[S-SS04] Seismological advances in the ocean

[SSS04-10] Microseismic Activity and Fault Structure in the Eastern Marmara Sea: High-Resolution Observations from Ocean Bottom Seismometers (OBS)

*Nurcan Meral Ozel¹、Tugce Ergün¹、Yojiro Yamamoto ²、Narumi Takahashi ²、Ahmet Anil Dindar³、Remzi Polat¹、Fatih Turhan¹、Ceren Özer Sözdinler³、Yoshiyuki Kaneda ² (1.Bogazici University Kandilli Observatory and Earthquake Research Institute (KOERI), Istanbul, Turkiye、2.Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan、3.Gebze Technical University, Kocaeli, Türkiye)

キーワード：Ocean Bottom Seismometer (OBS), Microseismicity, North Anatolian Fault (NAF), Main Marmara Fault (MMF), Marmara Sea

The Main Marmara Fault (MMF), a key segment of the North Anatolian Fault (NAF), has remained unruptured since the 1999 Izmit (Mw 7.4) and Duzce (Mw 7.2) earthquakes, posing a major hazard to Istanbul. To enhance offshore seismic monitoring, we conducted a 10-month Ocean Bottom Seismometer (OBS) deployment from September 2023 to July 2024 in the eastern Marmara Sea, covering the Prens Adalari segment and Cinarcik Basin fault. Eight OBS units were deployed at depths of 145 to 1269 m with a 10-km spacing grid. Seven instruments recorded continuous data, detecting three times more microseismic events than land-based networks, with a minimum magnitude of ML 0.3. Preliminary results indicate that the Prens Adalari segment has a northwest-dipping fault plane, suggesting partial locking and strain accumulation. The southern Cinarcik fault shows persistent low-magnitude seismicity, indicating aseismic creep or episodic stress release. Hypocentral depths (5–20 km) and seismic clustering suggest cyclic activity variations influenced by stress redistribution and fluid migration. These findings provide crucial insights into fault segmentation, strain accumulation, and rupture dynamics. The improved microseismic resolution highlights the importance of OBS networks in complementing land-based seismic monitoring, especially for offshore active faults.