Transform Faults & the 2023 Iran (Khoy) Earthquake: Tectonic Context

Tectonic Setting of the January 2023 Khoy Earthquake

The Mw 5.9 earthquake on January 28, 2023, near Khoy, West Azerbaijan Province, Iran, occurred in a complex zone of continental collision and strike-slip faulting at the junction of three major plates.

Plate Configuration

• Arabian Plate moving north ~25 mm/yr.
• Eurasian Plate relatively stationary.
• Anatolian Plate escaping westward ~20 mm/yr.

Key Fault Systems

1. North Anatolian Fault (NAF): Right-lateral strike-slip. Extends from Karlıova (Turkey) eastward into Iran (becoming the North Tabriz Fault). Separates Eurasian & Anatolian plates.
2. East Anatolian Fault (EAF): Left-lateral strike-slip. Separates Anatolian & Arabian plates. Runs from Karlıova southwest to Mediterranean.
3. Bitlis-Zagros Suture/Collision Zone: Thrust faulting from Arabia-Eurasia convergence. Dominant south of Khoy.

Khoy's Position

Khoy lies in a transpressional zone between the NAF's eastern splays (North Tabriz, Salmas faults) and the Zagros thrust belt. The 2023 epicenter was near the Khoy Fault—a NW-SE striking, right-lateral strike-slip fault branching from the North Tabriz system.

Mechanism & Stress Interaction

• Focal Mechanism: Predominantly strike-slip with reverse component (transpression).
• Stress Transfer: 2023 Turkey earthquakes (Mw 7.8 & 7.5 on EAF/NAF) likely increased Coulomb stress on nearby Iranian faults, potentially advancing the Khoy rupture.
• Historical Precedent: 1930 Salmas (Mw 7.1), 2012 Ahar-Varzegan (Mw 6.4) on related structures.

Scientific Investigation Ongoing

Precise fault rupture mapping (InSAR, field surveys), aftershock relocation, and geodetic modeling are needed to confirm:

• Which specific fault segment ruptured.
• Slip distribution & depth.
• Static/dynamic triggering from Turkey quakes.
• Updated seismic hazard for Tabriz, Urmia, Khoy urban areas.

Broader Implication

The Iran-Turkey border region is a seismic gap with potential for Mw >7 events. The 2023 sequence underscores the need for cross-border seismic cooperation, resilient infrastructure, and updated building codes.