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3D mopping of the active-source fault systems in Japanese islands

日本岛屿活源断层系统的 3D 清理

基本信息

批准号：
14209004
负责人：
SATO Hiroshi
金额：
$ 30.87万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14209004/
关键词：
active fault seismogenic source fault Seismic profiling Japanese islands Balanced cross section Inversion Tectonics Crustal earthquake 活褶曲構造線 weak-fault tectonics 断層の深部形状活断層-震源断層システム地質構造発達史変動地形

项目摘要

The geometry of source fault, which generate devastative crustal earthquakes, is crucial for seismic hazard mitigation and evaluating the risk of active faults. In order to reveal the relationship between an active fault and a source fault, including their connectivity, seismic reflection profiles, surface geofogy and drill hole data were examined. In 2002, as an add on project to the deep seismic experiments across the SW Japan, we deployed 800 Texan recorders across the Shikoku island and recorded the explosive seismic signals by very dense interval (ca.120 m). The low-fold seismic sections portray the subducting slab and detailed crustal structure. The deeper extension of the Median Tectonic line is clearly traced by northward dipping reflections at 30 degrees. The oblique slip on the gently dipping fault plane is the dominant movements of the MTL.The geometry of the deeper extension of the Itoigawa-Shizuoka tectonic line(ISTL) active fault system, was also examined by seismic refle … More ction profiles and surface geology across the northern part of this fault system. The deep seismic reflection profiles suggests the low-angle geometry of the fault. Using the balanced cross section, kinematic basin evolution model has been examined. Based on this model, the northern part of the ISTL was a basin bounding normal fault and reactivated as a thrust, since the Pliocene.In 2003, the seismic reflection profiling was performed across the epicentral area of the 2003 Northern Miyagi earthquake (Mj 6.4) to correlate the geologic structure with seismic source fault. Seismic reflection profile indicated the reactivation of Miocene normal fault as reverse fault. The fault system corresponds to the eastern margin of the back-arc rift system. The deep geometry of source fault estimated from the distribution of aftershocks shows good agreement with the geometry estimated by balanced cross-section, indicating a whole upper crustal inversion of Miocene normal fault as a reverse fault.In 2004, similar rift system and basin inversion processes were examined along the Kitakami river valley, using the industry seismic reflection data and data of surface geology and microseismicity. According to the observation of microseismicity in the epicentral area of the 1962 Northern Miyagi earthquake. The array of hypocenters shows the west dipping, Istric geometry and accords well to the geometry of source fault of the 2003 earthquake. In Mizusawa area, a series of west dipping Miocene normal faults are well imaged by seismic reflection profiling. The active faults, such as the Dedana fault, are clearly demonstrated that they were produced by basin inversion processes. In case of such active faults, the dip angle of source fault is higher (ca.50℃) than that of simple reverse fault (ca.30℃).Though this research, it is well understood that in the crustal deformation processes, reactivation of pre-existing faults is very common. Thus, simple geophysical estimation based on rock mechanics, is not effective. Because the fault itself is produced in geological time when the stress condition was not same as in late Quaternary. Thus, the reconstruction of geologic processes using the balanced geologic cross sections, is very effective to estimate the deep geometry of the active fault system (source fault). Less

产生破坏性地壳地震的震源断层的几何形状对于减轻地震灾害和评估活动断层的危险性至关重要。为了揭示活动断层和源断层之间的关系，包括它们之间的连通性，研究了地震反射剖面、地表地质学和钻孔数据。2002年，作为日本西南部深部地震实验的补充项目，我们在四国岛部署了800台德克萨斯记录仪，以非常密集的间隔(约120米)记录了爆炸地震信号。低褶皱地震剖面描绘了俯冲板块和详细的地壳结构。中值构造线的更深延伸被30度向北的倾斜反射清楚地追踪出来。缓倾断层面上的斜滑是山体的主要运动形式。用地震反射…研究了岩川-静冈活动断裂系统的深部伸展几何学更多横跨该断裂系统北部的剖面和地表地质。深地震反射剖面显示了断层的低角度几何形状。利用平衡剖面，对盆地运动演化模型进行了检验。在此模型的基础上，ISTL北部为上新世以来以正断层为界、以逆冲断层为界的盆地。2003年，对2003年宫城北部6.4级地震震中地区进行了地震反射剖面图，将地质构造与震源断层进行对比。地震反射剖面显示中新世正断层为逆断层。断裂系统对应于弧后裂谷系统的东缘。根据余震分布估计的震源断层的深部几何形状与平衡剖面估计的几何形状吻合较好，表明中新世正断层是一个整体的上地壳反转断层。2004年，利用工业地震反射资料和地表地质和微震活动数据，在北上上河流域考察了类似的裂谷系统和盆地反转过程。根据1962年宫城北部地震震中微震活动的观测。震中排列呈西倾、ISTREC几何特征，与2003年地震的震源断层几何特征吻合较好。在水泽地区，地震反射剖面对一系列西倾中新世正断层进行了较好的成像。活动断裂，如德达纳断裂，清楚地表明它们是由盆地反转过程产生的。在这种活动断裂的情况下，源断裂的倾角(约50℃)大于简单逆断裂的倾角(约30℃)。通过本研究，可以很好地认识到，在地壳变形过程中，原有断裂的重新激活是非常常见的。因此，基于岩石力学的简单地球物理估算是不有效的。这是因为断裂本身是在地质时代产生的，当时的应力条件与晚第四纪不同。因此，利用平衡地质剖面重建地质过程，是估算活动断裂系统(源断层)深部几何形态的有效方法。较少