Comprehensive Investigation of Capabilities of the Left-Looking InSAR Observations in Coseismic Surface Deformation Mapping and Faulting Model Estimation Using Multi-Pass Measurements: An Example of the 2016 Kumamoto, Japan Earthquake

Ying-Hui Yang,Jyr-Ching Hu,Qiang Chen,Lang Xu,Jing-Jing Zhao,Qian Xu,Hao-Liang Li

doi:10.3390/rs13112034

Abstract

We here present an example of the 2016 Kumamoto earthquake with its coseismic surface deformation mapped by the ALOS-2 satellite both in the right- and left-looking observation modes. It provides the opportunity to reveal the coseismic surface deformation and to explore the performance of the unusual left-looking data in faulting model inversion. Firstly, three tracks (ascending and descending right-looking and descending left-looking) of ALOS PALSAR-2 images are used to extract the surface deformation fields. It suggests that the displacements measured by the descending left-looking InSAR coincide well with the ascending right-looking track observations. Then, the location and strike angle of the fault are determined from the SAR pixel offset-tracking technique. A complicated four-segment fault geometry is inferred for explaining the coseismic faulting of the Kumamoto earthquake due to the interpretation of derived deformation fields. Quantitative comparisons between models constrained by the right-looking only data and by joint right- and left-looking data suggest that left-looking InSAR could provide comparable constraints for geodetic modelling to right-looking InSAR. Furthermore, the slip model suggests that the series of events are dominated by the dextral strike-slip with some normal fault motions. The fault rupture initiates on the Hinagu fault segment and propagates from southwest to northeast along the Hinagu fault, then transforms to Futagawa fault with a slip maximum of 4.96 m, and finally ends up at ~7 km NW of the Aso caldera, with a rupture length of ~55 km. The talent of left-looking InSAR in surface deformation detection and coseismic faulting inversion indicates that left-looking InSAR can be effectively utilized in the investigation of the geologic hazards in the future, same as right-looking InSAR.

Highlights

The productions from the Interferometric synthetic aperture radar (InSAR) technique suggest that the descending left-looking InSAR deformation pattern presents a high consistency with the ascending right-looking track
Several clear displacement discontinuities have been recognized from deformation fields measured by the pixel offset-tracking (PO) technique
A complex fault system including four segments is constructed to estimate the slip model of the seismicity, among which the dip direction of one fault segment is opposite to the other three segments

Summary

Introduction

Interferometric synthetic aperture radar (InSAR) has been proved as a promising spacegeodetic technique, which can provide a spatially high density of ground observations for characterizing earthquake mechanism and co-seismic ground deformation as data constraints [1,2,3,4,5,6]. Direction have significantly limited the capability of the InSAR technique in mapping complete surface displacements and, further, have confined the geodetic modelling of seismic ruptures. It is known that InSAR LOS measurements are insensitive to the N-S. The joint utilization of multiple SAR acquisitions from different viewing directions are adopted to better express the ground deformation pattern and to better constrain the earthquake source modelling; it has a drawback: the majority of SAR data are generally produced in the right-looking mode. It should be noted that large uncertainties might be induced in such a strategy when the investigated objects are the strike-slip faults in nearly N-S direction and dip-slip faults in nearly E-W direction [7]

Methods

Results

Conclusion