Strain accumulation and release associated with the occurrence of SSEs in the subduction zones of the Japanese Islands.

We investigated the spatiotemporal changes in strain associated with the occurrence of slow slip events (SSEs) in the subduction zones of the Japanese Islands and compared the spatial distribution of both the amount of strain accumulated for the period before and during the SSEs release using time series data from the Global Navigation Satellite System (GNSS). In this study, four SSEs were analysed: the Tokai long-term SSE (2000-2005), the Boso-Oki short-term SSE (2007), and the Bungo Channel long-term SSEs (2009-2011 and 2018-2019). As a result, we found strong negative correlations for all four dilatations before and during SSE occurrence. For these dilatations, we estimated the amount of strain released at the time of occurrence of the SSE relative to that accumulated during the period prior to the SSE. The result indicates that not all the accumulated strain before the SSEs was released when the SSEs occurred. Moreover, it is highly likely that the strain released by SSE is not only due to the strain accumulation just below the SSE occurrence region, but also due to the strain accumulation on the shallower plate boundary, which is a seismogenic zone for a future megathrust earthquake.