Distribution of interseismic coupling along the North and East Anatolian Faults inferred from InSAR and GPS data

Abstract

The North Anatolian Fault (NAF) is one of the most hazardous fault in the world. After decades of low seismicity, the M w 6.8 Elazig earthquake (January 24, 2020) has recently reminded us that the East Anatolian Fault (EAF) is also capable of producing large earthquakes. To better estimate the seismic hazard associated with these two faults, we jointly invert Interferometric Synthetic Aperture Radar (InSAR) and GPS data to image the spatial distribution of interseismic coupling along the eastern part of both the North and East Anatolian Faults. We perform the inversion in a Bayesian framework, enabling to estimate uncertainties on both long-term relative plate motion and coupling. We find that coupling is high and deep (0-20 km) on the NAF and heterogeneous and superficial (0-5 km) on the EAF. Our model predicts that the Elazig earthquake released between 200 and 250 years of accumulated moment, suggesting a bi-centennial recurrence time.

High‐Resolution Surface Velocities and Strain for Anatolia From Sentinel‐1 InSAR and GNSS Data

“…This is also where the east-west velocity contrast is most apparent (Figure 3b). While there is some seismicity associated with the EAF (Figure 3a), the recently compiled 1900-2012 earthquake catalog for Turkey (Kadirioğlu et al, 2018) indicates that the associated magnitudes and thus total moment release are much lower than those along the NAF, supporting the notion that less strain is accumulating along the EAF than along the NAF (Bletery et al, 2020). The 24 January 2020 M w 6.7 Elaziğ earthquake (Melgar et al, 2020) occurred on the portion of the EAF where we resolve both an east-west velocity gradient and elevated strain rates on the order of~70 nanostrain/year (Figures 3 and 4).…”

Kinematics and Dynamics of the 24 January 2020 Mw 6.7 Elazig, Turkey Earthquake

“…However, all of the InSAR tracks used by Cavalié and Jónsson (2014) and Walters et al (2014) do not show any sharp displacement discontinuities, indicating that the fault creep should not have reached the surface during the InSAR observation period and is thus possibly a transitory phenomenon. Taking all the above into account, we believe that besides imparted by past events (Nalbant et al, 2002), heterogeneous stress distribution is being built up constantly during the interseismic period on locked patches along EAFZ as revealed by a recent study by Bletery et al (2020), which can then fail separately or collectively during earthquakes (Kaneko et al, 2010), and this is probably the main reason for the irregularity of earthquake intervals along EAFZ.…”

“…A number of previous studies have also tried to estimate the fault locking depth and slip rate using InSAR and GNSS velocity fields (e.g., Bletery et al, 2020; Cavalié & Jónsson, 2014; Walters et al, 2014), which contribute to evaluate the strain building and identify the slip deficits. With regard to the geodetic approach, a long outstanding problem is that there exists a trade‐off in the estimation of slip rates and locking depth (Savage & Burford, 1973).…”

A Stochastic View of the 2020 ElazığMw6.8 Earthquake (Turkey)

“…We compare the seismic moment accumulated since the possible last historic rupture of the Pütürge segment (1905) with the seismic moment released during the 2020 Elazığ earthquake (Figure 4d). To do so, we calculate the seismic moment for the area ruptured by the event according to our slip model, and account for uncertainties in ruptured area ( σ = 3 km 2 ), shear modulus ( μ = 2.8 ± 0.3 10 1 GPa), coupling and slip rates (according to Bletery et al., 2020). The moment released by the 2020 event is largely greater than the one accumulated since 1905 (2.34 ± 0.25 ≫ 0.72 ± 0.19 10 19 N m).…”

“…The EAF has a complex geometry divided into several main segments, each of them characterized by bends, pull‐apart basins or compressional structures (e.g., Duman & Emre, 2013), and also comprises multiple secondary subparallel and seismically active structures delineating a 50‐km‐wide fault zone (e.g., Bulut et al., 2012). The EAF accommodates a displacement of 9–15 mm/yr (Aktug et al., 2016; Bletery et al., 2020; Cavalié & Jónsson, 2014; Cetin et al., 2003; Reilinger et al., 2006), with creep dominantly at depths greater than 5 km (Bletery et al., 2020; Cavalié & Jónsson, 2014). As a comparison, the NAF shows creep rates around 20–25 mm/yr below a locking depth of 7–25 km (e.g., Cakir et al., 2014; Hussain et al., 2018; Kaneko et al., 2013; Walters et al., 2011; Wright et al., 2001).…”