HR: 0830h
AN: S31F-0826    [PDF]
TI: Dense Earthquake Observation and Deep Seismic Reflection Survey in Hypocental Region of the 2000 Tottori-ken Seibu Earthquake in Japan.
AU: * Abe, S
EM: shintaro@criepi.denken.or.jp
AF: CRI of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba-ken, 270-1194 Japan
AU: Aoyagi, Y
EM: y-aoyagi@criepi.denken.or.jp
AF: CRI of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba-ken, 270-1194 Japan
AU: Miyakoshi, K
EM: miyakosi@criepi.denken.or.jp
AF: CRI of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba-ken, 270-1194 Japan
AU: Inoue, D
EM: daiei@criepi.denken.or.jp
AF: CRI of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba-ken, 270-1194 Japan
AB: The Tottori-ken Seibu earthquake of October 6, 2000 was a large earthquake exceeding Mj 7. However, active fault was not pointed out on the existing map in hypocental region of this earthquake. This fact is very important in order to argue about the validity of predicting the magnitude of great or large earthquakes generated in the target area based on the results of earth scientific investigation. We carried out dense earthquake observation in which we installed 44 points in order to grasp the detailed form of earthquake source fault. Furthermore, we carried out seismic reflection prospecting of 3 observation lines which cross the earthquake source fault of main shock. We clarify the relevance of earthquake source fault and lineament. We interpreted S-P interval of the seismic wave obtained by earthquake observation, and carried out velocity analysis using travel time seismic tomography method. Low velocity zone was detected in the depth of about 2 km of hypocental region as a result of the analysis. The low velocity zone is distributed on earthquake source fault presumed from aftershock distribution. Generally fall in seismic wave velocity is caused by fall of rigidity. That is, it is thought that the low velocity zone was formed from destruction of the crust by fault activity. In the place where lineament and an observation line cross, two faults have been recognized in seismic reflection prospecting line-B. These faults seem to converge toward the depths. This geological structure is called flower structure, and it is characteristic underground structure formed of accumulation of lateral displacement. In this area, we were also carrying out aerial photograph interpretation and trench excavation. As a result, the geological proof that the lineaments were formed of left-lateral fault was acquired. That is, both underground structures and deformations of surface have lateral fault features. Faults recognized by seismic reflection prospecting and region crushed by the faults are located in the upper part of earthquake source fault presumed from aftershock distribution. However, the scale is too large if this crushed region was formed only by fault activity of the 2000 Tottori-ken Seibu earthquake. That is, it suggests that earthquakes with the same mechanism as the 2000 Tottori-ken Seibu earthquake occurred in this area repeatedly in the past. We calculated crustal movement when main shock occurs. The calculation technique is the stress deformation analysis which used the finite element method. We give rupture propagation of earthquake source fault as forced displacement to the elastic model of crustal structure in hypocental region. We solved process in which earthquake source fault forms lineament, based on this examination.
UR: http://criepi.denken.or.jp
DE: 7200 SEISMOLOGY
DE: 7221 Paleoseismology
DE: 7230 Seismicity and seismotectonics
DE: 8010 Fractures and faults
DE: 8123 Dynamics, seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting