10:45 AM - 12:15 PM
[SGD02-P11] Temporal Change of the Crustal Deformation Rate in the Tokai Region, Central Japan, over the Last 40 Years
The Tokai region in central Japan has been subjected to many large earthquakes due to interplate coupling. In order to monitor the crustal deformation in the interseismic period, many kinds of geodetic observations have been conducted. I summarize the spatiotemporal change in coupling and discuss the accumulated strain balance. One of the most powerful data is the dense GNSS observation network, named GEONET, since the mid-1990s, maintained by Geospatial Information Authority of Japan (GSI). GEONET data revealed two long-term slow slip events (LSSEs) in the region; one was from mid-2000 to mid-2005 (e.g., Suito and Ozawa, 2009), and the other was from 2013 to 2016 (e.g., Ozawa et al., 2016). LSSEs are regarded as the stress release process without seismic waves, and we can also interpret them just as the temporal change in the interplate coupling. Ochi and Kato (2013) adopted this point of view and revealed that the coupling rate at some portion of the plate interface after 2000-2005 LSSE did not recover to the pre-event rate. Although we could not use GNSS data before the 1990s, many geodetic data were accumulated. I analyzed leveling data from 1981 to 1999 and length change data between 1974 and 1992, which were also obtained by GSI. These data showed fluctuation in the vertical displacement rate, indicating that at least two LSSEs were around 1987-1990 and 1983. Because the vertical displacement patterns in the 1987-1990 LSSE and 2000-2005 LSSE are clearly different, the source area of the 1987-1990 LSSE should be spread to the east portion of the 2000-2005 LSSE. These relatively small LSSEs are also regarded as the fluctuation of the interplate coupling and should be discussed from the aspect of strain accumulation.