides the continued subduction of Nazca oceanic plate. The results achieved by the authors not only provide the in situ stress measurements for the seismic mechanism, but also serve as important supplements to the World Stress Map database.
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