The Effect of the 3‐D Structure on Strain Accumulation and the Interseismic Behavior Along the North Anatolian Fault in the Sea of Marmara

Abstract

The 150‐km seismic gap in the Sea of Marmara is the longest section of the North Anatolian Fault that has not ruptured in the last century. Recent geodetic studies suggest that the interseismic coupling along the Main Marmara Fault (MMF) is heterogeneous with locked and creeping segments. Alternatively, the MMF is fully locked, but the strain is localized asymmetrically around the fault due to the deep basins. In this study, we build a 3‐D model of the region, including the basins and the 3‐D fault geometry, to study the competing effects of deep basins and the interseismic locking distribution using the observed Global Navigation Satellite System velocities. We conclude that the basins along the fault localize the interseismic strain, leading to slightly deeper‐estimated locking depths. The on‐land data are too far to constrain the full interseismic coupling, especially in the Central Marmara. The Western Marmara is better resolved, where we infer a ∼50‐km creeping zone. The transition from the creeping to the locked behavior in Western Marmara is around the Ganos Bend. The creeping zone correlates well with a higher rate of diffuse seismicity and repeating earthquakes, implying that the seismicity could be an indicator of interseismic behavior. Variations of earthquake focal mechanisms and associated regional stresses are also consistent with compressional and dilatational quadrants due to the creeping segment. The significant thrust components observed in the 2019 Silivri earthquake sequence north of the MMF can also be explained by the compressional loading due to the interseismic creep further west.

Variation of Fault Creep Along the Overdue Istanbul‐Marmara Seismic Gap in NW Türkiye

“…Comparable repeater depths are also found in the Kumburgaz Basin. This agrees with locking depths suggested by geodetic modeling for the Tekirdağ Basin and the MMF segment east of 28.5°E (Yılmaz et al, 2022). In the interval 27.7°E−28.1°E along the MMF our results suggest the absence of plate locking at shallow depths in agreement with offshore geodetic studies (Yamamoto et al, 2019).…”