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Turkey seismic activity & Marmara Sea fault movement

Updated 13 times since CLSTR started tracking revisions of this situation.

What changed

2026-09-13 13:17 UTC → 2026-09-16 04:56 UTC · added ~~removed~~

Seismic monitoring in Turkey remained intense through August 2026. Following a 4.5 magnitude earthquake in Gaziantep on 9 August, activity intensified in the Marmara Sea near the Princes' Islands between 18 and 20 August. These tremors, ranging from 1.1 to 3.2 magnitude, occurred at depths of 7 to 17 kilometers. Scientific assessments of the Marmara activity remain divided. Prof. Dr. Şener Üşümezsoy and Prof. Dr. Okan Tüysüz suggested the tremors involve secondary or tertiary fault segments, such as the Adalar fault, which they believe are unlikely to trigger a major event. Conversely, Prof. Dr. Osman Bektaş proposed the activity might indicate a “creep” phenomenon. Adding to this, Associate Professor Bülent Özmen warned that the activity confirms the Adalar fault is active, suggesting the probability of a magnitude 7 or greater earthquake is increasing. New underwater acoustic data presented at EGU 2026 revealed that a fault segment west of the Kumburgaz Basin is experiencing a slow creep of approximately 15 millimeters per year. Prof. Dr. Bektaş noted that an 8-kilometer-thick layer of soft sediment might be damping this movement, potentially masking higher speeds at greater depths. While this creep might release some accumulated seismic moment, experts warn a future earthquake could still reach a magnitude 6.0 or higher. By early September, Prof. Dr. Bektaş identified the Adalar-Çınarcık zone as a critical area for monitoring, noting that seismic migration along the North Anatolian Fault may pose a significant threat to Bursa rather than just Istanbul. ~~He cited eastward stress transfer and micro-earthquake clusters as key factors.~~ On 13 11 September, ~~small-scale tremors (magnitudes 1.0 to 2.1) were recorded in Kahramanmaraş, Adıyaman, Kütahya, Malatya, Balıkesir, Van,~~ reports highlighted widespread structural vulnerabilities, with the Chamber of Civil Engineers identifying approximately 6 million high-risk residences nationwide, particularly those built between 1980 and ~~Erzurum.~~ 2000. In Istanbul, scanning of 40,000 buildings revealed 18,800 constructed before 1999 carry high or very high risk, with 1,238 at risk of spontaneous collapse.

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