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根据人工地震、重力、地质、航磁、大地电磁测深、地震活动及地球化学资料,研究了1920年海原大地震与构造的关系。结果表明:海原断层实际是深度不超过10km的铲状逆掩推覆断层,而海原大震的震源深度为15-20km,因此,海原断层与该次大震的发生无关。海原大地震的发生既与延至软流层顶部的近NS向和近EW向的构造有关,也与软流层的物质活动有关。海原断层上的各种地震形变为地震诱发的产物。 相似文献
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昌马断裂带是是青藏高原北部一条活动强烈的左旋走滑断裂带。它表现为重力、航磁、地壳厚度的综合异常梯度带,属于断面陡、切割深的超岩石圈断裂。昌马断裂带由12条长4公里至18公里不等的不连续的主断层和4条次级断层组成,可划分为东、中、西三大段落。断裂的水平位移和滑动速率具有分段性,全新世以来,东、中、西三段的左旋水平滑动速率分别为4.1毫米/年,2.6毫米/年和1.5毫米/年。北东东、北北西和北西西三个方向断层的位移具有分级特征,不同级别的位移具有良好的同步性。全新世以来北东东、北北西和北西西三个方向断层的水平滑动速率分别为4.1毫米/年、3.8毫米/年和2.7毫米/年。白垩纪以来,昌马断裂呈天平式运动,显示了枢纽断裂运动特征,枢纽轴位于断裂中段。昌马地震震源破裂性质及其反映的震源应力场与地震破裂带的破裂性质及其反映的构造应力场不一致。昌马地震震源机制解反映了北北西~南南东挤压,作用应力近于水平的震源应力场;昌马地震破裂带的变形组合反映了东北~南西挤压的构造应力场。昌马地震破裂带长120公里,分为东部正走滑段、中部逆走滑段和西部尾端破裂段,显示了多个水平位移峰值。全新世以来,沿昌马断裂发生了6次强震事件,强震复发 相似文献
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Velocity dependence of strength and healing behaviour in simulated phyllosilicate-bearing fault gouge 总被引:2,自引:0,他引:2
Despite the fact that phyllosilicates are widespread in fault zones, little is known about the strength of phyllosilicate-bearing fault rocks under brittle–ductile transitional conditions. In this study, we explored the steady state strength and healing behaviour of a simulated phyllosilicate-bearing fault rock, i.e. muscovite plus halite and brine, at room temperature, normal stresses of 1–9 MPa, atmospheric fluid pressure and sliding velocities of 0.001–13 μm/s, using a rotary shear apparatus. While 100% halite and 100% muscovite samples exhibit rate-independent frictional/brittle behaviour, the strength of mixtures containing 10–50% muscovite is both normal stress and sliding velocity dependent. At low velocities (< 1 μm/s), strength increases with increasing velocity and normal stress, and a mylonitic foliation develops. This behaviour results from pressure solution in the halite grains, which accommodates frictional sliding on the phyllosilicate foliation. The pervasive muscovite foliation, which coats all halite grains, prevents significant healing. At high velocities (> 1 μm/s), velocity-weakening frictional behaviour occurs, along with the development of a structureless, intermixed, cataclastic microstructure. The steady state porosity of samples deformed in this regime increases with increasing sliding velocity. We propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution. Towards higher sliding velocities, dilatation increasingly dominates over pressure solution compaction, so that porosity increases and frictional strength decreases. During periods of zero slip, pressure solution compaction occurs, causing a significant strength increase on reshearing. Our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions, but can simply result from oscillating fault motion rates. Our healing data suggest that foliated, aseismically creeping fault segments will remain weak and aseismic, whereas segments that have slipped seismically will rapidly re-strengthen and remain in the unstable, velocity-weakening regime. 相似文献