Interseismic strain accumulation across the North Anatolian Fault measured using InSAR

The North Anatolian Fault (NAF) is a major feature of Middle Eastern tectonics, facilitating the westwards 'escape' of the Anatolian block away from the Arabia-Eurasia continental collision. In order to understand the role that the NAF plays in regional tectonics it is important to accurately determine the slip rate across the fault. Many slip rate estimates for the NAF have been made over Quaternary and longer time-scales but few geodetic estimates currently exist, especially in eastern Turkey. Here we construct satellite radar interferograms using Envisat ASAR data to measure ground displacements around the NAF and hence estimate the slip rate across it. We make use of SAR data from two satellite tracks, one ascending and one descending, that overlap across the NAF, providing a check on the assumption of horizontal fault-parallel motion that has previously been used in interseismic modelling of the fault. We mitigate the effects of atmospheric errors by constructing multiple interferograms over the fault and summing them, effectively creating a longer timespan interferogram and improving the signal-to-noise ratio. We empirically correct for orbital errors by flattening the radar swaths on the Anatolian Plateau, an area with little expected deformation. Our measurements of rates of displacement are consistent with an interseismic model for the NAF where deformation occurs at depth on a narrow shear zone below a layer in which the fault is locked. We jointly invert data from both satellite tracks to solve for best fitting model parameters, estimating both the slip rate and the depth to which the fault is locked. Our best-fitting model gives a slip rate of 23 mm/yr and a locking depth of 19 km, which is in agreement with a previous estimate made from a single track of ERS SAR data (Wright et al., 2001, GRL 28, 2117-2120), and with existing GPS data. We also construct a velocity field using a combination of InSAR and GPS data for eastern Turkey.