Abstract
AbstractThe North Anatolian Fault (NAF) is a major tectonic feature in the Middle East and is the most active fault in Turkey. The central portion of the NAF is a region of Global Navigation Satellite Systems (GNSS) scarcity. Previous studies of interseismic deformation have focused on the aseismic creep near the town of Ismetpasa using radar data acquired in a single line‐of‐sight direction, requiring several modeling assumptions. We have measured interseismic deformation across the NAF using both ascending and descending data from the Envisat satellite mission acquired between 2003 and 2010. Rather than rejecting incorrectly unwrapped areas in the interferograms, we develop a new iterative unwrapping procedure for small baseline interferometric synthetic aperture radar (InSAR) processing that expands the spatial coverage. Our method corrects unwrapping errors iteratively and increases the robustness of the unwrapping procedure. We remove long wavelength trends from the InSAR data using GNSS observations and deconvolve the InSAR velocities into fault‐parallel motion. Profiles of fault‐parallel velocity reveal a systematic eastward decrease in fault slip rate from 30 mm/yr (25–34, 95% confidence interval (CI)) to 21 mm/yr (14–27, 95% CI) over a distance of ∼200 km. Direct offset measurements across the fault reveal fault creep along a ∼130 km section of the central NAF, with an average creep rate of 8 ± 2 mm/yr and a maximum creep rate of 14 ± 2 mm/yr located ∼30 km east of Ismetpasa. As fault creep is releasing only 30–40% of the long‐term strain in the shallow crust, the fault is still capable of producing large, damaging earthquakes in this region.
Highlights
The North Anatolian Fault (NAF) is a major continental right-lateral transform fault located in northern Turkey
In order to understand the role that the NAF plays in regional tectonics and seismic hazard, there have been numerous estimates of the fault slip rate for the NAF using present-day deformation measured with Global Navigation Satellite Systems (GNSS) [e.g., Straub et al, 1997; Reilinger et al, 2006; Ergintav et al, 2009] or offset geological features [e.g., Hubert-Ferrari et al, 2002; Pucci et al, 2008; Kozaci et al, 2009]
Iterative Unwrapping Benefits and Limitations Our new iterative unwrapping procedure reduces the number of unwrapping errors in the overall small baseline network and improves the interferometric synthetic aperture radar (InSAR) coverage as more correctly unwrapped pixels are added to the network instead of being discarded
Summary
The North Anatolian Fault (NAF) is a major continental right-lateral transform fault located in northern Turkey. Since the 1939 Mw 7.9 Erzincan earthquake in eastern Turkey, the NAF has ruptured in a sequence of large (Mw > 6.7) earthquakes with a dominant westward progression in seismicity [Barka, 1996; Stein et al, 1997]. In order to understand the role that the NAF plays in regional tectonics and seismic hazard, there have been numerous estimates of the fault slip rate for the NAF using present-day deformation measured with Global Navigation Satellite Systems (GNSS) [e.g., Straub et al, 1997; Reilinger et al, 2006; Ergintav et al, 2009] or offset geological features [e.g., Hubert-Ferrari et al, 2002; Pucci et al, 2008; Kozaci et al, 2009]. There have been several interferometric synthetic aperture radar (InSAR)-derived estimates of the fault slip rate, which have focused on the western or eastern regions of the NAF where the InSAR coherence is better [e.g., Wright et al, 2001a; Cakir et al, 2005; Walters et al, 2011; Kaneko et al, 2013; Cakir et al, 2014; Cetin et al, 2014; Walters et al, 2014; Cavalié and Jónsson, 2014; Hussain et al, 2016]
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