1998 Fiscal Year Final Research Report Summary
Research on earthquakes, crustal movements and groundwater discharge changes in the Rokko active fault region
| Project/Area Number |
08454123
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
固体地球物理学
|
|---|
| Research Institution | KYOTO UNIVERSITY |
|---|
Principal Investigator |
FUJIMORI Kunio Kyoto University, Graduate School of Science, Lecturer, 大学院・理学研究科, 講師 (00025470)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
OTSUKA Shigeaki Kobe Gakuin University, Faculty of Humanities and Sciences, Professor, 人文学部, 教授 (00122242)
HIGASHI Toshihiro Kyoto University, Graduate School of Science, Instructor, 大学院・理学研究科, 助手 (90135517)
TAKEMOTO Shuzo Kyoto University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (40027256)
|
|---|
| Project Period (FY) |
1996 – 1998
|
| Keywords | Hyogo-ken Nanbu Earthquake / earthquake / crustal deformation / active fault / postseismic deformation / groundwater discharge / pore pressure / earth tide |
|---|
| Research Abstract |
Continuous observations of crustal strains and tilts have been executed in the stations (Rokko-Takao, Rokko-Syakunage and Rokko-Turukabuto), which are located within the focal region of the 1995 Hyogo-ken Nanbu earthquake (M=7.2). The observation tunnels of the Rokko-Takao and Rokko-Tsurukabuto are crossing with the Manpukuji and Otsuki faults, respectively. In the Rokko-Takao, change in groundwater discharge from the fracture zone of the Manpukuji fault has beeu also measured. In this work, the observations were continued after the earthquake, and the data analysis was done.
At the Rokko-Tsurukabuto station, a maximum strain change of 400μ strain and a maximum height change of 8.7mm caused by the earthquake were observed. Short-term changes or changes immediately before the earthquake were not detected, but a slow decrease of strain rates, small rotations of the maximum strain directions and a relative upheaval of about 0.1mm/year continued for a long time prior to the earthquake. After the earthquake, the Otsuki fault started lateral and vertical dislocations of a rate of 0.1-0.2mm/year. The dislocations are the same sense as the Quaternary movements of the fault.
A post-seismic crustal deformation which has a comparatively long time constant might be observed after a step-like coseismic crustal deformation. As causes where such deformatian is caused, an after-slip in the vicinity of a hypocenter, and a visco-elastic response of the crust to coseismic slipping have been considered. In present research, we consider that the coseismic strain changes generate the coseismic pore pressure changes which corresponds to the strain changes and that the postseismic crustal deformation is caused by groundwater migrations from the high pressure areas to the low pressure areas including the ground surface. The migration rates might be controlled by permeability of those areas.
|
