Recent studies suggest that high pore pressures have caused seafloor creep-like deformation and slope failure in the Marmara Sea (e.g. Shillington et al., 2012). Stratigraphic analysis provides evidence for creep-like deformation in Marmara Sea sediments, however, no detailed quantitative geophysical analysis has been conducted to determine whether elevated fluid pressures exist in the Marmara Sea sediments today, or if these sediments are potentially near-critically stressed. If fluid pressures are high and the sediments are close to failure, only minor ground accelerations from earthquakes along the active Northern Anatolian Fault might trigger failure. For this study, I use high resolution multichannel 2D seismic data collected in the Marmara Sea to estimate indirectly P-wave and S-wave velocities that I then use to detect both possible gas accumulations and zones of high pore pressure. Specifically, I integrate interval P-wave velocities (using Dix equation), rock physics models, and Amplitude Versus Offset (AVO) methods to estimate Vs velocities. With Vp and Vs constrained, I then estimate where elevated fluid pressures in shallow (<500 >mbsf) sediment might exist in sediments on the southern margin of the Marmara Sea where pressure-driven creep-like deformation is hypothesized. I first characterize using forward models what normal versus overpressured AVO and Vp/Vs response should be like in the environment. Then, I compare model predictions with observations in a zone where creep-like deformation exists. The final product provides evidence for both if and where elevated pore pressure likely exists along the zone of noted sediment creep. I conclude by noting how sediment mineralogy and sedimentation rates likely play an important role in characterizing pore pressure evolution along this margin.
Matthew J. Hornbach
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Bolat, Rahmi M., "Explaining Creep-Like Deformation in the Marmara Sea: Results from AVO-Derived Vp/Vs and Pore Pressure Analysis" (2017). Earth Sciences Theses and Dissertations. 1.