|Title||Detailed spatial distribution of microearthquakes beneath the Marmara Sea, Turkey, deduced from long-term ocean bottom observation|
|Publication Type||Conference Proceedings|
|Year of Conference||2016|
|Authors||Yamamoto, Y, Takahashi, N, Pınar, A, Kalafat, D, Citak, S, Comoglu, M, Polat, R, Cok, O, Ogutcu, Z, Suvarikli, M, Tunc, S, Gurbuz, C, Turhan, F, Ozel, N, Kaneda, Y|
|Conference Name||European Geophysical Union General Assembly|
The North Anatolian Fault (NAF) crosses the Marmara Sea in E-W direction, accommodating about 25 mm/yr of right-lateral motion between Anatolia and the Eurasian plate. There are many large earthquakes along the 1500 km long NAF repeatedly occurred and interacted each other. The recent large northern Aegean earthquake with Mw=6.9 filled one of the last two seismic gaps on NAF that experienced extraordinary seismic moment release cycle during the last century and confirmed a remained blank zone in the Marmara Sea. However, this segment keeps its mystery due to its underwater location. Earthquake hazard and disaster mitigation studies in Marmara region are sensitive to detailed information on fault geometry and its stick-slip behavior beneath the western Marmara Sea. We have started ocean bottom seismographic observations to obtain the detailed information about fault geometry and its stick-slip behavior beneath the western Marmara Sea, as a part of the SATREPS collaborative project between Japan and Turkey namely “Earthquake and Tsunami Disaster Mitigation in the Marmara Region and Disaster Education in Turkey”. The target area spans from western Marmara Sea to offshore Istanbul along the NAF. In the beginning of the project, we deployed ten Ocean Bottom Seismographs (OBSs) between the Tekirdag Basin and the Central Basin (CB) in September 2014. Then, we added five Japanese OBSs and deployed them in the western end of the Marmara Sea and in the eastern CB to extend the observed area in March 2015. We retrieved all 15 OBSs in July 2015 and deployed them again in the same locations after data retrieve and battery maintenance. From continuous OBS records, we could detect more than 700 events near the seafloor trace of NAF during 10 months observation period whereas land-seismic network could detect less than 200 events. We estimated the micro-earthquake location using manual-picking arrival times incorporating station corrections. The tentative results show heterogeneous seismicity. The Western High (WH) and CB have relative high seismicity and the seismogenic zone was found to be thicker than the previous estimations done by other researchers. Our result clearly shows that the maximum depth of seismogenic zone is about 24 km beneath the WH and the western half of CB. This depth suddenly decrease to about 15 km in the eastern half of CB, suggesting that there is some structural or frictional boundary on NAF around 28E. Our results also suggested that the dip angle of NAF is almost vertical beneath WH, whereas it is about 10 degrees southward dipping beneath the eastern CB.We will perform local seismic tomography to obtain more precious hypocenter location and fault geometry.