Structure of the northwestern North Anatolian Fault Zone imaged via teleseismic scattering tomography

Abstract

Summary Information on fault zone structure is essential for our understanding of earthquake mechanics, continental deformation and seismic hazard. We use the scattered seismic wavefield to study the subsurface structure of the North-Anatolian Fault Zone (NAFZ) in the region of the 1999 İzmit and Düzce ruptures using data from an 18-month dense deployment of seismometers with a nominal station spacing of 7 km. Using the forward- and back-scattered energy that follows the direct P-wave arrival from teleseismic earthquakes, we apply a scattered wave inversion approach and are able to resolve changes in lithospheric structure on a scale of 10 km or less in an area of about 130 km by 100 km across the NAFZ. We find several crustal interfaces that are laterally incoherent beneath the surface strands of the NAFZ and evidence for contrasting crustal structures either side of the NAFZ, consistent with the presence of juxtaposed crustal blocks and ancient suture zones. Although the two strands of the NAFZ in the study region strike roughly east-west, we detect strong variations in structure both north-south, across boundaries of the major blocks, and east-west, parallel to the strike of the NAFZ. The surface expression of the two strands of the NAFZ is coincident with changes on main interfaces and interface terminations throughout the crust and into the upper mantle in the tomographic sections. We show that a dense passive network of seismometers is able to capture information from the scattered seismic wavefield and, using a tomographic approach, to resolve the fine scale structure of crust and lithospheric mantle even in geologically complex regions. Our results show that major shear zones exist beneath the NAFZ throughout the crust and into the lithospheric mantle, suggesting a strong coupling of strain at these depths.

Depth‐Dependent Anisotropy Along Northwest Segment of the North Anatolian Fault Zone: Evidence for Paleo‐Tectonic Structures Contributing to Overall Complexity

“…Further validation of our harmonic energy estimates comes from Rost et al. (2021) that suggested a more homogeneous crustal structure in the Armutlu Peninsula, which is confirmed by our low harmonic energy distribution resolved for upper crustal depths for this region. The NA inversion in this study, yielded well‐constrained models with anisotropic trend and strike of fast plane estimates consistent with geomorphological observations and existing knowledge of neo‐tectonic features.…”

Imaging the Crustal and Upper Mantle Structure of the North Anatolian Fault: A Transmission Matrix Framework for Local Adaptive Focusing

“…The reflectivity is disrupted around 40.75°N suggesting the presence of a step in the Moho below the Northern strand. The latter observation is in agreement with previous studies (Jenkins et al., 2020; Rost et al., 2021). Below the Moho, reflective structures are observed, mainly beneath AA and IZ, in agreement with Kahraman et al.…”

“…At the east of the Sea of Marmara, the Moho depth was reported to be between 30 and 35 km (Vanacore et al, 2013;Zor et al, 2003). A deepening of the Moho was identified (∼40 km) in the IZ by The latter observation is in agreement with previous studies (Jenkins et al, 2020;Rost et al, 2021). Below the Moho, reflective structures are observed, mainly beneath AA and IZ, in agreement with Kahraman et al (2015).…”

“…Below the Moho, reflective structures are observed, mainly beneath AA and IZ, in agreement withKahraman et al (2015). These findings, supported with other studies(Jenkins et al, 2020;Kahraman et al, 2015;Papaleo et al, 2018;Rost et al, 2021), suggest that the NNAF cuts though the entire crust and reaches the upper mantle(Jenkins et al, 2020;Kahraman et al, 2015;Papaleo et al, 2018;Rost et al, 2021). A signature of the NAFZ in the mantle has also been proposed by the long period analysis ofFichtner et al (2013).…”

Hydration State and Rheologic Stratification of the Lithospheric Mantle Beneath the North Anatolian Fault, Turkey

“…(2013) receiver function analysis and Rost et al. (2021) teleseismic scattering tomography; the lithosphere‐asthenosphere boundary (LAB) depth of 80 km is from Aldanmaz et al. (2005).…”