Postseismic Deformation Following the 2016 Kumamoto Earthquake Detected by ALOS-2/PALSAR-2
Abstract We have been conducting study of postseismic deformation following the 2016 Kumamoto earthquake using ALOS-2/PALSAR-2 acquired till 2018. We apply ionospheric correction to interferograms of ALOS-2/PALSAR-2. L-band SAR gives us high coherence enough to reveal surface deformation even in vegetated or mountainous area for pairs of images acquired more than 2 years. Ionospheric disturbances are seen both in the ascending and descending images, but spatial characteristics may be different each other. Postseismic deoformation following the Kumamoto earthquake is much larger than those observed after recent inland earthquakes in Japan with GPS, which exceeds 10 cm during two years at some spots in and around Kumamoto city and Aso caldera. There are sharp changes across several coseismic surface ruptures such as Futagawa, Hinagu and Idenokuchi faults. Time constant of postseismic decay ranges from 1 month to 600 days at selected points, but that LOS changes during the first epochs or two are dominant. This result suggests multiple source of postseismic deformation. LOS changes around the Hinagu and Suinzenji faults that appeared during the mainshock in Kumamoto City may be explained with right lateral afterslip on these faults. LOS changes around the Hinagu and Idenokuchi faults cannot be explained with right-lateral afterslip, which requires another unknown source. Deformation in northern part of Aso caldera may be the result of right lateral afterslip on unknown fault.