3-D electromagnetic imaging of highly deformed fluid-rich weak zones and locked section of the North Anatolian fault beneath the Marmara Sea

Abstract Reliable knowledge of the crustal properties beneath the North Anatolian fault (NAF), seismically silent for more than 250 years beneath the Marmara Sea (MS), is crucial for understanding seismic hazard and mitigating the potential for disaster on an enormous scale. In the present work, the first three-dimensional inverse modeling performed on a magnetotelluric dataset of the MS has unveiled localized weak and locked fault segments along this shear deformation zone. Low-resistivity regions along the northern branch of the NAF beneath the Central and Çınarcık-Imralı basins are likely attributed to the presence of fluids, which may represent a fault zone conductor in a fractured zone and can explain the densely populated microseismicity. These low-resistivity anomalies surrounded by higher resistivity structures imply that the segmented, multi-branched NAF system extends beneath the MS, following the Intra-Pontide suture zone. The resistive anomalies, between the Central and Çınarcık basins, along with those at the western and eastern extremities of the MS, presumably signify regions of stress accumulation, shedding light on the ongoing processes of fault mechanics at play in this critical region.