SAR INTERFEROMETRY FOR EARTHQUAKE INDUCED GROUND DEFORMATIONAL STUDIES

Abstract

Seismic events, mainly caused by sudden relative displacements of tectonic plates, cause deformations of the earth both inside as well as on the surface. The amount of such deformations depends upon the intensity of energy released during such seismicity. Upper crustal ground deformations cannot be measured accurately and completely without tedious manpower labor or sophisticated technology. When dealing with micro level deformations, this task becomes much more complicated. Microwave remote sensing has this capability to measure such small deformations using the approach of phase difference calculation of the backscattered waves coming to the scanner from the ground. Because of having the unique quality to penetrate clouds and having its own source of illumination, this technology can be used all the time. This microwave technique, where we use Synthetic Aperture Radar (SAR) images of the study area to quantify the extent of ground deformations taken place there, is known as Interferometric Synthetic Aperture Radar (InSAR or lfSAR). The central Kutch region of Gujarat, India experienced M7.7 earthquake in 2001, 26th January, causing large-scale ground deformations including huge loss of lives and infrastructure. Rupturing of a hidden reverse fault was the reason for this intense tectonic activity. The post seismic ground deformations, attributed to the relaxation phase of a stressed crustal layer, have been analyzed using ALOS-PALSAR InSAR pair. The InSAR pair belongs to the year 2007 and 2010, covering an area around Bhuj, falling on Kutch Mainland Fault (KMF) and Katrol Bhuj Fault (KBF). Using Adore-DORIS software interferometric images have successfully been generated covering the study area, which has allowed making interesting geological inferences. Three different regions in the study area illustrated countable visible colored fringes, indicating different amount of positive and negative ground deformations (surface motion with respect to the satellite) occurred within the InSAR data acquisition dates. Region around, to the north and east of Bhuj city showed top surface deformations of soft crustal layer of about -35cm, -35cm and 24cm, respectively. Synoptic view of interferometric image of the study area suggests two crustal fault lines running to the north and south of Bhuj city. Institute of Seismological Research (ISR) geophysical and GPS data depicts huge seismic events occurred during the year 2007-2010 and supports observational inference of clustering of interferometric fringes to the east and NE of the study area.