Application of Insar technique to study surface deformations related to earthquakes
Student name: Mr Gudipati Raghu Ram
Guide: Mr Chander Kumar Singh
Year of completion: 2012
Host Organisation: Space Applications Centre, ISRO, Ahmedabad
Supervisor (Host Organisation): Dr Sreejith K. M.
Abstract: Synthetic Aperture Radar Interferometry (InSAR) is a technique that permits remote detection
of deformation on the Earth's surface, and has been used extensively to measure crustal
deformation associated with earthquakes, volcanic activity, land subsidence etc. InSAR has the
potential to map millimeter-scale ground deformation over tens of kilometers at a resolution of
a few meters and is particularly sensitive to vertical displacements. In this study, co-seismic
deformation of April 4th 2010 Mw 7.2 El Mayor-Cucapah earthquake of Baja California,
Mexico is investigated in detail using InSAR technique. Further, an attempt has been made to
map inter-seismic deformation along major faults of Kachchh rift basin, Gujarat India.
The co-seismic deformation field of April 4th 2010 Mw 7.2 El Mayor-Cucapah earthquake was
mapped using ALOS- PALSAR interferogram. The interferogram reveals rupture propagation
mainly along the NW-SE trending Indiviso Fault plane. In general, the observed LOS
displacement is negative towards southwest of the fault indicating upliftment and positive
towards northeast indicating subsidence. The magnitude of net LOS displacement is found to be
around 1000 mm. On close observation, the deformation pattern further revealed the presence of
one more fault plane with reverse geometry to the south of the Indiviso Fault system and also a
minor fault at the northern tip of this fault system. The earthquake source parameters and fault
geometry were further constrained by forward modeling based on the dislocation formulation due
to a finite source rupture patch in elastic half-space. Source parameters of 4th 2010 Mw 7.2 El
Mayor-Cucapah earthquake and the three major aftershocks as provided by GCMT solution were
utilized to build an initial model. This model was observed to be highly over estimating the
deformation. The depth and slip parameters of the fault planes were then iteratively changed to
arrive at the final model after comparing with the InSAR deformation. The RMS error and
correlation coefficient of the final model (RMSE= 271 mm, R2 = 0.75) are considerably improved
when compared with the initial model (RMSE = 370 mm, R
2 = 0.6). The fault geometry and
earthquake parameters derived from the final model clearly suggests a complex rupture
propagation along multiple fault systems after the April 4th 2010 Mw 7.2 El Mayor-Cucapah
earthquake. The present study clearly demonstrates how remote sensing data sets can be
effectively used to study complex tectonic process associated with earthquakes.
InSAR application for monitoring inter-seismic deformation was tested in Kachchh region.
EnviSAT ASAR data between 2004-2007 were utilized to generate 16 interferograms of
perpendicular baselines ranging from 0 m to 500 m. These interferograms were stacked based
on minimum baseline and maximum time-period criteria to determine the rate of deformation.
The stacked interferograms were analyzed separately for periods 2004-2005, 2005-2006 and
2005-2007 for detecting inter-seismic deformation signals. This analysis clearly revealed
deformation along a part of the Kachchh Mainland Fault (KMF) in 2005-2006 time periods.
The LOS displacement is negative (~-20 mm) to the south of KMF indicating upliftment and
positive (~20 mm) to the north of KMF indicating subsidence. This deformation may be due to
creeping movement along the KMF. Further studies are required to understand mechanism of
creeping movement along KMF and its tectonic implications.
Key Words: InSAR, crustal deformation, earthquakes, deformation modeling
