Large-Scale Crustal Velocity Field for Eastern Turkey Determined by InSAR
Walters, Richard J.1; Parsons, Barry2; Wright, Tim J.1
1University of Leeds, UNITED KINGDOM; 2University of Oxford, UNITED KINGDOM
Tectonic deformation in Eastern Turkey is dominated by strain localisation on two major strike-slip faults; the North Anatolian Fault (NAF) and the East Anatolian Fault (EAF). Interferometric Synthetic Aperture Radar (InSAR) is a satellite remote-sensing tool that is well suited to generating high-resolution maps of crustal strain over such actively deforming regions. Here we use InSAR to map interseismic strain across the Eurasian-Arabian plate boundary zone in Eastern Turkey, covering both the NAF and the EAF.
Most previous InSAR interseismic studies of the NAF have only used descending track data, and in these studies it was therefore necessary to assume purely horizontal, fault-parallel motion in modelling deformation. The slip rate of the EAF has been the focus of only a few geological and geodetic studies, and InSAR has not previously been used to measure interseismic strain accumulation across this fault.
We construct ~400 Envisat interferograms on three descending and two ascending tracks in Eastern Turkey, covering both the NAF and EAF. We use these data to generate five line-of-sight velocity maps (ratemaps) using the ð-RATE software package (Wang et al., GRL, 2009), which implements a multi-interferogram network approach. We find that the five InSAR ratemaps agree best in overlapping regions when all interferograms are first corrected for atmospheric effects using model outputs from the ERA-Interim global atmospheric model (Jolivet et al., GRL, 2011).
From these five overlapping ratemaps, we model elastic strain accumulation for both the NAF and EAF, and calculate slip rates of 20±3 mm/yr and 10±2 mm/yr respectively, with associated locking depths of 16±9 km and 13±4 km. We then use these InSAR ratemaps together with a compilation of GPS data in order to calculate a velocity field for Eastern Turkey. We find that the velocity field derived from InSAR and GPS data significantly reduces the uncertainty of east-west velocities when compared with the velocity field derived from GPS data alone, and shows that strain is mainly localised across the NAF and EAF. We also calculate that there is negligible differential vertical motion across the NAF and EAF, and so the common assumption of purely horizontal motion is justified. This lack of vertical deformation across Eastern Turkey also supports the idea that there is no `Arabian push' that contributes to Anatolian motion, and that the westwards movement of Anatolian crust is driven only by differences in gravitational potential energy between the Anatolian Plateau and the Hellenic trench.