Surface displacement estimation using space-borne SAR interferometry in a small portion along Himalayan Frontal Fault

Abstract

Earthquake is one of the most destructive natural hazards which pose a real threat to India with nearly 59% of its geographical area vulnerable to seismic disturbance of varying intensities including the capital city of the country. India has experienced several major earthquakes mainly in Himalayan region and is also considered as one of the most earthquake prone regions in the world. Therefore, during past few decades, the Himalayan region has been studied extensively in terms of present ongoing displacements. It can be believed that a better estimate of the current Himalayan convergence rate and possible rupture can improve seismic hazard evaluations. Moreover, an improved convergence rate is also necessary to estimate if any slip deficit is available to drive future earthquakes in this region. In recent years, SAR interferometry has been successfully used for generating large scale surface displacement maps in radar look direction on a dense grid and with a centimeter to millimeter accuracy. In this context, the usefulness of SAR interferometry technique and its variations for estimation of displacements has been studied and presented in this paper. To study the displacement both conventional and multi-temporal Differential SAR interferometry has been used. In order to get the 3-D surface displacement, interferogram from both ascending and descending track can be used. However, due to the unavailability of ascending track data, a well-known mathematical model also has been used. Overall average displacement rates in the present study are found to be relatively lower as compared to the reported convergence rates. From geophysical point of view, the results presented in this paper for a small area are quite promising. Several explanations have also been presented in this paper to support the results. The reported low convergence rate may be due to the occurrence of silent/quite earthquakes, aseismic slip, differential movement of Delhi Hardwar ridge, etc. Therefore, in view of the contemporary seismicity and conspicuous displacements, a study of long-term observations of this surface movement has been recommended in future.