8:45 AM - 9:00 AM
[J06-1-02] Long-term slow slip events in the Tokai region, central Japan, before 2000
The Tokai region, central Japan, has been subjected to many large earthquakes due to the interplate coupling. In order to monitor the crustal deformation in the interseismic period, many kinds of geodetic observations have been conducted. The dense GNSS observation network, named GEONET in Japan since the mid-1990s maintained by Geospatial Information Authority of Japan (GSI), 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 early 2013 and seems to be still ongoing (Ozawa et al., 2016). Ozawa et al. (2016) mentioned that the center of the the ongoing event is near Lake Hamana, which is the south of the center of the 2000-2005 event, and the released seismic moment of the ongoing event will be smaller than the size of the 2000-2005 event. Their result suggests that the LSSEs in the Tokai region are repeating phenomena with variation in size and occurring place.
In order to reinforce the suggestion, I analyzed leveling data from 1981 to 1999 and length change data between 1974 and 1992, which were also obtained by GSI . The network adjusted leveling data show fluctuation in the vertical displacement rate at the inland benchmarks with respect to the benchmark at Omaezaki cape, the nearest site from the trench and show that at least two LSSEs around 1987-1990 and 1983. Compared with 2000-2005 event, the 1987-1989 event is smaller and the 1983 event is the smallest.
The 1987-1990 event shows clearer difference in vertical the displacement pattern with respect to that of the 2000-2005 event. It support the possibility of the variation in the occurring place. Although a simple forward modeling using rectangular source fault for the 1987-1990 event show that the amount of released seismic moment was about Mw 6.6, which was smaller than the 2000-2005 event done, the model cannot explain the difference in displacement pattern and more sophisticated model is required.
In order to reinforce the suggestion, I analyzed leveling data from 1981 to 1999 and length change data between 1974 and 1992, which were also obtained by GSI . The network adjusted leveling data show fluctuation in the vertical displacement rate at the inland benchmarks with respect to the benchmark at Omaezaki cape, the nearest site from the trench and show that at least two LSSEs around 1987-1990 and 1983. Compared with 2000-2005 event, the 1987-1989 event is smaller and the 1983 event is the smallest.
The 1987-1990 event shows clearer difference in vertical the displacement pattern with respect to that of the 2000-2005 event. It support the possibility of the variation in the occurring place. Although a simple forward modeling using rectangular source fault for the 1987-1990 event show that the amount of released seismic moment was about Mw 6.6, which was smaller than the 2000-2005 event done, the model cannot explain the difference in displacement pattern and more sophisticated model is required.