Tectono-Hydrology Research Group
To improve short- and intermediate-term forecasting of Nankai megathrust earthquakes, we conduct observations and analyses of groundwater and crustal deformation. Since 2000, it has become clear that, in the deeper extension of the presumed source region of Nankai megathrust earthquakes, phenomena such as deep low-frequency tremors—which have lower frequencies than ordinary earthquakes—and deep slow slip events that continue for several days, have repeatedly occurred. These findings suggest that such phenomena may contribute to short- and intermediate-term forecasting of great Nankai Trough earthquakes. Since 2006, AIST has established 20 new observation sites (shown as red circles in the figure) around the presumed source region of Nankai Trough earthquakes, where we have conducted not only groundwater observations but also measurements of crustal deformation (such as crustal strain) and seismic activity. In addition, we exchange observation data in real time with the National Research Institute for Earth Science and Disaster Resilience (NIED) and the Japan Meteorological Agency (JMA), and provide analysis results to the JMA. To enable rapid and detailed analysis of deep slow slip events and deep low-frequency tremors, both of which are essential for improving the forecasting accuracy of Nankai megathrust earthquakes, we are engaged in research to develop new observation and analysis methods.
Anticipated focal zone of the largest Nankai megathrust earthquake and observation sites established by AIST for earthquake forecasting, along with existing observation sites.
Member
- Yuichi Kitagawa (Leader, Group)
- Satoshi Itaba (Senior Researcher)
- Tadafumi Ochi (Senior Researcher)
- Suguru Yabe (Senior Researcher)
- Kohei Shimotsuma (Research Assistant)
- Norio Matsumoto (Technical Staff)
- Ayako Takahashi (Technical Staff)
- Tsutomu Sato (Senior Researcher) (concurrent)
I research the mechanism of groundwater changes associated with earthquakes. I have improved and validated the poroelastic theory using the observation data of groundwater responses to earthquake and crustal deformation. Recently, I contributed to construction of the AIST observatories in and around the Tokai, Kii peninsula, and Shikoku regions along the Nankai Trough and have been detecting short-term slow slip events using the observation data of groundwater and crustal deformation for monitoring of slips on the plate boundary.
For the purpose of forecasting the Nankai megathrust earthquake , I am currently studying slow slip events on the plate boundary. For high-precision monitoring of the slow slip events, I am developing analysis methods of geodetic data and technique of high-sensitivity borehole strain observation.
Monitoring crustal deformation in southwestern Japan(SWJ) by various types of geodetic data, and modeling temporal changes of interplate coupling and slow slip on the plate interface. At this point, I mainly analyzed daily GNSS data and inferred spatial distribution and variation of the coupling and the slow slip along Suruga-Nankai trough. Now I'm trying to reveal the whole picture of interplate coupling and slow slip in SWJ analyzing the old geodetic data such as leveling and tidal data.
I have studied tectonic tremor activities (seismic signals of "Slow Earthquake") in Nankai trough with seismic data (Hi-net, F-net, DONET, etc.). I want to understand the source physics of slow earthquake through revealing patio-temporal variations of tectonic tremor activities.
I have conducted development of time series analysis for groundwater data, estimation of groundwater-level anomalies associated with hypothetical preslip prior to the anticipated Tokai earthquake and in-situ calibration method of borehole strainmeter. I will perform time series analysis of borehole strain/tilt data and development of analysis methods for short-term slow slip events to contribute the forecast of the Nankai megathrust earthquake.