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Atmospheric phase contribution significantly influences co-seismic surface deformation estimates from repeat pass Differential Synthetic Aperture Radar Interferometry (DInSAR). Present study investigates the contribution of the atmosphere in co-seismic deformation estimation associated with the 20 April 2013 Lushan (China) earthquake. The Lushan Earthquake occurred in the south-western segment of the Longmenshan fault zone, on the eastern margin of the Qinghai-Tibetan Plateau. Using pre- and postearthquake Radarsat-2 interferometric pair, the co-seismic deformation of the Lushan earthquake has been estimated. The tropospheric phase delay component has been estimated using tropospheric models in conjunction with surface temperature and pressure data from MODIS atmospheric products. The ionospheric phase component has been computed using the Total Electron Content (TEC) data. The net atmospheric path addition in the study area varies from 3.022 m to 4.621 m for the pre-earthquake SAR acquisition and from 2.687 m to 4.199 m for the post-event data acquisition. Comparison of the Line of Sight (LOS) displacement values computed using un-corrected and corrected interferometric data shows that the atmospheric phase component has introduced considerable contribution in the LOS displacement values. The uncorrected LOS displacement values vary from 0.902 m to −0.157 m where as those from the phase-corrected interferometric data are in the range of 0.052 m and −0.062 m. The corrected LOS displacement values show close agreement to a few GPS based co-seismic surface deformation components from published literature. Thus removal of atmospheric phase contribution is a necessary step in using repeat pass DInSAR for co-seismic surface deformation estimation.

ABSTRACT:The Indian Plate is highly dynamic in nature which in turn makes the Indo-Eurassian collision zone the foci of most of the historic large magnitude earthquakes. Processing of positional information from continuously observing reference stations is one of the space based geodetic techniques used globally and nationally to understand the crustal dynamics. The present study evaluates the dynamic nature of the Indian plate relative to its adjoining plates using the permanent GPS data (2011 to 2013) of 12 International GNSS Service (IGS), which are spread across the Indian, Eurassian, Australian, Somaliyan and African plates. The data processing was carried out using GAMIT/GLOBK software. The results indicate that the average velocity for the two IGS stations on the Indian Plate (Hyderabad and Bangalore) is 54.25 mm/year towards NE in the ITRF-2008 reference frame. The relative velocity of various stations with respect to the Indian plate has been estimated using the Bangalore station and has been found that the stations in the Eurasian plate (Lhasa, Urumqi, Bishkek and Kitab) are moving with velocity ranging from 25 to 33 mm/year in the SE direction resulting in compressional interaction with the Indian plate. This study reveals and confirms to the previous studies that the IndianEurassian-Australian Plates are moving at different relative velocities leading to compressional regimes at their margins leading to seismicity in these zones.

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