3-D seismic delineation of the North Anatolian Fault System shear zone in the Western Half of Marmara Basin, Türkiye

Abstract

We performed a 3-D AI-based structural interpretation of a seismic image volume derived from 3-D prestack time migration, and delineated fault geometries and the subsidiary Riedel shear fractures within the sedimentary overburden associated with the North Anatolian Fault System (NAFS) in the western half of Marmara Basin, Türkiye. We thus inferred existence of dextral strike-slip basement fault segments with extensional (releasing) and contractional (restraining) stepovers that gave rise to the formation of the geomorphic features --- the pull-apart Tekirdağ and Central Basins, and the Western High pop-up structure, respectively. The NAFS shear zone within the study area extends E-W and has a 20-km maximum N-S width. Previous investigations based on 3-D inversion of gravity data over the Sea of Marmara and the surrounding region, and long-range E-W seismic refraction profiling across the basin infer that the Moho depth is as shallow as 24 km in the western half of Marmara Basin --- nearly 6 km shallower than the average regional depth of 30 km. The Moho uplift forms a fairly narrow ridge (<30 km) confined to the NAFS shear zone, coincident with the E-W principal strike direction of the NAFS. This implies that it may have been formed contemporaneously with the formation of the pull-apart basins which gave rise to crustal stretching within the stepovers, resulting in basin subsidence, crustal thinning, and Moho uplift. The segmentation in the NAFS and the E-W trending Moho ridge may have led to the formation of earthquake rupture barriers and weak zones in the brittle upper crust.