Comparative Analysis of Geodetic Strain Rate Field Around Anatolia: GPS vs InSAR Models

The evergrowing geodetic studies in the applications of GPS and InSAR are presenting a great potential to better map out interseismic velocity and strain rate fields in a given region. These methods allow scientists to find ongoing deformation type and rate on active faults with great precision, which is in fact quite important in seismic hazard analyses in the sense of earthquake source characterization. With this purpose, we made a GPS velocity compilation of Türkiye, Greece and other neighboring countries first, then the InSAR derived velocity field was merged to create one combined velocity field of the area, using a least-squares approach. Afterwards, the active strain rate field of Türkiye and its vicinity is calculated using GPS, InSAR and the merged data.

Resultant maximum shear strains derived from GPS data varies between 80 and 180 nstrain/yr along North Anatolian Fault (NAF), which is slightly higher than InSAR based findings ranging between 60 and 140 nstrain/yr. Both results display relatively low shear strains on the locked Marmara segment of NAF and highest values on Ganos, İzmit, Düzce, Bolu and Gerede segments possibly due to the presence of postseismic signals. Towards east, shear strains are lower but InSAR derived ones increase noticeably where NAF curves and branches into multiple fault splays near Niksar.

Resultant anomalies of InSAR based dilational strains suffer from higher degrees of smearing in north-south direction and differ more noticeably. Especially, InSAR indicates elevated and widespread dilations throughout Thrace Basin and Karlıova Junction that contradicts the GPS derived strains, possibly due to temporal variations. Western Anatolia and İskenderun Gulf are represented by large positive dilational strains in both datasets which suggest relatively fast active extension. In Western Anatolia, Menderes and Gediz grabens are both characterized by high amounts of dilation that reaches up to a  maximum of 80 nstrain/yr at the western section of Menderes Graben.

Principal strain directions computed from GPS and InSAR are similar within fast deforming areas but differ largely at areas where strains are minimal such as Central Anatolia which implies reduced precision in slowly deforming zones. All in all, strain rate field obtained from GPS compilation shows better fit with mapped active faults and earthquake mechanisms. Thus, resultant strain rate field estimations using only InSAR data shall be used with caution and rather be combined with sufficient number of GPS recordings if applicable.

Keywords: GPS, InSAR, Interseismic Strain Field, Shear Strain, Dilation, Eastern Mediterranean