Establishment of a zoning method for fault bedrocks based on the strain partitioning of multiple faults and seismic properties of fault rocks

东北-西南向，105公里长的奥哈拉-W湖。柳山断裂系统(OYFS)发育于中部地区西部。该断层系统由多条断层组成。沿OYFS存在山口-出云地震带。活动断裂的活动可能与盆地的形成机制有关，因为盆地位于断裂的弯曲部位。另一方面，本研究将受断层运动影响且邻近断层的基岩定义为“断层基岩”，为减轻内陆地震造成的基岩灾害提供基础数据，建立了断层基岩地震危险性区划方法。本研究选取OYFS作为个案研究，调查内容及结果如下。通过断层岩石和断裂过程带的显微观测，揭示了OYFS构造断裂的面上构造形态，分析了各构造断裂的应变分配。分别在实验室岩样和露头岩样上测量了断层岩层和过程带的速度Vp和Vs，得到了断层基岩的地震性质。将地震特征与断层岩石的微观观测相结合，建立了断层基岩的分类标准。在此基础上，编制了OYF沿线地区的断层岩分类图。结合区域地质信息、地球物理资料和成果(1)，重建了多断裂系统的三维形态。利用二维有限元方法，在重建的多断层系统模型上模拟断层运动，并对地震危险性进行评价。

NE-SW-trending, 105-km long Lake Ohara -W. Yauneyama fault system (OYFS) is developed in western Chugoku District. This fault system is composed of multiple faults. The Yamaguchi -Izumo seismic zone exists along the OYFS. The movement of active faults may be related to a formational mechanism of these basins, because the basins are located at bending parts of the faults. On the other hand, in this study, bedrocks which are affected by a fault movement and are in the vicinity of a fault are defined as "fault bedrock".In order to obtain a basic data for mitigating bedrock disaster caused by inland earthquakes, this study establishes a zoning method of seismic hazards for the fault bedrock. We select the OYFS as a case study, and the contents of the investigation and results are as follows.1. Configuration of in plane view of the constituent fault of the OYFS is revealed, and strain partitioning of each constituent fault is analyzed by a combination microscopic observations of fault rocks and fault process zones.2. Velocities, Vp and Vs, of the fault rock and the process zone are measured on rock samples in a laboratory and on outcrops in situ, respectively, and seismic properties of the fault bedrock are obtained. By combining the seismic property with the microscopic observation of the fault rock, a classification criterion of the fault bedrock is developed. Based on the classification criterion, a classification map of fault rocks is made up in the area along the OYFS.3. Three-dimensional configuration of the multiple fault system is reconstructed by the combination of regional geology information, geophysical data and the result (1).4. Using a two-dimensional finite element method, fault movement is simulated on the reconstructed model of the multiple fault system, and the seismic risk is evaluated.