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| | Abstract | | Three-dimensional density structure at the western district of Wakayama Prefecture was determined using 3D gravimetric tomography technique, and the relation between this density structure and background seismic activity was studied. In gravimetic tomography, simulated annealing was applied as a optimization argorithm, and several supplementary argorithms were introduced in order to reduce the problems arising from nonuniqueness and instability of the solution, such as smoothness constraints with sensitivity control, ensemble analysis, and modeling of geologic and geophysical a priori information. This study revealed the close and characteristic relations between density structure and background seismic acitivity as follows. 1. The east-west trend is dominant in the shallow structure, while the northeast-southwest trend is dominant in the deep structure. 2. Most hypocenters are distributed within the limited zone with the particular density of 2.62-2.68g/cm3. 3. Seismicity extends to the greater depth at the axis of the anticline near the Ryoumon-Dake. |
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