[J07-3] Tracking the sea floor in motion III

[J07-3-06] Slip rate of the North Anatolian Fault at the western part of the Sea of Marmara through seafloor geodetic measurement for two years

^○Ryusuke Yamamoto¹, Motoyuki Kido², Yusaku Ohta¹, Narumi Takahashi³, Yojiro Yamamoto⁴, Dogan Kalafat⁵, Ali Pinar⁵, Haluk Ozener⁵, Sinan Ozeren⁶, Yoshiyuki Kaneda⁷ (1.Graduate School of Science, Tohoku University, Sendai, Japan, 2.International Research Institute of Disaster Science, Tohoku University, Sendai, Japan, 3.National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan, 4.Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan, 5.Kandilli Observatory and Earthquake Research Institute, Bogazici University, Istanbul, Turkey, 6.Istanbul Technical University, Istanbul, Turkey, 7.Institute of Education, Research and Regional Cooperation for Crisis Management Shikoku ,Kagawa University, Takamatsu, Japan)

The North Anatolian Fault (NAF) regionally has right-lateral block motion (~25 mm/yr) but local slip rate along the fault varies from place to place, which may control the inter-seismic stress accumulation. Rupture area along NAF is known to migrate roughly from east to west in the last century. The Marmara segment is known as seismic gap since 1766 (Marmara earthquake) or 1912 (Ganos earthquake / Murefte-Sarkoy earthquake), while the Izmit and Duzce earthquakes just east of the Marmara segment occurred in 1999. Thus, we investigate slip rate of NAF in the Sea of Marmara using seafloor acoustic extensometers, where on-shore geodetic observations (e.g. GNSS or InSAR) cannot be accessible.
In 2014, we installed four instruments at the Western High, where the Marmara main fault can be clearly identified, and added one more instrument in 2015. Since then, we recovered almost two years of continuous ranging data and evaluated the creep rate at this site as 10 +/- 5 mm/yr, which corresponds nearly a half coupling rate to the regional block motion. Using this constraint and surrounding onshore GNSS data, we constructed a simple fault model, that has partial creep layer from the seafloor to some 10-30 km depth and full creep below. We have installed two additional GNSS site in the Sea of Marmara since 2016 in order to constrain depth extent of the partial creep layer, which may be discussed with the seismicity distribution obtained by ongoing OBS surveys.
Acknowledgement: This observation is carried out in the MarDiM (Marmara Disaster Mitigation) project, SATREPS promoted by JICA, JST and Ministry of Development of Turkey