InSAR observations of the 2009 Racha earthquake, the Republic Georgia

Abstract. Central Georgia is an area strongly affected by earthquake and landslide hazards. On 29 April 1991 a major earthquake (Mw = 7.0) struck the Racha region in the republic Georgia, followed by aftershocks and significant afterslip. The same region was hit by another major event (Mw = 6.0) on 7 September 2009. The aim of the study reported here was to utilize geodetic data as synthetic aperture radar interferometry (InSAR) to improve a knowledge about the spatial pattern of deformation due to the earthquakes in the seismic active central Georgia. There were no actual earthquake observations by InSAR in Georgia. We used the multi-temporal ALOS L-band InSAR data to produce interferograms spanning times before and after the 2009 earthquake. We detected a local uplift around 10 cm in the interferogram near the earthquake's epicenter whereas evidence of surface ruptures could not be found in the field along the active thrust fault. We simulated a deformation signal which could be created by the 2009 Racha earthquake on the basis of local seismic records and by using an elastic dislocation model. The observed InSAR deformation is in good agreement with our model. We compared our modeled fault surface of the September 2009 with the April 1991 Racha earthquake fault surfaces, and identify the same fault or a sub-parallel fault of the same system as the origin. The patch that was active in 2009 is just adjacent to the 1991 patch, indicating a possible mainly westward propagation direction, with important implications for future earthquake hazards.