New constraints on micro-seismicity and stress state in the western part of the North Anatolian Fault Zone

Observations from a dense seismic array

Selda Altuncu Poyraz, M. Ugur Teoman, Niyazi Turkelli, Metin Kahraman, Didem Cambaz, Ahu Mutlu, Sebastian Rost, Greg A. Houseman, David A. Thompson, David Cornwell, Murat Utkucu, Levent Gulen

Research output: Contribution to journalArticle

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Abstract

With the aim of extensively investigating the crustal structure beneath the western segment of the North Anatolian Fault Zone where it splays into northern and southern branches, a temporary seismic network (dense array for North Anatolia-DANA) consisting of 70 stations was deployed in early May 2012 and operated for 18 months in the Sakarya region during the FaultLab experiment. Out of 2437 events contaminated by explosions, we extracted 1371 well located earthquakes. The enhanced station coverage having a nominal station spacing of 7 km, lead to a minimum magnitude calculation of 0.1. Horizontal and vertical location uncertainties within the array do not exceed 0.8 km and 0.9 km, respectively. We observe considerable seismic activity along both branches of the fault where the depth of the seismogenic zone was mostly confined to 15 km. Using our current earthquake catalog we obtained a b-value of 1. We also mapped the b-value variation with depth and observed a gradual decrease. Furthermore, we determined the source parameters of 41 earthquakes with magnitudes greater than 1.8 using P-wave first motion polarity method. Regional Moment Tensor Inversion method was also applied to earthquakes with magnitudes greater than 3.0. Focal mechanism solutions confirm that Sakarya and its vicinity is stressed by a compressional regime showing a primarily oblique–slip motion character. Stress tensor analysis indicates that the maximum principal stress is aligned in WNW–ESE direction and the tensional axis is aligned in NNE–SSW direction.
Original languageEnglish
Pages (from-to)190-201
Number of pages12
JournalTectonophysics
Volume656
Early online date8 Jul 2015
DOIs
Publication statusPublished - 12 Aug 2015

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North Anatolian Fault
seismicity
fault zone
earthquakes
earthquake
stations
earthquake catalogue
moment tensor
source parameters
tensor analysis
focal mechanism
crustal structure
P-wave
explosion
stress tensors
spacing
P waves
catalogs
explosions
polarity

Keywords

  • micro-seismicity
  • North Anatolian Fault Zone (NAF)
  • stress tensor inversion
  • dense seismic array

Cite this

New constraints on micro-seismicity and stress state in the western part of the North Anatolian Fault Zone : Observations from a dense seismic array. / Altuncu Poyraz, Selda; Teoman, M. Ugur; Turkelli, Niyazi; Kahraman, Metin; Cambaz, Didem; Mutlu, Ahu; Rost, Sebastian; Houseman, Greg A.; Thompson, David A.; Cornwell, David; Utkucu, Murat; Gulen, Levent.

In: Tectonophysics, Vol. 656, 12.08.2015, p. 190-201.

Research output: Contribution to journalArticle

Altuncu Poyraz, S, Teoman, MU, Turkelli, N, Kahraman, M, Cambaz, D, Mutlu, A, Rost, S, Houseman, GA, Thompson, DA, Cornwell, D, Utkucu, M & Gulen, L 2015, 'New constraints on micro-seismicity and stress state in the western part of the North Anatolian Fault Zone: Observations from a dense seismic array', Tectonophysics, vol. 656, pp. 190-201. https://doi.org/10.1016/j.tecto.2015.06.022
Altuncu Poyraz, Selda ; Teoman, M. Ugur ; Turkelli, Niyazi ; Kahraman, Metin ; Cambaz, Didem ; Mutlu, Ahu ; Rost, Sebastian ; Houseman, Greg A. ; Thompson, David A. ; Cornwell, David ; Utkucu, Murat ; Gulen, Levent. / New constraints on micro-seismicity and stress state in the western part of the North Anatolian Fault Zone : Observations from a dense seismic array. In: Tectonophysics. 2015 ; Vol. 656. pp. 190-201.
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abstract = "With the aim of extensively investigating the crustal structure beneath the western segment of the North Anatolian Fault Zone where it splays into northern and southern branches, a temporary seismic network (dense array for North Anatolia-DANA) consisting of 70 stations was deployed in early May 2012 and operated for 18 months in the Sakarya region during the FaultLab experiment. Out of 2437 events contaminated by explosions, we extracted 1371 well located earthquakes. The enhanced station coverage having a nominal station spacing of 7 km, lead to a minimum magnitude calculation of 0.1. Horizontal and vertical location uncertainties within the array do not exceed 0.8 km and 0.9 km, respectively. We observe considerable seismic activity along both branches of the fault where the depth of the seismogenic zone was mostly confined to 15 km. Using our current earthquake catalog we obtained a b-value of 1. We also mapped the b-value variation with depth and observed a gradual decrease. Furthermore, we determined the source parameters of 41 earthquakes with magnitudes greater than 1.8 using P-wave first motion polarity method. Regional Moment Tensor Inversion method was also applied to earthquakes with magnitudes greater than 3.0. Focal mechanism solutions confirm that Sakarya and its vicinity is stressed by a compressional regime showing a primarily oblique–slip motion character. Stress tensor analysis indicates that the maximum principal stress is aligned in WNW–ESE direction and the tensional axis is aligned in NNE–SSW direction.",
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AU - Altuncu Poyraz, Selda

AU - Teoman, M. Ugur

AU - Turkelli, Niyazi

AU - Kahraman, Metin

AU - Cambaz, Didem

AU - Mutlu, Ahu

AU - Rost, Sebastian

AU - Houseman, Greg A.

AU - Thompson, David A.

AU - Cornwell, David

AU - Utkucu, Murat

AU - Gulen, Levent

N1 - Major funding was provided by the UK Natural Environment Research Council (NERC) under grant NE/I028017/1 and partially supported by Boğaziçi University Research Fund (BAP) under grant 6922. We would like to thank all the project members from the University of Leeds, Boğaziçi University, Kandilli Observatory, Aberdeen University and Sakarya University. I would also like to thank Prof. Ali Pinar and Dr. Kıvanç Kekovalı for their valuable comments. Some of the figures were generated by GMT software (Wessel and Smith, 1995).

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N2 - With the aim of extensively investigating the crustal structure beneath the western segment of the North Anatolian Fault Zone where it splays into northern and southern branches, a temporary seismic network (dense array for North Anatolia-DANA) consisting of 70 stations was deployed in early May 2012 and operated for 18 months in the Sakarya region during the FaultLab experiment. Out of 2437 events contaminated by explosions, we extracted 1371 well located earthquakes. The enhanced station coverage having a nominal station spacing of 7 km, lead to a minimum magnitude calculation of 0.1. Horizontal and vertical location uncertainties within the array do not exceed 0.8 km and 0.9 km, respectively. We observe considerable seismic activity along both branches of the fault where the depth of the seismogenic zone was mostly confined to 15 km. Using our current earthquake catalog we obtained a b-value of 1. We also mapped the b-value variation with depth and observed a gradual decrease. Furthermore, we determined the source parameters of 41 earthquakes with magnitudes greater than 1.8 using P-wave first motion polarity method. Regional Moment Tensor Inversion method was also applied to earthquakes with magnitudes greater than 3.0. Focal mechanism solutions confirm that Sakarya and its vicinity is stressed by a compressional regime showing a primarily oblique–slip motion character. Stress tensor analysis indicates that the maximum principal stress is aligned in WNW–ESE direction and the tensional axis is aligned in NNE–SSW direction.

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KW - stress tensor inversion

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JO - Tectonophysics

JF - Tectonophysics

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