ŞÜKRÜ ERSOY, ÖZCAN ERDOĞAN, FİLİZ KATMAN, SERHAT YILMAZ (9731) İNSANOĞLUNU BEKLEYEN TEHLİKELER HAZARDS FOR HUMANKIND REZA SABER, VEYSEL IŞIK, AYŞE ÇAĞLAYAN (9897) ARAS FAY ZONU BOYUNCA (KB İRAN) MORFOMETRİK VE INSAR VERİ ANALİZİYLE DOĞAL AFET RİSKLERİNİN BELİRLENMESİ DETERMİNATİON OF NATURAL DİSASTER RİSKS ALONG ARAS FAULT ZONE (NW IRAN) USİNG MORPHOMETRİC AND INSAR DATA ANALYSİS EFNAN ŞORA GÜNAL, UĞUR GÜREL (9907) YERALTI MADENLERİNDE SİSMİK AKTİVİTELERİN TAHMİNİ İÇİN ÖZNİTELİKLERİN ANALİZİ ANALYSİS OF FEATURES FOR PREDİCTİON OF SEİSMİC ACTİVİTİES İN UNDERGROUND MİNES ŞENER CERYAN (9959) ALTINOLUK-GÜRE (BALIKESİR) YERLEŞİM ALANININ SIVILAŞMA ŞİDETİ VE FAYLARDAN UZAKLIĞIN BİRLİKTE KULLANILARAK MİKRO-BÖLGELENDİRİLMESİ THE MİCROZONATİON OF THE SETTLEMENT AREA OF ALTINOLUK-GÜRE (BALIKESİR) USİNG THE LİQUEFACTİON SEVERİTY INDEX AND DİSTANCE FROM FAULTS TOGETHER CHAIRMAN/OTURUM BAŞKANI: ŞÜKRÜ ERSOY 26.06.2019 ÇARŞAMBA/WEDNESDAY 10:00 12:00

PreviousNext No AccessProceedings of the 13th SEGJ International Symposium, Tokyo, Japan, 12–14 November 2018Estimation of shallow S-wave velocity structure using microtremor exploration at strong motion stations observed the 2014 Aegean Sea earthquakeAuthors: Kosuke ChimotoHiroaki YamanakaSeckin Ozgur CitakOzlem KaragozOguz OzelHiroaki YamanakaKosuke ChimotoTokyo Institute of TechnologySearch for more papers by this author, Hiroaki YamanakaTokyo Institute of TechnologySearch for more papers by this author, Seckin Ozgur CitakÇanakkale Onsekiz Mart UniversitySearch for more papers by this author, Ozlem KaragozÇanakkale Onsekiz Mart UniversitySearch for more papers by this author, Oguz OzelIstanbul UniversitySearch for more papers by this author, and Hiroaki YamanakaTokyo Institute of TechnologySearch for more papers by this authorhttps://doi.org/10.1190/SEGJ2018-132.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract The 2014 Aegean Sea earthquake (Mw 6.9) occurred in the northern Aegean Sea on the border of Greece and Turkey on May 24. This event caused several damage to buildings in Greece and Turkey. The national strong motion network in Turkey observed strong motions during this event. To understand the effect of shallow soil amplification on strong motion records, we performed microtremor array exploration. We measured microtremors at the strong motion station in Gokceada Island, located close to the epicenter, Canakkale and Enez. The array with the size of about 30m to 2m was deployed at each site and measured microtremors about 15 minutes. The SPAC method was used to estimate dispersion curves of Rayleigh wave phase velocity. The dispersion curves were used to estimate S-wave velocity structure with the method of Hybrid Heuristic inversion by assuming 7 layers structure. The shallow S-wave velocity at Strong motion station in Gokceada Island was not lower than center of the city. Furthermore, the site where the building damage was observed has higher S-wave velocity. At Canakkale, where also had damage to buildings, the S-wave velocities are variable at three strong motion stations. It is quite low at seaside of Canakkale, while it is quite high at several hundred meters away from the coast. The S-wave velocity at Enez, where observed long period motion during the event was also low and cause large amplification to ground motion. Keywords: S-wave velocity structure, Microtremor array exploration, The 2014 Aegean Sea earthquake, GokceadaPermalink: https://doi.org/10.1190/SEGJ2018-132.1FiguresReferencesRelatedDetails Proceedings of the 13th SEGJ International Symposium, Tokyo, Japan, 12–14 November 2018ISSN (online):2159-6832Copyright: 2019 Pages: 588 publication data© 2018 Published in electronic format with permission by the Society of Exploration Geophysicists of JapanPublisher:Society of Exploration GeophysicistsSociety of Exploration Geophysicists of Japan HistoryPublished Online: 29 Apr 2019 CITATION INFORMATION Kosuke Chimoto, Hiroaki Yamanaka, Seckin Ozgur Citak, Ozlem Karagoz, Oguz Ozel, and Hiroaki Yamanaka, (2019), "Estimation of shallow S-wave velocity structure using microtremor exploration at strong motion stations observed the 2014 Aegean Sea earthquake," SEG Global Meeting Abstracts : 511-513. https://doi.org/10.1190/SEGJ2018-132.1 Plain-Language Summary KeywordsS-wave velocity structureMicrotremor array explorationThe 2014 Aegean Sea earthquakeGokceadaPDF DownloadLoading ...

To accurately estimate the coseismic rupture area in a Nankai megathrust earthquake and predict seismic and tsunami hazards, various three-dimensional models of the subducting plate geometry and simple seismic velocity models of the subduction zone in SW Japan have been proposed. However, to ensure consistency among studies, more realistic and reliable standard models must be developed. Here, we use wide-angle ocean-bottom seismographic survey results to develop models of the three-dimensional geometry of the subducting plate and of the three-dimensional P-wave velocity structure around the Nankai Trough. We confirmed the reliability of the proposed models by comparing theoretical first arrivals, calculated from two-dimensional structure models sampled from the three-dimensional model along seismic profile lines, with observed traveltime data. The proposed models are the first to be visible and to attempt to represent the actual seismic velocity structures around the entire Nankai Trough in SW Japan. Although the spatial validity of the three-dimensional velocity structure model could not be strictly evaluated, we confirmed that the differences between hypocenter parameters determined from previously published seismic tomography results and those obtained by using our three-dimensional structure model were sufficiently small (latitude and longitude within +/- 0.1 degrees and depth within approximately +/- 5 km). Therefore, our three-dimensional structure model is suitable for use as an initial model for hypocenter determination.

On 24 May 2014, a Mw 6.9 earthquake occurred in the west of Gokceada Island, northern Aegean Sea. The earthquake was close to Canakkale, Enez, Tekirdag cities, and damaged 300 buildings in the Marmara Region, NW Turkey. We simulated its broadband (0.1–10 Hz) ground motions including 1D deep and shallow structures soil amplification effects at the 12 strong ground motion stations in the western Marmara Region. The 1D deep velocity structures from the focal layer to the engineering bedrock with an S-wave velocity of 0.78 km/s in different azimuthal directions were tuned by comparing the observed group-velocity dispersion curves of Rayleigh and Love waves from the mainshock with theoretical ones. We also added the shallow parts from previous surveys into the 1D models. Synthetic seismograms on the engineering bedrock were generated using the discrete wave number method with a source model and the 1D deep velocity structures. Then the surface motion was generated considering shallow soil amplification. The synthetic seismograms are generally in good agreement with the observed low and high-frequency parts at most of the stations indicating an appropriateness of the source model and the 1D structural model.

Both the geometry and the depth of the seismogenic zone of the North Anatolian Fault under the Marmara Sea (the Main Marmara Fault (MMF)) are poorly understood, in part because of the fault's undersea location. We recorded 10months of microseismic data with a dense array of ocean bottom seismographs and then applied double-difference relocation and 3-D tomographic modeling to obtain precise hypocenters on the MMF beneath the central and western Marmara Sea. The hypocenters show distinct lateral changes along the MMF: (1) both the upper and lower crust beneath the Western High are seismically active and the maximum focal depth reaches 26km; (2) seismic events are confined to the upper crust beneath the region extending from the eastern part of the Central Basin to the Kumburgaz Basin; and (3) the magnitude and direction of dip of the main fault change under the Central Basin, where there is also an abrupt change in the depth of the lower limit of the seismogenic zone. We attribute this change to a segment boundary of the MMF. Our data show that the upper limit of the seismogenic zone corresponds to sedimentary basement. We also identified several seismically inactive regions within the upper crust along the MMF; their spatial extent beneath the Kumburgaz Basin is greater than beneath the Western High. From the comparison with seafloor extensometer data, we consider that these regions might indicate zones of strong coupling that are accumulating stress for release during future large earthquakes.

(1) JAMSTEC, CEAT FORECASTING, Yokohama, Japan, (2) Department of Geophysical Engineering, Istanbul University, Istanbul, Turkey, (3) Department of Environmental Science and Technology, Tokyo Institute of Technology, Tokyo, Japan, (4) Department of Geophysical Engineering, Canakkale Onsekiz Mart University, Canakkale, Turkey, (5) National Research Institute of Fire and Disaster, Tokyo, Japan, (6) Faculty of Civil Engineering, Department of Civil Engineering, Construction, Yıldız Technical University, Istanbul, Turkey, (7) Research Institute of Nuclear Engineering, Fukui University, Fukui, Japan, (8) Department of Earthquake Engineering, Kandilli Observatory and Earthquake Research Institute, Bogazici University, Istanbul, Turkey, (9) Earthquake Research Institute, University of Tokyo, Tokyo, Japan

関東平野を対象とした既往の数値解析手法のベンチマークテストでは、差分格子の間隔により後続表面波がチームにより異なるという問題点が指摘された。2013年度のベンチマークテストは2004年紀伊半島南東沖地震前震を用いて行われ、複数のモデルについて計算結果の比較検討を行った。差分格子を統一した均質・2層地盤モデルを用いたケースでは各チーム間で高い整合性が得られたが、モデル境界面からの反射波の処理の違いによる結果の差異が見られ、Q値の設定の違いが反射波に影響を与え、その設定方法に注意する必要があるという新たな課題が明らかになった。差分格子を統一せず、23層地盤モデルを用いたケースでは、差分格子の違いにより地盤構造の差異が生まれ、震源から遠方になるほど計算結果に影響を与えることが示唆された。

Rapid determinations of centroid moment tensor (CMT) of earthquakes, namely the source centroid location, focal mechanism, and magnitude is important for early disaster responses and issuing Tsunami warnings. Using the SWIFT system (Source pa-rameter determinations based on Waveform Inversion of Fourier Transformed seismograms) developed by Nakano et al. (2008), we are developing earthquake monitoring system in Turkey. Also determinations of CMT solutions for background seismicity would reveal the tectonics in the target region, which contribute to develop scenarios for future disastrous earthquakes. The North Anatolian fault (NAF) is one of most active fault in Turkey, which is a right-lateral fault system running in the East-West direction. NAF can be separated into a number of segments of which ruptures have propagated from east to west in the 20th century. The 1999 Izmit (Kocaeli) earthquake (Mw 7.4) is the westernmost activity along NAF in recent years, and next activity below the Sea of Marmara is anticipated. On 24 May 2014, an Mw 6.9 (USGS) earthquake occurred beneath the northern Aegean Sea, western extension of NAF. A seismic gap between these events still exists beneath the Sea of Marmara. Using data from broad-band seismometers (Guralp CMG-3T, CMG-3ESP, or CMG-3ESPC) of the regional network in Turkey, we determined CMT solutions of earthquakes along the NAF beneath the Sea of Marmara and Sea. Seismic events are selected from the USGS ANSS Comprehensive Catalog (ComCat) with magnitude larger than 4 in the target area. We analyzed earthquakes that occurred between 2008 and 2014. We selected seismograms with good data quality. The seismograms are corrected for the seismometer response, band-pass filtered between 20-50 s, and integrated in time to obtain displacement seismograms. The Green functions are synthesized assuming the standard Earth model ak135. Assuming a double-couple source, waveforms are inverted in the frequency domain to obtain best-fit source location and mechanism.

The faults’ geometry and their seismic activity beneath the Marmara Sea have been under debate for a couple of decades. We used data recorded by three ocean bottom seismographs (OBSs) over a period of 3 months in 2014 to investigate the relationship of fault geometry to microseismicity under the western Marmara Sea in Turkey. We detected a seismic swarm at 13 to 20 km depth beneath the main Marmara fault (MMF), and the maximum depth of seismogenic zone was 25 km within the OBS observation area. These results provided evidence that the dip of the MMF is almost vertical and that the seismogenic zone in this region extends into the lower crust. Our analysis of past seismicity indicated that the seismic swarm we recorded is the most recent of an episodic series of seismic activity with an average recurrence interval of 2–3 years. The repetitive seismicity indicates that the MMF beneath the western Marmara Sea is coupled and that some of the accumulated strain is released every 2 to 3 years. Our study shows that OBS data can provide useful information about seismicity along the MMF, but more extensive studies using more OBSs deployed over a wider area are needed to fully understand the fault geometry and stick–slip behavior of faults under the Marmara Sea.

We determined the centroid moment tensor (CMT) solutions of earthquakes that occurred along the North Anatolian fault (NAF) beneath the Sea of Marmara and the Aegean Sea, using data obtained from Turkey’s broad-band seismograph network. The CMT solution of the 2014 Aegean Sea earthquake (Mw 6.9) represents a strike-slip fault, consistent with the geometry of the NAF, and the source-time function indicates that this event comprised several distinct subevents. Each subevent is considered to have ruptured a different fault segment. This observation indicates the existence of a mechanical barrier, namely a NAF segment boundary, at the hypocenter. CMT solutions of background seismicity beneath the Aegean Sea represent strike-slip or normal faulting along the NAF or its branch faults. The tensional axes of these events are oriented northeast–southwest, indicating a transtensional tectonic regime. Beneath the Sea of Marmara, the CMT solutions represent mostly strike-slip faulting, consistent with the motion of the NAF, but we identified a normal fault event with a tensional axis parallel to the strike of the NAF. This mechanism indicates that a pull-apart basin, marking a segment boundary of the NAF, is developing there. Because ruptures of a fault system and large earthquake magnitudes are strongly controlled by the fault system geometry and fault length, mapping fault segments along NAF can help to improve the accuracy of scenarios developed for future disastrous earthquakes in the Marmara region.

In this study, we aimed to explore the S-wave velocity structure of shallow soils using microtremors in order to estimate site responses in Tekirdag and surrounding areas (NW Turkey). We collected microtremor array data at 44 sites in Tekirdag, Marmara Ereglisi, Corlu, and Muratlı. The phase velocities of Rayleigh waves were estimated from the microtremor data using a Spatial Autocorrelation method. Then, we applied a hybrid genetic simulated annealing algorithm to obtain a 1D S-wave velocity structure at each site. Comparison between the horizontal-to-vertical ratio of microtremors and computed ellipticities of the fundamental mode Rayleigh waves showed good agreement with validation models. The depth of the engineering bedrock changed from 20 to 50 m in the Tekirdag city center and along the coastline with a velocity range of 700–930 m/s, and it ranged between 10 and 65 m in Marmara Ereglisi. The average S-wave velocity of the engineering bedrock was 780 m/s in the region. We obtained average S-wave velocities in the upper 30 m to compare site amplifications. Empirical relationships between the AVs30, the site amplifications, and also average topographic slopes were established for use in future site effects microzonation studies in the region.