Upper crustal structure of the Marmara region, northwest Turkey from aeromagnetic anomalies: western segment of the North Anatolian Fault

This paper presents an investigation describing the potential future earthquake areas and the subsurface structures in the Marmara region (NW Turkey) by using aeromagnetic data. The region locates in the entrance of the North Anatolian Fault Zone (NAFZ) into the Marmara Sea and it has a crucial importance due to its seismological past. Firstly, the aeromagnetic dataset has been processed by using the power spectrum analysis. This analysis shows that the average depths of causative sources in the region range from 0.39 to 18.52 km. Secondly, to emphasize the magnetic anomalies caused by shallow sources, high-pass filter has been applied to the data. Finally, the Second vertical derivative method has been implemented to high-pass filtered data for delineating the exact location and trends of the subsurface structures. This final map clearly shows the boundaries of the causative sources. Anomalies align in the E-W direction from Izmit to Sapanca while the other anomalies located around Duzce elongate in the NE-SW direction. Moreover, the second vertical derivative map has shown that horsts in the region have no magnetization, and the magnetic anomalies become weak along the E-W direction in the north of the Central Ridge Horst. This can be associated with the existence of the horsts that are older than the magnetic material surrounding them. In addition, these horsts act as a barrier to the NAFZ and the NAFZ cannot pass through the region easily and the NAFZ has been separated into sub-branches towards the west in this region. As a result, this study provides valuable insights about the subsurface structures in the region and it plays a key role to define future earthquake areas.