2003 Fiscal Year Final Research Report Summary
Do the gravity and geoid height changes accumulate during the course of earthquake cycle?
| Project/Area Number |
13440130
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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 | The University of Tokyo |
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Principal Investigator |
OKUBO Shuhei The University of Tokyo, Earthquake Research Institute, Professor, 地震研究所, 教授 (30152078)
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| Co-Investigator(Kenkyū-buntansha) |
SUN Wenke The University of Tokyo, Earthquake Research Institute, Associate Professor, 地震研究所, 助教授 (10323651)
FURUYA Masato The University of Tokyo, Earthquake Research Institute, Research Associate, 地震研究所, 助手 (60313045)
HIBIYA Toshiyuki The University of Tokyo, Graduate School of Science, Professor, 大学院・理学系研究科, 教授 (80192714)
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| Project Period (FY) |
2001 – 2003
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| Keywords | Viscoelasticity / Gravity / Fault motion / Active faults |
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| Research Abstract |
We formulated the gravity, geoid height and elevation changes due to fault motoin in a Maxwell viscoelastic earth. The formulation is implemented to a FORTRAN computer code, which enables us to compute interseismic gravity/elevation changes during an earthquake cycle based on the Savage's backslip model. We applied the technique to the interseismic deformation around the Tokai area where the Philippine Sea plate is subducting beneath the Eurasian plate.
The model successfully reproduces the steady subsidence when we assume reasonable viscosity profile and asperity distribution. On the contrary, we find the computed gravity change rate is significantly larger than the observed one. The result casts profound doubt on the validity of the Savage's supposition that no deformation accumulates over repeated seismic cycles.
We applied the formulation to the analysis of gravity change before and after the Tokachi-oki Earthquake (M8.1, September 26, 2003). To be more specific, we calculated the interseismic gravity change rate to reduce the absolute gravity value taken several years before the earthquake to the one just before the earthquake. When compared with the absolute gravity value just after the earthquake, it enables us to estimate the coseismic gravity change. The change agrees well with the theoretically predicted one.
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