Detection of Ground Surface Deformation Caused by the 2016 Kumamoto Earthquake by InSAR using ALOS-2 Data

Abstract

SAR interferometry (InSAR) analysis of operational L-band SAR satellite of Japan, ALOS-2, reveals a series of coseismic crustal deformations caused by the 2016 Kumamoto Earthquake (April 14-16, 2016). Large coseismic deformation of over 10 centimeters due to the two large foreshocks and over 2 meters due to the mainshock can be clearly identified on the SAR interferograms as well as postseismic deformation up to a few centimeters. These displacements are concentrated around Futagawa-Hinagu fault zone which is a known active fault in Kyushu Island. 2.5-D displacements, more specifically quasi-east-west and quasi-vertical displacements due to the mainshock are also estimated from two interferograms observed from both east and west directions. The estimated displacements are consistent with those of ground GNSS observations. The sequence of the earthquakes causes significant distortion in the geodetic datum of Japan around the focal area, and thus positions of geodetic control points, which are fundamental infrastructure for implementing the datum needed to be revised as soon as possible. The area of the deformation could be promptly identified from the interferograms, and the control points which needed to be revised were quickly determined from the interferograms without any additional ground observation.