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Pure and Applied Geophysics

, Volume 169, Issue 4, pp 659–675 | Cite as

An Assessment of the Seismicity of the Bursa Region from a Temporary Seismic Network

  • Elcin Gok
  • Orhan Polat
Article

Abstract

A temporary earthquake station network of 11 seismological recorders was operated in the Bursa region, south of the Marmara Sea in the northwest of Turkey, which is located at the southern strand of the North Anatolian Fault Zone (NAFZ). We located 384 earthquakes out of a total of 582 recorded events that span the study area between 28.50–30.00°E longitudes and 39.75–40.75°N latitudes. The depth of most events was found to be less than 29 km, and the magnitude interval ranges were between 0.3 ≤ ML ≤ 5.4, with RMS less than or equal to 0.2. Seismic activities were concentrated southeast of Uludag Mountain (UM), in the Kestel-Igdir area and along the Gemlik Fault (GF). In the study, we computed 10 focal mechanisms from temporary and permanents networks. The predominant feature of the computed focal mechanisms is the relatively widespread near horizontal northwest-southeast (NW–SE) T-axis orientation. These fault planes have been used to obtain the orientation and shape factor (R, magnitude stress ratio) of the principal stress tensors (σ1, σ2, σ3). The resulting stress tensors reveal σ1 closer to the vertical (oriented NE–SW) and σ2, σ3 horizontal with R = 0.5. These results confirm that Bursa and its vicinity could be defined by an extensional regime showing a primarily normal to oblique-slip motion character. It differs from what might be expected from the stress tensor inversion for the NAFZ. Different fault patterns related to structural heterogeneity from the north to the south in the study area caused a change in the stress regime from strike-slip to normal faulting.

Keywords

Bursa region seismicity focal mechanism stress tensor 

Notes

Acknowledgments

This paper is a part of the PhD thesis of Elcin Gok. Electronic files of this study can be downloaded at http://people.deu.edu.tr/elcin.gok/bursa.html. We are grateful to the staff of the GeoForschungZentrum (GFZ) of Potsdam, Germany for the installation of the temporary seismic network. We wish to thank Mahmut Parlaktuna from the Middle East Technical University (METU) in Ankara, Claus Milkereit from the GFZ (Potsdam) and Asaf Pekdeger from Frei University of Berlin, who cooperated with us during the project duration. We also acknowledge Rahmi Pinar, Zafer Akcig and Zulfikar Erhan from Dokuz Eylul University (DEU) in Izmir for facilitating our works during and after the project. We are grateful to Dogan Kalafat, Mehmet Yilmazer and Selda Altuncu from the Kandilli Observatory and Earthquake Research Institute (KOERI) for providing digital broad-band data and the zSacWin program code. Most of the figures were generated by using the GMT software package (Wessel and Smith, 1995). This manuscript greatly benefited from helpful reviews by the editor, Prof. Eugenio Carminati. We would like to also express our special thanks to two anonymous reviewers for their comments and constructive criticisms which have greatly improved the earlier version of the paper. This work was supported by the TUBITAK (Turkey) and JULICH (Germany) bilateral scientific agreement (Project 102Y156). This study was also granted by the Scientific Research Project of the Dokuz Eylul University (DEU-BAP 2006.KB.FEN.007). The English language was edited by Barbara Jean Isenberg (http://www.barbarajisenberg.com).

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© Springer Basel AG 2011

Authors and Affiliations

  1. 1.Earthquake Research and Implementation CenterDokuz Eylul UniversityIzmirTurkey
  2. 2.Department of Geophysics, Engineering FacultyDokuz Eylul UniversityIzmirTurkey

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