Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Nat. Hazards Earth Syst. Sci., 16, 2137-2144, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
23 Sep 2016
InSAR observations of the 2009 Racha earthquake, Georgia
Elena Nikolaeva1,a and Thomas R. Walter1 1Department 2, Physics of the Earth, Helmholtz Center Potsdam, GFZ German Research Center of Geosciences, Potsdam, Germany
anow at: Ilia State University, Tbilisi, 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 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 interferometric synthetic aperture radar (InSAR) data to improve knowledge about the spatial pattern of deformation due to the 2009 earthquake. There were no actual earthquake observations by InSAR in Georgia.

We considered all available SAR data images from different space agencies. However, due to the long wavelength and the frequent acquisitions, only the multi-temporal ALOS L-band SAR data allowed us to produce interferograms spanning the 2009 earthquake. We detected a local uplift around 10 cm (along the line-of-sight propagation) 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. 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.

Citation: Nikolaeva, E. and Walter, T. R.: InSAR observations of the 2009 Racha earthquake, Georgia, Nat. Hazards Earth Syst. Sci., 16, 2137-2144,, 2016.
Publications Copernicus
Short summary
The study of active faults is relevant to estimate the seismic hazard of the surrounding area and relies on different methods. In the last decade interferometric synthetic aperture radar (InSAR) techniques have proved to be robust tools to investigate the surface deformation caused by earthquakes. We used the multi-temporal ALOS L-band InSAR data to produce interferograms spanning times before and after the 2009 earthquake (Mw  = 6.0) in the Racha region (Georgia).
The study of active faults is relevant to estimate the seismic hazard of the surrounding area...