Temporal variation in scattering and intrinsic attenuation due to earthquakes in East Asia.

Separated attenuation values have not been used in post-seismic variation research, although the scattering attenuation (Qs-1) parameter that can be used to estimate crustal inhomogeneity due to cracks. In this study, three earthquakes that occurred in Kumamoto (M7.3), Tottori (M6.6), and Gyeongju (M5.8) in 2016 were investigated by applying a multiple lapse time window analysis to seismograms recorded before and after the events. At a low frequency, significantly greater variation of the Qs-1 value was observed than the intrinsic attenuation (Qi-1) for the Kumamoto earthquake, whereas similarly large variation was observed for the Gyeongju earthquake. For the surrounding Kumamoto earthquake area of increased attenuation, even higher decreases in Qs-1 and Qi-1 were also observed. The increases occurred within a two year-period after mainshock. The large increases in attenuation, corresponding to regions with high peak ground acceleration, were limited to the basin area with an elevation below 500 m. Furthermore, post-seismic increases in attenuation values were found to correlate with the magnitude and length of the quiet periods of the earthquakes. From this study, Qs-1 and Qi-1 were shown as new parameters that can quantitatively measure the post-seismic deformation due to crustal earthquake.