| Project/Area Number |
11440134
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体地球物理学
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| Research Institution | Ehime University |
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Principal Investigator |
ZHAO Dapeng Ehime University, Geodynamics Research Center, Professor, 地球深部ダイナミクス研究センター, 教授 (70304665)
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| Project Period (FY) |
1999 – 2002
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| Project Status |
Completed (Fiscal Year 2002)
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| Budget Amount *help |
¥10,000,000 (Direct Cost: ¥10,000,000)
Fiscal Year 2002: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2001: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2000: ¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 1999: ¥5,000,000 (Direct Cost: ¥5,000,000)
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| Keywords | Seismology / Seismic tomography / Earth's interior Structure / hotspot / mantle plume / subduction zone / volcanoes / fluids / マントルプルーム / 深発地震 / トモグラフィー / 地殻大地震 / クラック密度 / 活火山 / 活断層 / 兵庫県南部地震 / 地震構造 / 直下型地震 |
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| Research Abstract |
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.
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