Anatomy of the North Anatolian fault zone in the Marmara Sea, Western Turkey: Extensional basins above a continental transform

Abstract

Although it straddles an area of extreme earthquake risk, the origin of the Marmara Sea transtensional basin has been enigmatic. Recently acquired high-resolution seismic profiles and earthquake hypocenter locations show the crustal architecture to be characterized by a negative flower structure, bounded by two west-trending sidewall faults that are linked to a single vertical to steeply south-dipping master fault that extends to depths of >30 km. The negative flower structure has a complicated architecture consisting of relatively intact detached basinal blocks, separated by southwest-trending ridges which serve as strike-slip transfer zones between the basins. The basins and ridges are rotating counterclockwise, accommodated by the southward retreat of the southern sidewall of the flower structure as crustal material is passed from its eastern to western end along the transtensional strike-slip zone. This new interpretation provides a better context for understanding seismicity in the region and for understanding complexities of fault segmentation in large transtensional basins along continental transforms in zones of tectonic escape.