East Anatolian Fault and Earthquake Insights

Eastern Turkey is one of the most seismically active regions in the world, with the East Anatolian Fault (EAF) playing a crucial role in its earthquake activity. This fault system has been responsible for numerous destructive earthquakes, making it an important subject of study for geologists and seismologists. Understanding its behavior can improve hazard assessments and preparedness efforts.

Tectonic Setting

The East Anatolian Fault (EAF) is a major left-lateral strike-slip fault that marks the boundary between the Anatolian and Arabian plates. It accommodates the westward movement of the Anatolian Plate as it is squeezed between the northward-moving Arabian Plate and the relatively stable Eurasian Plate. Unlike the North Anatolian Fault, which facilitates Anatolia’s motion toward the Aegean, the EAF absorbs compressional forces from the Arabia-Eurasia collision, shaping eastern Turkey’s seismic landscape.

The fault extends approximately 700 kilometers from the northeastern edge of the Dead Sea Fault Zone in southeastern Turkey to the Karlıova Triple Junction, where it meets the North Anatolian Fault. Along its length, the EAF is segmented, with individual strands accommodating varying degrees of slip. Geodetic measurements indicate an average slip rate of 6 to 10 millimeters per year—moderate compared to other major strike-slip faults like the San Andreas Fault. Despite this, accumulated strain over decades or centuries can lead to significant earthquakes.

The Arabian Plate moves northward at approximately 18 to 25 millimeters per year relative to Eurasia. This motion is unevenly distributed, leading to localized variations in strain accumulation and release. The interplay between strike-slip motion on the EAF and compressional forces from the broader collision zone creates a complex stress regime. Additionally, interactions with adjacent fault systems, including the Dead Sea Fault to the south and the North Anatolian Fault to the north, add to the region’s tectonic complexity.

Structural Segments

The EAF is not a continuous structure but a system of multiple segments, each with distinct geometric and kinematic characteristics. These divisions influence how stress accumulates and is released, shaping seismic behavior. Some segments experience frequent earthquakes, while others remain locked for extended periods, accumulating strain that may eventually trigger large events.

The Pütürge, Erkenek, and Pazarcık segments are particularly significant. The Pütürge segment was the source of the 2020 Elazığ earthquake (Mw 6.8), highlighting how long-dormant sections can suddenly rupture. The Erkenek segment remains a concern due to its prolonged lack of major seismic activity, suggesting critical stress accumulation. The Pazarcık segment played a role in the 2023 Kahramanmaraş earthquake sequence, which involved multi-segment ruptures.

Segment boundaries often coincide with geometric irregularities such as stepovers, bends, or secondary fault branches, which can either inhibit or facilitate rupture propagation. Releasing bends lead to localized extensional deformation, forming pull-apart basins, while restraining bends introduce compressional forces, increasing the likelihood of locked sections. These structural features influence rupture scenarios and seismic hazard distribution.

Surface Expressions

The EAF is visible at the surface through fault scarps, linear valleys, offset river channels, and pressure ridges. These features document the fault’s activity and long-term deformation patterns. Over time, displacement has created geomorphic markers that illustrate past seismic events and signal future rupture behavior.

One of the most notable surface expressions is the lateral displacement of waterways. The Euphrates River and its tributaries show clear deflections where they intersect the fault, indicating sustained tectonic movement. These offsets help estimate cumulative slip rates and reconstruct seismic history. Sag ponds, formed in transtensional sections, preserve sedimentary records of past earthquakes, offering insights into recurrence intervals.

Deformation varies along the fault, influenced by local geometry and lithology. Compressional forces create pressure ridges, marking zones of localized crustal shortening, while extensional segments produce pull-apart basins. These contrasting landforms provide important clues about underlying seismic processes.

Seismic Characteristics

The EAF exhibits irregular seismic cycles, with periods of quiescence followed by clusters of significant earthquakes. Some sections slip aseismically, while others remain locked, accumulating strain until a major rupture occurs. The fault’s left-lateral strike-slip motion produces predominantly horizontal displacement, but localized oblique slip contributes to variations in rupture mechanics.

Seismic moment release has been uneven, with certain segments producing large earthquakes while others remain relatively quiet. The 2020 Elazığ earthquake (Mw 6.8) struck a section that had not ruptured in over a century, demonstrating the unpredictable nature of strain accumulation. The 2023 Kahramanmaraş earthquake sequence showed how multiple segments can rupture in succession, amplifying energy release and extending shaking over broader areas.

Local Stress Fields

Stress distribution along the EAF is heterogeneous, shaped by regional tectonic forces and local geological conditions. The primary driver is the northward movement of the Arabian Plate, but variations in lithology, fault geometry, and rupture history create localized stress concentrations. Some sections release stress through aseismic slip, while others remain locked, posing a greater seismic hazard.

Stress transfer between fault segments also influences earthquake sequences. When one section ruptures, it redistributes stress to neighboring areas, potentially triggering subsequent events. This was evident in the 2023 Kahramanmaraş earthquake sequence, where initial ruptures altered stress conditions on adjacent segments. Secondary faults in the region further complicate rupture dynamics, sometimes leading to multi-fault events. Advanced modeling techniques, such as Coulomb stress analysis, help predict how stress redistribution may influence future seismic activity.

Adjacent Fault Connections

The EAF is part of a broader fault network that accommodates regional tectonic forces. Its most significant connection is with the North Anatolian Fault (NAF) at the Karlıova Triple Junction, where strain is distributed among multiple fault strands. Historical earthquake sequences suggest stress transfer between the EAF and NAF can influence rupture timing.

To the south, the EAF intersects with the Dead Sea Fault, which accommodates motion between the Arabian and African plates. Stress redistribution between these faults contributes to seismic activity in southeastern Turkey and the Levant. Numerous secondary faults branch from the EAF, some exhibiting strike-slip motion similar to the main fault, while others accommodate localized extensional or compressional forces. These subsidiary structures can act as rupture pathways, sometimes allowing seismic energy to propagate beyond the primary fault. Understanding these interactions is essential for refining seismic hazard models, as multi-fault ruptures can generate larger and more destructive earthquakes.