Updated lithospheric 3D model(s) of the Sea of Marmara: thermal and rheological characteristics of the Main Marmara Fault – a segment of the North Anatolian Fault

The active strike slip North Anatolian Fault poses significant seismic hazard in Turkey. One of its parts - the Main Marmara Fault - extends across the northern Sea of Marmara close to the metropolitan area of Istanbul, where a potentially hazardous earthquake 7 is overdue according to paleoseismic statistics. At the same time the Main Marmara Fault exhibits a segmentation along‐strike with creeping and locked parts, the understanding of which is still a challenge. To address this challenge the GONAF observatory was initiated by ICDP and enabled continuous research in the recent years. We present results obtained in the frame of the DFG-ICDP priority program that include a new 3D lithospheric‐scale model of the Sea of Marmara that combines gravity modelling and seismic tomography analysis with thermal and rheological modelling. Using forward and inverse gravity modelling with free‐air gravity data and available constraints of geological units we derived the intra‐crustal density structure. Shear‐wave velocity tomography models provided insights into the temperature and density configuration of the uppermost mantle, and the geometry of the 1330°C isotherm. We find crustal density variations with a lower‐density crust over the western and creeping part of the Main Marmara Fault, and a denser crust below the Istanbul Zone where the Main Marmara Fault is supposed to be locked. We analysed the combined effects of the density structure and of the thermal field on the rheological configuration and discuss which implications this configuration may have for the deformation of the Main Marmara Fault.