3-D Seismic velocity structure and stress regime under Japan Islands

日本列岛下的 3-D 地震速度结构和应力状态

基本信息

批准号：
11440134
负责人：
ZHAO Dapeng
金额：
$ 6.4万
依托单位：
Ehime University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2002
项目状态：
已结题

项目摘要

We have used seismic tomography to study the 3-D crust and mantle structure and seismotectonics of the Japan Islands. A close relationship between large crustal earthquakes and structural heterogeneities is revealed. Most of the large crustal earthquakes occurred in or around the areas of low velocity that represent weak sections of the seismogenic crust. In volcanic areas the crustal weakening is caused by active volcanoes and arc magma. In forearc areas fluids are suggested in the large earthquake source zones, which have contributed to the rupture nucleation. The fluids originate from the dehydration of the subducting Philippine Sea slab. These results indicate that large earthquakes do not strike anywhere, but only anomalous areas which can be detected with geophysical methods.A new approach was used to conduct global tomographic inversions to study the deep structure of subducting slabs and mantle plumes. Strong and wide fast anomalies are visible in the transition zone depths under subduction regions, which suggests that most of the slab materials are stagnant in the transition zone before finally collapsing down to the lower mantle. Plume- like slow anomalies are clearly visible under the major hotspot regions in most parts of the mantle, in particular, under Hawaii, Iceland, South Pacific and Africa. The slow anomalies under hotspots usually do not show a straight pillar shape, but exhibit winding images, suggesting that plumes are not fixed in the mantle but can be deflected by the mantle flow. As a consequence, hotspots are not really fixed but can wander on the surface.

我们已经使用地震层析成像来研究日本群岛的3-D外壳结构和地震托克尼学。揭示了大型地壳地震与结构异质性之间的密切关系。大多数大型地壳地震发生在低速区域内或周围，代表了地震构成地壳的弱部分。在火山区域，地壳减弱是由活跃的火山和弧岩浆引起的。在前臂区域，在大地震源区域中建议流体，这导致了破裂的成核。液体源于俯冲菲律宾海板的脱水。这些结果表明，大地震不会在任何地方袭击，而只有可以通过地球物理方法检测到的异常区域。一种新的方法用于进行全球层析成像倒置，以研究俯冲板和地幔羽的深层结构。在俯冲区域下的过渡区深度可见强大而宽的快速异常，这表明大多数平板材料在过渡区停滞不前，然后最终倒塌到下层。在大部分地幔的主要热点地区，尤其是夏威夷，冰岛，南太平洋和非洲的大部分地区，在主要的热点地区，羽状慢的异常都可以清晰可见。热点下的慢速异常通常不会显示出直的柱状形状，而是表现出缠绕的图像，这表明羽毛不是固定在地幔中，而是可以被地幔流动偏转。结果，热点不是真正固定的，而是可以在表面上徘徊。