131 Going with the Shear - New Insights into Lithospheric Extensional and Strike-Slip Systems

This session explores key structural processes that govern the temporal, mechanical, and rheological evolution of crustal/lithospheric extensional and strike-slip systems with a focus on novel field observations, microstructural and analytical methodologies, and numerical modeling.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 217D

Lithospheric-scale Structural Controls on the Evolution of the East Anatolian Fault Zone

Paper number: 131-8
Program: Technical Sessions
Time: 3:40 PM – 3:55 PM

Authors

Abstract

The >500 km long diffuse and broadly left-lateral East Anatolian Fault Zone (EAFZ) is the southeastern portion of the Anatolia Plate tectonic escape system and represents one limb of the unstable Anatolia-Arabia-Africa triple junction. The EAFZ also represents one of the greatest seismic hazards in Türkiye, as demonstrated by the devasting Kahramanmaraş earthquake sequence in February 2023. This sequence was characterized by two major earthquakes (Mw 7.8 and 7.5) along the main and northern strands of the EAFZ that, along with associated aftershocks, had a broad spatial distribution which led to >50,000 deaths, >1 million people displaced, and >$34 billion in damage.

In this study, we use a seismic velocity model derived from the joint inversion of receiver functions and surface waves to demonstrate that the distributed nature of deformation and seismicity associated with the EAFZ is related to the evolution of the deep (>30 km) lithospheric architecture below the margin. Today, the northern strand of the EAFZ (Mw 7.5 earthquake) lies directly above where we image the strong mantle lithosphere of the underthrust Arabia Plate colliding with the weak and ductile lower crust of the Anatolia Plate. Strain associated with this deformation is being transmitted through this ductile lower crust, as expressed in seismogenic patterns and surface faulting. Restoring relative plate motion to ~5 Ma reveals that the location of this deep boundary spatially corresponds to the EAFZ's main strand (Mw 7.8 earthquake) at its inception as the major plate-bounding fault. This implies that the Arabia-Anatolia plate boundary may currently be shifting from the "main" strand of the EAFZ to its northern strand. Furthermore, we image the western edge of the Arabian lithosphere below the Adana basin, where it is aligned with deep (>30 km) strike-slip seismogenesis than can be linked to EAFZ seismicity. These observations imply that the major structural controls driving the broad deformation pattern of the EAFZ may be linked with the northward migration of the Arabia Plate at depth, which appears to ultimately control the evolution of the Anatolia-Arabia-Africa triple junction. Thus, while earthquake stress release in strike-slip systems is commonly limited to brittle failure in the upper crust (<15 km), the stresses that lead to this failure may be imparted by deeper lithospheric structures.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413451

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