Real-Time Observation of Faulting Process in Rock by Seismic Computer Tomography

利用地震层析成像技术（CT）观测了单轴压缩条件下膨胀性（微裂纹）破坏前的局部化过程。利用该技术，通过分析沿沿着多条地震射线路径的扫描走时，可以绘制出岩石样品某一切片平面内的纵波速度分布。由于地震波的传播速度受传播路径沿着微裂纹的密度、纵横比和体积的影响，因此这些图可能有助于了解断裂过程。地震CT被认为是一种有利的技术来观察岩石中的微裂纹的定位。在地震速度各向异性补偿和测量系统精度方面对地震CT进行了改进，最后将地震CT应用于断层前岩石渗透性的定位观测。地震CT可以绘制纵波速度的空间分布图。由于P波速度是由非线性的程度决定的，因此绘制地震剖面图对于非破坏性地观察非线性的逐渐发展是有用的。大岛花岗岩试件在单轴应力下以恒定变形速率压缩。在几个应力水平下，在垂直于载荷轴的平面内进行重建。另一方面，我们利用地震CT显示了水渗入干燥花岗岩的现象，并描述了它的存在。通过对地震剖面的重建，可以观察到水在相互连通的微裂隙中的传播行为。

The seismic computer tomography (CT) was applied to observe how dialatancy (microcrack) localizes before fauting under uniaxial compression. By this technique, the distribution of P-wave velocity within a some sliced plane of the rock specimen can be mapped by analyzing the scanned travel times along a number of seismic ray paths. Because the velocities of seismic waves are influenced by the density, aspect ratio, and volume of microcracks along the transmitted path, the maps may be useful to see the process of faulting.We applied seismic CT preliminarily to the specimen of Oshima granite, once uniaxially compressed to post-peak region and then recovered without crushing. The seismic CT was found to be a favorable technique to observe the localization of microcracks in rock. This seismic CT was improved with regard to the compensation for anisotropy of seismic velocity and the accuracy of measuring systems.Finally, the seismic CT was applied to observe how dilatancy of rock localizes before faulting. The seismic CT can map the spatial distribution of P-wave velocities. Since P-wave velocity is determined by the extent of dilatancy, mapping the seismic profile is useful for observing non-destructively the progressive development of dilatancy. The specimen of Oshima granite was compressed at a constant deformation rate under uniaxial stress. The reconstructions were made within the plane perpendicular to the loading axis at several stress levels. The obtained maps clearly show the metamorphic changes of dilatancy before faulting.On the other hand, we applied the seismic CT to visualize the water infiltration into dry granite and to characterize its presence. For the result, the behavior of water spreading through the interconnecting mecrocracks could be observed by reconstructing the seismic profiles.