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 ( Q s −1 ) parameter that can be used to estimate crustal inhomogeneity due to cracks. In this study, three earthquakes that occurred in Kumamoto ( M 7.3), Tottori ( M 6.6), and Gyeongju ( M 5.8) 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 Q s −1 value was observed than the intrinsic attenuation ( Q i −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 Q s –1 and Q i –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, Q s –1 and Q i –1 were shown as new parameters that can quantitatively measure the post-seismic deformation due to crustal earthquake.