形成新生断裂的临界角度及其与强烈地震发生的关系

选取具有薄弱面或破裂面的细粒花岗岩块状露头标本,在实验室模拟高温高压环境条件进行测试,研究岩石产生新破裂面的受力临界角度。在温度100℃、围压100 MPa和温度200℃、围压200 MPa的环境条件下,按照与主应力夹角的不同度数变化分别进行实验。实验结果表明,当夹角α处于0°~30°时,岩石沿原破裂面稳滑;夹角α处于30°~60°时,以粘滑为主;夹角α处于60°~90°时,以新破裂面的产生为主;可能产生新破裂面的临界角度范围为50°~65°,当夹角α大于65°时,新破裂产生。对岩石出现的稳滑-粘滑-新破裂现象,通过分析切面所受应力(σ)与应变率(ε)的关系进行了解释。根据莫尔圆理论认为,复杂断裂背景下,岩石的受力角度对于新破裂面的产生将有着决定性作用,而作用力状态一定时,新破裂产生的临界角度60°是可能导致强烈地震发生的危险值。

The critical angle which enables the formation of a new fracture and its relation with strong earthquake

The fine grained massive granite outcrop samples with a weak or broken surface were selected, the force critical angle which led to the new rupture surface of the rock was studied under high temperature and high pressure simulated in the lab. Under the temperature 100 ℃, confining pressure 100 MPa and the temperature 200 ℃, confining pressure 200 MPa, the experiments were made separately through changing the angle with principal stress. The results showed that when the angle α was 0°~30°, the rock steadily slipped along the original rupture surface; when the angle α was 30°~60°, the fault was dominated by stick slip; when the angle α was 60°~90°, mainly led to the generation of the new rupture surface; the critical angle likely to generate a new rupture surface ranges between 50°~65°; the new rupture occurred when the angle α was greater than 65°. The phenomenon, which occurred on rocks, such as stable sliding, stick slip, and a new rupture surface generation, was explained by analyzing the relationship between the stress from different slices (σ) and strain rate (ε) . As is showed in Mohr′s circle theory, under the complex fracture background, the rock stress angle has dominant effect on the generation of the new fracture, and for a given action condition, the critical angle 60° led to the new fracture was possibly the dangerous value which could cause the strong earthquake.