Possible Long-term SSEs in the Tokai Area, Central Japan, After 1981: Size, Duration, and Recurrence Interval

Abstract:

The long-term slow slip event (LSSE) in the Tokai area, central Japan, from mid-2000 to mid-2005 [Suito and Ozawa (2009)], had continued five years, which was much longer than other LSSEs around the world [e.g. Schwartz and Rokosky (2007)]. After the termination of the SSE in 2005, no obvious long-term SSE was detected and that makes difficult to discuss a recurrence interval of the events. In order to reveal whether the event repeats or not, and if it repeats, to clarify the interval and a temporal and spatial change of the coupling and the LSSE, I analyzed a leveling data from 1981 to 1999 -- before the era of GNSS -- and deduced spatial patterns of the vertical crustal deformation rate.
The deduced rates show two sorts of spatial patterns and the patterns appear alternately. One of them resembles the pattern during the LSSE between 2000 and 2005. Summing up the results and accounting for the estimation errors, it is clear that there are at least three events in the last thirty years; 2000-2005 (already and well known event), 1987-1990, and around 1983. The 2000-2005 event is the biggest and longest one, while 1983 event is the smallest and shortest one in the three events. It suggests that the duration of the event is longer, the interval to the next event becomes longer, and that there are some relationships between the size, duration time, and the recurrence interval of the events. These features are very unique for the Tokai LSSEs compared with those in the other regions such as the Bungo Channel and Cascadia.