Scientists have made the first three-dimensional image of the North Anatolian fault beneath the Marmara Sea. This area lies close to Istanbul and has not seen a major earthquake in over 200 years. The study used electromagnetic signals recorded on land and below the sea. These signals measure how electricity flows through rocks, helping map the fault in detail. Turkey sits where several big tectonic plates meet. The North Anatolian fault stretches 1,500 km across the country and has caused many strong earthquakes. Since a deadly quake in 1939, big ruptures have moved west along the fault. The Marmara Sea part of the fault is hard to study because there are few instruments on the seafloor and standard methods don’t work well offshore. By using data from over 20 stations around the sea, researchers found zones of different rock strength and fluid content. Areas with low electrical resistivity have more fluids and are weaker. These spots usually have small earthquakes, which means stress is released slowly. High resistivity zones are stronger and locked, so stress builds there over time. The study shows that the borders between weak and strong zones are important. These boundaries could start big earthquakes. Instead of one risky spot, the fault has segments that behave differently. While the research does not predict exactly when the next quake will happen, it offers a clearer picture of how the fault works under the sea. This will help improve earthquake risk assessments and safety planning near Istanbul, a city facing serious seismic threats.