Coseismic and Postseismic Crustal Deformation Associated With the 2016 Kumamoto Earthquake Sequence Revealed by PALSAR-2 Pixel Tracking and InSAR

Abstract

Coseismic and postseismic crustal deformations caused by earthquake episodes are important in understanding the mechanisms of these episodes as well as the fault rheology near an epicentral area. Specifically, interferometric synthetic aperture radar (InSAR) and synthetic aperture radar (SAR) pixel tracking can depict high-resolution crustal deformation fields associated with earthquakes and volcanic activities without installing on-site observation instruments. In this study, we investigate the coseismic and postseismic near-fault crustal deformations associated with the 2016 Kumamoto earthquake sequence in southwest Japan using ALOS-2/PALSAR-2 (Phased Array-type L-band SAR-2) data. Coseismic three-dimensional (3-D) displacement fields inferred from PALSAR-2 pixel tracking data showed 1.6 m of horizontal displacements and 2 m of subsidence at maximum, despite the mainshock focal mechanism that was dominated by strike-slip components with N-S extension axes. The locations of large displacement variations along surface ruptures due to the mainshock were almost identical to a region where infrastructure was damaged, thus implying the generation of strong ground seismic waves. By using conventional InSAR stacking, we inferred two independent quasi-east-west and quasi-vertical displacement fields as cumulative postseismic deformations following the mainshock over a period of about 2 years. The near-fault postseismic deformation represented complicated displacement characteristics that could not be explained by a single physical process. Deformation signals around Aso volcano were interpreted by the effects of postseismic physical processes as well as geological heterogeneous structures.