A study of microearthquake seismicity and focal mechanisms within the Sea of Marmara (NW Turkey) using ocean bottom seismometers (OBSs)

Toshinori Sato, Junzo Kasahara, Tuncay Taymaz*, Masakazu Ito, Aya Kamimura, Tadaaki Hayakawa, Onur Tan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

64 Citations (Scopus)

Abstract

We have carried out seismological observations within the Sea of Marmara (NW Turkey) in order to investigate the seismicity induced after Gölcükü-İzmit (Kocaeli) earthquake (Mw 7.4) of August 17, 1999, using ocean bottom seismometers (OBSs). High-resolution hypocenters and focal mechanisms of microearthquakes have been investigated during this Marmara Sea OBS project involving deployment of 10 OBSs within the Çinarcik (eastern Marmara Sea) and Central-Tekirdaǧ (western Marmara Sea) basins during April-July 2000. Little was known about microearthquake activity and their source mechanisms in the Marmara Sea. We have detected numerous microearthquakes within the main basins of the Sea of Marmara along the imaged strands of the North Anatolian Fault (NAF). We obtained more than 350 well-constrained hypocenters and nine composite focal mechanisms during 70 days of observation. Microseismicity mainly occurred along the Main Marmara Fault (MMF) in the Marmara Sea. There are a few events along the Southern Shelf. Seismic activity along the Main Marmara Fault is quite high, and focal depth distribution was shallower than 20 km along the western part of this fault, and shallower than 15 km along its eastern part. From high-resolution relative relocation studies of some of the microearthquake clusters, we suggest that the western Main Marmara Fault is subvertical and the eastern Main Marmara Fault dips to south at ∼45°. Composite focal mechanisms show a strike-slip regime on the western Main Marmara Fault and complex faulting (strike-slip and normal faulting) on the eastern Main Marmara Fault.

Original languageEnglish
Pages (from-to)303-314
Number of pages12
JournalTectonophysics
Volume391
Issue number1-4 SPEC.ISS.
DOIs
Publication statusPublished - 29 Oct 2004

Funding

We are grateful to NATO (grant no: 976744), the Institut de Physique du Globe de Paris, TÜBİTAK, TÜBA and Istanbul Technical University for supporting this Marmara Sea OBS and Land Seismograph Project and for helping us to conduct this experiment following the destructive earthquake of August 17, 1999. We would like to acknowledge the support given by A.M. Celâl Şengör, Xavier Le Pichon, Naci Görür, and Gülsün Sağlamer, and also thank the Hydrographic Department of the Turkish Navy, the captains and crews of Turkish Navy Research Vessel Çubuklu and other boats of the Turkish Navy, the Coastguard, and the mayor of Marmara Island for their professional and effective assistance, which ensured the completion of the cruises under some difficult circumstances and conditions. We also thank Tuğrul Genç, Emin Demirbağ and Argun Kocaoğlu for helping us during deployment and recovery of OBSs. Rob Westaway and anonymous reviewers provided helpful comments on this manuscript. The figures were generated using the GMT software (University of Hawaii; Wessel and Smith, 1998 ). This work has also been supported by TÜBİTAK–YDABAG projects 100Y082 and 101Y069, and by the Turkish Academy of Sciences (TÜBA), in the framework of their Young Scientist Award Programme (Tuncay Taymaz /TÜBA-GEBİP/2001-2-17).

FundersFunder number
Tuncay Taymaz/TÜBA-GEBİP/2001-2-17
TÜBİTAK100Y082, 101Y069
North Atlantic Treaty Organization976744
Türkiye Bilimler Akademisi
Istanbul Teknik Üniversitesi
Institut de Physique du Globe de Paris

    Keywords

    • Earthquakes
    • Fault mechanisms
    • Marmara sea
    • Ocean bottom seismology
    • Seismotectonics
    • Turkey

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