A magnitude 6.6 earthquake occurred in the Aegean Sea on 20 July 2017, affecting the Greek island of Kos and Bodrum in south-west Turkey. Images from the Copernicus Sentinel-1 mission were used to map the ground deformation, providing valuable data for analysis.
The earthquake was shallow (10km in depth) so the deformation at ground surface was expected in the order of a few tens of centimetres. However, the offshore location of the epicenter provided limited seismological data for locating the seismic fault and imaging its geometry. Seismology was used to determine that the fault plane was striking approximately east-west, however the dip-direction was ambiguous because of the lack of adequate near-field stations. Geological data indicated both north- and south-dipping normal faults inside the greater region of Kos – Gulf of Gokova (Turkey), but little information existed for the offshore region between Kos and Bodrum.
A team of researchers from the National Observatory of Athens (Greece) and Ecole Normalle Superierre (France) processed Sentinel-1 images acquired before and after the earthquake, in order to produce an interferogram that would provide geodetic constraints of fault location and its geometry. The co-seismic pair became available after the Sentinel pass on 24 July over the region and on 25 July the interferograms were produced.
The imaged deformation (shown below) occurred mainly on the Karaada islet (offshore Bodrum) and reached about 20cm in the line-of-sight. Preliminary modeling of the displacements using a linear approach and elastic parameters showed that the offshore fault was dipping towards North at an angle of about 40 degrees. The fault dimensions were 16km (long) by 11km (wide) and the total slip reached 1.5m. Without the Sentinels and InSAR techniques it would have been very difficult to constrain the seismic fault.
Sentinel-1A wrapped interferogram descending orbit showing several seismic fringes on the islet of Karaada (Turkey). The yellow star indicates the earthquake epicentre (NOA revised location)
Copyright: Contains modified Copernicus Sentinel-1 data processed by Athanassios Ganas, Panagiotis Elias, Sotiris Valkaniotis (NOA) and Pierre Briole (ENS)