Spatiotemporal Evolution of Long‐ and Short‐Term Slow Slip Events in the Tokai Region, Central Japan, Estimated From a Very Dense GNSS Network During 2013–2016

Abstract

AbstractWe analyzed Global Navigation Satellite System (GNSS) data from 1 January 2008 to 31 January 2016 for the Tokai region of the Nankai subduction zone, in order to study long‐ and short‐term slow slip events (SSEs) on the subduction interface. The dataset included our new temporary stations to obtain high resolution observations with station spacing of about 5 km. Long‐ and short‐term SSEs have been reported in the Tokai region, over the past two decades. It is difficult to directly compare those SSEs because long‐term SSEs were observed by GNSS, while short‐term SSEs were mainly observed by tiltmeters and strainmeters. We applied a time‐dependent inversion with improved temporal resolution to GNSS data and successfully obtained the spatiotemporal evolution of long‐ and short‐term SSEs. Our results show the very slow and stable slip of a long‐term SSE with Mw 6.6, along with several episodes of accelerated slip associated with short‐term SSEs (Mw 6.0–6.1). Our results showed the details of the migrating slip patterns and slip rates for the short‐term SSEs and possible relation with low frequency tremor (LFT). LFT is more associated with smaller magnitude short‐term SSEs rather than the larger long‐term SSEs. However, the maximum daily slip rates for short‐term SSEs are an order of magnitude larger than those for the long‐term SSEs. This suggests an explanation that the LFT may be directly related to the loading of the plate interface by the short‐term SSEs.