Detection of small crustal deformation caused by slow slip events in southwest Japan using GNSS and tremor data

We stacked daily Global Navigation Satellite System (GNSS) displacement increments in southwest Japan to detect the cumulative crustal deformation accompanying non-volcanic low-frequency tremors from April 1, 2004 to December 31, 2009, which are difficult to identify for individual slow slip events (SSEs). We successfully detected the crustal deformation associated with the tectonic stress releases coincident with tremor activity, which was larger than that caused by short-term SSEs detected in previous studies. To investigate the characteristics of the detected crustal deformation, we estimated the parameters of a rectangular fault model in segments along the Nankai Trough using a non-linear inversion method. Consequently, we obtained results that were concordant with those of previous studies and positive linear correlations between the moment and tremor energy in some segments. The linear regression slopes differed, reflecting the fact that the excitation efficiency of the tremors resulting from slow slip was different for each segment. Our results suggest that tremor activity serves as a proxy for SSEs, reflecting the different characteristics of SSEs in segments.