Localized crustal deformation along the central North Anatolian Fault Zone revealed by joint inversion ofP-receiver functions andP-wave polarizations

Abstract

The North Anatolian Fault Zone (NAFZ) is a major plate boundary that separates the Eurasian Plate to the north from the Anatolian Plate to the south and is associated with powerful damaging earthquakes. Despite numerous studies of the crust and upper mantle across the NAFZ, our understanding of the exact mechanisms and distribution of deformation with depth is still limited. Accurate models of the crustal velocity structure are key to assess seismic hazard associated with strike-slip deformation. Here, we address this need by employing a novel method that jointly inverts receiver function waveforms and P-wave polarizations to recover S-wave velocity structure from the surface to the upper mantle. The method is applied to a dense teleseismic data set collected across a segment of the central NAFZ in Turkey. The results provide important new constraints on the sedimentary thickness, depth to basement and Moho discontinuity beneath the region. Our estimates of uppermost sedimentary thickness range from 0 km in some areas (e.g. in the Central Pontides) to 6 km in the Ç ankırı Basin. Smaller basins are scattered along the NAFZ. A similar pattern is observed for the basement depth, with values exceeding 10 km beneath the Ç ankırı Basin, where the Moho is shallowest with a depth of ∼32 km. The Moho reaches a maximum depth of ∼42 km beneath the Central Pontides. Most other areas have an average Moho depth of 35-38 km. The results reveal clear structural-tectonic relationships in the crust: areas of fundamentally different sedimentary and crustal architecture are bounded by faults and suture zones. The NAFZ appears to accommodate small-scale basin and basement-highs, and acts as a thickskinned (i.e. full crustal-scale) boundary between laterally displaced crustal blocks to the north and south. Seismicity clusters are centred on areas of low Vp/Vs ratios that may be representative of weak zones.

New Insights Into Crustal Properties of Anatolia and Its Surroundings Inferred From P‐Coda Autocorrelation Inversions

“…Localized strain accumulation on a part of the NAFZ was earlier suggested as the main source for the crustal deformation during the earthquake cycle (Schiffer et al., 2019). Clear correlations between crustal properties (e.g., seismic wave speeds and attenuation) and surface features (e.g., terrane boundaries and faults) also suggest more focused deformation along the central part of the NAFZ (e.g., Gaebler et al., 2019; Schiffer et al., 2019). A qualitative inspection of our crustal thickness variations along most of the NAFZ and EAFZ suggests brittle deformation in the lower crust, as it appears relatively narrow and coupled with brittle seismogenic zones as they cut through the entire crust with usually large Moho offset reaching up to (8–9 km).…”

“…The latter may be related to broad distribution of deformation in the lower crust and upper mantle and thus surface projections of the motion along the fault is governed by shear tractions at the base of the brittle upper crust (Zhu, 2000). Localized strain accumulation on a part of the NAFZ was earlier suggested as the main source for the crustal deformation during the earthquake cycle (Schiffer et al, 2019). Clear correlations between crustal properties (e.g., seismic wave speeds and attenuation) and surface features (e.g., terrane boundaries and faults) also suggest more focused deformation along the central part of the NAFZ (e.g., Gaebler et al, 2019;Schiffer et al, 2019).…”

Isotropic and Anisotropic P Wave Velocity Structures of the Crust and Uppermost Mantle Beneath Turkey

“…High‐precision earthquake catalogs generated for the NAFZ clearly mark earthquake cluster geometries primarily focused in the upper 15–20 km depths (e.g., Poyraz et al, 2015; Sato et al, 2004; Taymaz et al, 1991). Crustal V p and V s resolved by a joint inversion of receiver functions and apparent V s curves along the central NAFZ indicate that localized strain accumulation could be the main source for the crustal deformation during earthquake cycles (Schiffer et al, 2019). Receiver function and teleseismic tomography studies performed over a small and dense passive seismic network, called DANA, at the northwestern part of the NAFZ provide fine details about the crust and upper mantle heterogeneities with a good horizontal resolution (less than 10 km).…”

“…Investigations of the structure and distribution of deformation in the crust and mantle are essential to understand the geodynamics shaping Turkey. and the Moho discontinuity is undulating:~30 km in the west and deepening eastward to~50 km in the Eastern Anatolia Plateau (e.g., Abgarmi et al, 2017;Frederiksen et al, 2015;Kahraman et al, 2015;Licciardi et al, 2018;Schiffer et al, 2019;Vanacore et al, 2013). Many tomographic studies have been conducted to reveal the 3-D seismic structures beneath Turkey.…”

“…Owing to increasing efforts in passive seismic monitoring in Turkey, the number of temporary and permanent seismic stations has increased dramatically in the past decade, which has greatly improved the station coverage and so the spatial resolution of various seismic imaging results (e.g., Biryol et al, 2011; Çubuk‐Sabuncu et al, 2017; Endrun, 2011; Fichtner, Saygin, 2013; Fichtner, Trampert, 2013; Kaviani et al, 2018; Kind et al, 2015; Portner et al, 2018; Salaün et al, 2012; Schiffer et al, 2019; Wei et al, 2019). Receiver function studies indicate that the lithosphere beneath Turkey is thin (80–100 km; Kind et al, 2015) and the Moho discontinuity is undulating: ~30 km in the west and deepening eastward to ~50 km in the Eastern Anatolia Plateau (e.g., Abgarmi et al, 2017; Frederiksen et al, 2015; Kahraman et al, 2015; Licciardi et al, 2018; Schiffer et al, 2019; Vanacore et al, 2013). Many tomographic studies have been conducted to reveal the 3‐D seismic structures beneath Turkey.…”