NH13D-1956
Long term seismic observation using ocean bottom seismographs in Marmara Sea, Turkey

Monday, 14 December 2015
Poster Hall (Moscone South)
Narumi Takahashi1, Ali Pinar2, Dogan Kalafat2, Yojiro Yamamoto3, Seckin Citak3, Mustafa Comoglu2, Özkan Çok2, Zafer Ogutcu2, Murat Suvarikli2, Suleyman Tunc2, Cemil Gurbuz2, Nurcan Ozel2 and YoshiYuki Kaneda4, (1)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan, (2)Bogazici Univ.KOERI, İstanbul, Turkey, (3)JAMSTEC, Yokohama, Japan, (4)Nagoya University, Disaster mitigation center, Nagoya, Japan
Abstract:
The North Anatolian Fault crosses the Marmara Sea with a direction of E-W. There are many large earthquakes repeatedly along the fault with a linkage each other. Due to recent large eastern Aegean earthquake with M6, the Marmara Sea is the “blank zone”. Japan and Turkey have a SATREPS collaborative study to clarify the structural characters, construct fault models, simulate the strong motion and tsunami, evaluate these risks with hazard maps and educate disaster prevention for local governments and residents. Our activity is one of the most basic studies, and the objectives are to clarify hypocenter locations, monitor the move, and construct fault models referring seismic/magnetotelluric structures, geodetic nature and trenching works. The target area is from western Marmara Sea to the off Istanbul area along the north Anatolian Fault.

We deployed ten Ocean Bottom Seismographs (OBSs) between the Tekirdag Basin and the Central Basin in September, 2014. Then, we added five Japanese OBSs and deployed them at the western end of the Marmara Sea and the eastern Central Basin to extend observed area in March, 2015. The OBS has a three-component velocity sensor with a natural frequency of 4.5 Hz and a hydrophone. Japanese team have clarified seismicity around Japan using the OBS. The magnitude of the detected events is 1.0-1.5. We retrieved all 15 OBSs in July, 2015 and deployed them again on the same locations after data copy and battery maintenance.

We started OBS data analysis combined with land stations data. Now we detect events automatically using these data and succeeded detection of over one thousand around the north Anatolian Fault. The tentative results show heterogeneous seismicity. The western and central basins have relative high seismicity and the seismogenic zone becomes thicker rather than previous estimation. Then we will evaluate hypocenter locations with high resolution and discuss the shape of faults in each segment and their linkage.

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