Deformation styles and rates along the North Anatolian Fault zone in the sea of Marmara based onshore-offshore seismic, geodetic and geologic data

Abstract

The aim of the thesis is to make a contribution on the long lasting debate on complex fault geometry along the northern branch of the NAF beneath the Sea of Marmara, using seismological, geodetic and geologic data. The focal mechanisms of: (1) small to moderate size events are obtained by CMT inversion technique of Kuge (2003), using onshore waveform data from 2002-2015, (2) micro-earthquakes are obtained using technique of Horiuchi (2015), using offshore waveform data recorded by 15 OBS stations from 2015-2016. The geodetic horizontal crustal strain rates are determined at equally spaced grid points by interpolating northing and easting components of the 112 GPS vectors from 1994-2013. The strain ε̇ and moment rates Ṁ are calculated by Kostrov’s (1974) summation method later modified by Ward (1994). The results indicate that extensional and strike-slip style dominates the region, while compression features are rare. Significant elongation is observed in Çınarcık Basin (CB) and the area between Marmara Island and Central Basin (CeB). Compressional or transpressional features is derived to the west of Marmara Island and Ganos and in the Central segment extending from CeB toward CB. The sparse seismicity beneath the Kumburgaz Basin yields the lowest ε̇ estimated in the region, 11x10-8 /y, supporting the idea that this section could be locked and accumulating strain. The Ṁ estimation results for each segment show that Ṁseis, calculated for instrumental period, are greatly lower than Ṁgeod and Ṁgeol. This feature can be interpreted in two ways: (1) action of aseismic strain release (creeping), (2) strain accumulation along fault segments is underway and only small portion of the accumulated seismic energy is released by small magnitude events. ε̇geod results point out the highest values, 24x10-8 /y, in CB, while the lowest values, 11x10-8 /y, are observed in Central Marmara. The highest ε̇ in both edges of the fault segment in CB can be indicative of steadily creeping fault segment. Vice versa lower strain rates in Central Marmara region suggest that this segment of NAF is locked.