S21G-3493: Utilizing Distributed Acoustic Sensing (DAS) for Submarine Fault Analysis in the Marmara Sea

Distributed Acoustic Sensing (DAS) is a cutting-edge method that allows for high-resolution monitoring of acoustic signals along fiber-optic cables, providing detailed insights into seismic activities and fault dynamics beneath the seabed. We utilized DAS technology with dark fiber optic cables under the Marmara Sea to analyze seismic activity and faults in the area. The fiber optic cable spans 27 km, with 10 km on land and 17 km underwater, crossing two submarine faults. We recorded 28 days of DAS data from May 20 to June 16, 2024. Using the catalog provided by the Disaster and Emergency Management Authority (AFAD), we tested DAS's monitoring capability, successfully detecting small nearby earthquakes, including a 1.4 ML event 16 km from the cable. Based on these observations, we mapped the underwater cable distribution. The seismic records enabled us to infer information about underwater topography and fault distribution. Using scattered waveforms from teleseismic data, we conducted a preliminary characterization of the submarine fault structure. Due to the coupling between the cable and the faults and the weak energy of teleseismic events, effective information was not recorded near some faults, indirectly confirming their existence. DAS likes a dense array of stations, allowing us to utilize both passive seismic signals and ambient noise techniques. By applying cross-correlation and autocorrelation methods, we characterized the underwater velocity layers and structures. Comparing the seismic records with the cross-correlation results, we observed the distribution of underwater sediments and faults. Additionally, we used the OpenSWPC program for forward modeling to explain the observed scattering and different travel time phenomena. As a new detection method, DAS has significant implications for understanding the region's geophysical characteristics and improving earthquake preparedness by closely analyzing the behavior of submarine faults.