GPS data analysis of the long term slow slip event in the Tokai region, central Japan, since 2013.

Abstract:

 

Continuous geodetic observation networks have detected transient crustal deformation associated with various types of slow slip events (SSEs) in subduction zones worldwide. In this study, we report a long term SSE that occurred in the Tokai region, central Japan, since 2013.

GPS time series from the continuous GPS network GEONET shows the post-seismic deformation after the 2011 M9 Tohoku earthquake. Therefore, to extract slow slip signals from the time series, we must remove the post-seismic effect from the time series. For this purpose, we approximate the post-seismic deformation by the sum of exponential and logarithmic functions and subtract the estimated post-seismic deformation from the GPS time series.

We then applied a modified version of the Network Inversion Filter [Fukuda et al., 2008], which is a time-dependent inversion method to estimate the spatial and temporal distribution of fault slip from geodetic data. This method employs time-varying temporal smoothing of slip and slip rate to reduce oversmoothing of rapid changes of slip rate. Applying the method to the data from the 177 sites in the Tokai region for the period from 2008 to 2015, we were able to estimate the time evolution of daily cumulative slip and slip rate on the Philippine Sea plate. Cumulative slip from 1 January 2013 to 30 April 2015 was estimated to be 4cm around Lake Hamana. Moreover, we detected a short-term SSE near the Ise Bay for the period from January 20 to February 9, 2014. The maximum moment rate was estimated to be 5×10¹⁹ Nm/yr in 25 January 2014. We will discuss the spatiotemporal relationship between the long-term and short-term SSEs.