2006 Fiscal Year Final Research Report Summary
Generation processes for large earthquakes and tsunami earthquakes off Sanriku estimated from the analyses of small repeating earthquakes
| Project/Area Number |
15510145
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Natural disaster science
|
|---|
| Research Institution | Tohoku University (2004-2006)
The University of Tokyo (2003) |
|---|
Principal Investigator |
MATSUZAWA Toru Tohoku University, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (20190449)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
OKADA Tomomi Tohoku University, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (30281968)
|
|---|
| Project Period (FY) |
2003 – 2006
|
| Keywords | repeating earthquake / similar earthquake / quasi-static slip / afterslip / characteristic earthquake |
|---|
| Research Abstract |
In order to fulfill a reliable earthquake prediction, we need to reveal the earthquake generation processes in detail. This study has been carried out to investigate the generation processes of large earthquakes and tsunami earthquakes using small repeating earthquakes. The characteristics of the plate boundary off Sanriku revealed by this study are as follows :
1. On the boundary, there are asperities (where seismic slip is dominant) surrounded by aseismic-slip regions.
2. Earthquakes with almost constant sizes have repeatedly occurred with almost constant time intervals on isolated asperities.
3. Even on the isolated asperities, earthquakes with non-similar waveforms (especially in the high-frequency components) can occur when aseismic slip in the surrounding region is fluctuated considerably.
4. In the regions where many small asperities are distributed, earthquake swarms and/or aftershock area expansion can occur because of the interaction between the seismic slip at the asperities and aseismic slip in the surrounding regions.
5. If asperities are located closely, several types of earthquakes can occur: some destroy all the asperities, some destroy only part of them. In this case, the earthquake repeating cycle becomes complicated.
6. Medium size earthquakes and their afterslip can promote nearby large earthquakes.
7. Pore pressure on the plate boundary is estimated to be very high and the effective normal stress is probably as low as 1/10 of lithostatic pressure.
8. Small repeating earthquake activity is very high just to the west of the source area of the 1896 Sanriku Tsunami earthquake, indicating there are many small asperities surrounded by aseismic regions. Moreover, low-frequency earthquakes are frequently observed there. These results are consistent with the model for the tsunami earthquakes proposed by Seno (2002).
|
