Characterization of the Subsurface Fracture Network by Means of Crystal Fracture Mechanics and Crystal Stress Study

通过晶体断裂力学和晶体应力研究表征地下断裂网络

• 批准号: 05044197
• 负责人: TAKAHASHI Hideaki
• 金额: --
• 依托单位: Tohoku University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Overseas Scientific Survey.
• 财政年份: 1993
• 资助国家: 日本
• 起止时间: 1993 至 无数据
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-05044197/
• 关键词: Fracture; Fractal; Subsurface Fractures; Numerical Simulation; Crustal Stress; Permeability; Connectivity; Rock

The observed fractal nature of both fault length distributions and earthquake magnitude-frequency distribution suggests that there may be a relationship between the structure of active fault systems and the resulting seismicity. Here, we present the first experimental evidence for a correlation between the fractal dimension of fracture length distribution D and acoustic emission (AE) b-value based on a series of tensile fracture mechanics tests on crystalline rock, carried out in different environmental conditions, both air-dry and water-saturated at ambient temperature and pressure. The constant stress intensity, K_I, and quantitative analyses of the resulting fracture patterns were carried out on the same specimens. It is found that AE b-values, ranging from 1.0 to 2.3, correlate negatively with normalized stress intensity K_I/K_<IC>, where K_<IC> is the fracture toughness of the specimen. The fractal dimension of fracture length distribution D, ranges from 1.0 to 1.7. Fluid presence has a first-order influence on both the AE and structure produced in these experiments. For experiments at low stress intensity or high fluid content, the activation of the stress corrosion mechanism for K_I < K_<IC> leads to a greater relative proportion both of small cracks and of low amplitude acoustic emissions, reflected in higher values of D and b. The fractal dimension D is found to correlate positively with the AE b-value.

观察到的断层长度分布和地震震级频率分布的分形性质表明，活动断层系统的结构与由此产生的地震活动性之间可能存在关系。本文通过在不同环境条件下（空气干燥和环境温度和压力下的水饱和）对结晶岩进行的一系列拉伸断裂力学试验，首次提供了裂缝长度分布D分形维数与声发射（AE） b值相关的实验证据。在相同的试样上进行了恒定应力强度、K_I和所产生的断裂模式的定量分析。结果表明，AE b值在1.0 ~ 2.3范围内与归一化应力强度K_I/K_<IC>呈负相关，其中K_<IC>为试样的断裂韧性。断口长度分布D的分形维数为1.0 ~ 1.7。流体的存在对实验中产生的声发射和结构都有一级影响。在低应力强度或高流体含量条件下，当K_I < K_<IC>时，应力腐蚀机制的激活导致小裂纹和低振幅声发射的相对比例增大，这体现在更高的D和b值上。分形维数D与声发射b值呈正相关。