Abstract Beneath the Marmara Sea, Turkey, the Main Marmara Fault (MMF), the offshore part of the North Anatolian Fault (NAF), is a well-known seismic gap for future M > 7 earthquakes. However, its detailed fault geometry and microearthquake activity have been debated for several decades. Using data acquired from long-term ocean bottom seismograph (OBS) observations, we made precise hypocenter estimations based on 3-D Vp and Vs velocity structures and assessed the fault geometry beneath the western and central parts of the MMF. The results indicate a segmentation boundary between the near-vertical western part and the south-dipping eastern part located around 28.10°E. Enriched OBS locations indicate microseismicity along both the inner and outer boundary faults of the Central Basin, especially on the western side. A comparison with previously published results suggests that the seismicity pattern has not changed for at least two years, between 2014 and 2016. Using a combined dataset of this and previous studies, lateral variations in the dip angle along the MMF fault segment from 27.4°E to 28.8°E were investigated. Based on this, we depicted on-fault seismicity along the MMF and defined three inactive areas of microseismicity. Two are located in the western segment, corresponding to the rupture area of the 1912 Ms. 7.4 earthquake, and the other, the largest, is located on the eastern segment. From a comparison of previous seismic and geodetic studies, it is considered that this area is a fully locked zone and has the potential for large earthquakes. Having compared the difference between hypocenter locations determined from OBSs and land-based stations, it is proposed that the epicentral locations of the mainshock and aftershocks of the September 26, 2019, M 5.7 earthquake are located much closer to the MMF than locations reported from only land-based results.

中文翻译：

---

土耳其马尔马拉海西部和中部下方断层几何，基于海底地震观测：对未来大地震的影响

摘要 在土耳其马尔马拉海之下，北安纳托利亚断层 (NAF) 的近海部分马尔马拉主断层 (MMF) 是众所周知的未来 M > 7 地震的地震间隙。然而，其详细的断层几何形状和微地震活动已经争论了几十年。使用从长期海底地震仪 (OBS) 观测获得的数据，我们根据 3-D Vp 和 Vs 速度结构进行了精确的震源估计，并评估了 MMF 西部和中部下方的断层几何形状。结果表明，近垂直的西部和南倾的东部之间的分割边界位于 28.10°E 附近。丰富的 OBS 位置表明中央盆地内外边界断层都有微地震，特别是在西侧。与先前发表的结果进行比较表明，地震活动模式在 2014 年至 2016 年之间至少有两年没有改变。使用本研究和先前研究的组合数据集，从 27.4°E 沿 MMF 断层段的倾角横向变化到 28.8°E 进行了研究。在此基础上，我们描绘了沿 MMF 的断层地震活动，并定义了三个不活跃的微地震活动区。两个位于西段，对应 1912 年 7.4 级地震的破裂区，另一个最大的位于东段。对比以往的地震和大地测量研究，认为该地区是一个完全锁定的地带，具有发生大地震的潜力。比较了由 OBS 和陆基台站确定的震源位置之间的差异，