Petersen, Florian (2016) Acoustic Seafloor Geodesy: Strain measurement across the North Anatolian Fault in the Sea of Marmara. (Master thesis), Christian-Albrechts-Universität, Kiel, V, 77 pp.

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Abstract

Over 70 % of Earth’s surface is covered by water and inaccessible to standard methods of satellite geodesy. The emerging field of seafloor geodesy aims to provide methods to resolve seafloor deformation with high accuracy. In this thesis data from the first GEOMAR Helmholtz Centre for Ocean Research Kiel acoustic network deployment across the North Anatolian Fault in the Sea of Marmara will be analyzed and discussed. The dextral strike-slip fault system has produced a series of large devastating earthquakes over the last century such as the Izmit (Mw 7.6) earthquake in 1999. However, the Istanbul-Silivri fault segment in the Marmara Sea has not ruptured since 1766 and remains in the interseismic phase. The acoustic seafloor geodetic network is designed to measure strain between transponders on the seafloor. The network consists of six autonomous transponders installed on the seafloor and measures sound velocity, tilt, temperature, pressure and time of flight between the transponders.

The sound speed sensors show a long term drift resulting in apparent o sets in baselines. Therefore, an approach is developed which uses constant salinity values for the estimation of sound speed. The resolution of a baseline measurements is defined as the standard deviation over time and increases linearly to ranging distance up to 1 km. Synthetic baselines are estimated in order to compare the di erence of baselines calculated using a water column of constant sound velocity gradient with the measured data including spatial heterogeneity along the ray path. About 65 % of the baseline fluctuations are suggested to originate from spatial heterogeneity along the ray path.

Time series of 18 months reveal the absence of deformation estimates beneath the geodetic array within the resolution of 5 mm/a. The slip estimate from far field geodetic land stations as well as the absence of deformation from the acoustic geodetic seafloor data indicate that the North Anatolian Fault is highly locked and accumulating strain. The single baseline located in the nework’s west is showing deformation at a rate of 7 mm/a corresponding to the movement of a potential normal fault imaged by AUV Bathymetry.

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