[S-CG45] Science of slow-to-fast earthquakes

[SCG45-40] Insights from Distributed Acoustic Sensing (DAS) Imaging of Submarine Faults in the Marmara Sea

*JI ZHANG¹, Aitaro Kato¹, Ahmet Anil Dindar², Wei Wang^3,4, Shigeki Nakagawa¹, Yosuke Aoki¹, Masanao Shinohara¹, Yoshiyuki Kaneda⁵ (1.Earthquake Research Institute, the University of Tokyo, 2.MARTEST Research and Training Center, Gebze Technical University, 3.Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences; Beijing, 100029, China., 4.College of Earth and Planetary Sciences, University of Chinese Academy of Sciences; Beijing, 100049, China., 5.Kagawa University)

Keywords:Distributed Acoustic Sensing, Submarine Faults, Ambient Noise Interferometry

The Marmara Sea hosts a critical segment of the North Anatolian Fault (NAF), where complex fault interactions play a key role in seismic hazard and earthquake dynamics. Understanding fault segmentation, velocity structure, and the transition between locked and creeping behaviors is essential for assessing stress accumulation and release processes in this tectonically active region. Distributed Acoustic Sensing (DAS) is an innovative technology that transforms existing fiber-optic cables into dense seismic arrays, enabling high-resolution monitoring of acoustic and seismic signals. In this study, we utilize a dark fiber optic cable deployed along Izmit Bay, crossing the NAF, to interrogate the seabed environment using DAS. This setup allows us to capture both passive seismic signals and ambient noise, providing unprecedented imaging of submarine fault structures and sedimentary layers. We analyze seven days of continuous DAS recordings using slant-stacking techniques to extract Scholte-wave dispersion curves, which we then invert to construct a high-resolution 2-D shear-wave velocity model. Additionally, we apply autocorrelation and natural migration methods to further delineate fault structures and lateral discontinuities along the cable. By comparing active seismic records with ambient noise cross-correlation results, we gain valuable insights into the distribution of subsurface sediments and fault geometry. Our findings reveal, for the first time, that ocean-bottom DAS in the Marmara Sea's faulted and basin environments can produce detailed images of submarine faults and detect potential zones of stress accumulation. Notably, ambient noise tomography, natural migration, and autocorrelation imaging indicate that the boundary of the Princes’ Islands (PI) fault segment remains active, while the main PI zone appears to be creeping and relatively aseismic. These results provide crucial evidence of varying fault behavior along the NAF, shedding light on the transition between locked and creeping segments. This study highlights the potential of ocean-bottom DAS as a powerful tool for seismic imaging and long-term monitoring of submarine fault systems. The ability to resolve fine-scale fault structures and track seismic coupling in real time opens new avenues for understanding rupture dynamics and earthquake hazards in complex marine environments.