Crustal-scale shear zones and heterogeneous structure beneath the North Anatolian Fault Zone, Turkey, revealed by a high-density seismometer array

Metin Kahraman, David G Cornwell, David A Thompson, Sebastian Rost, Gregory A Houseman, Niyazi Turkelli, Ugur Teoman, Selda Altuncu Poyraz, Murat Utkucu, Levent Gulen

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Abstract

Continental scale deformation is often localised along strike-slip faults constituting considerable seismic hazard in many locations. Nonetheless, the depth extent and precise geometry of such faults, key factors in how strain is accumulated in the earthquake cycle and the assessment of seismic hazard, are poorly constrained in the mid to lower crust. Using a dense broadband network of 71 seismic stations with a nominal station spacing of 7 km in the vicinity of the 1999 Izmit earthquake we map previously unknown small-scale structure in the crust and upper mantle along this part of the North Anatolian Fault Zone (NAFZ). We show that lithological and structural variations exist in the upper, mid and lower crust on length scales of less than 10 km and less than 20 km in the upper mantle. The surface expression of the NAFZ in this region comprises two major branches; both are shown to continue at depth with differences in dip, depth extent and (possibly) width. We interpret a <10 km wide northern branch that passes downward into a shear zone that traverses the entire crust and penetrates the upper mantle to a depth of at least 50 km. The dip of this structure appears to decrease west–east from ∼90° to ∼65° to the north over a distance of 30 to 40 km. Deformation along the southern branch may be accommodated over a wider (>10 km) zone in the crust with a similar variation of dip but there is no clear evidence that this shear zone penetrates the Moho. Layers of anomalously low velocity in the mid crust (20–25 km depth) and high velocity in the lower crust (extending from depths of 28–30 km to the Moho) are best developed in the Armutlu–Almacik block between the two shear zones. A mafic lower crust, possibly resulting from ophiolitic obduction or magmatic intrusion, can best explain the coherent lower crustal structure of this block. Our images show that strain has developed in the lower crust beneath both northern and southern strands of the North Anatolian Fault. Our new high resolution images provide new insights into the structure and evolution of the NAFZ and show that a small and dense passive seismic network is able to image previously undetectable crust and upper mantle heterogeneity on lateral length scales of less than 10 km.
Original languageEnglish
Pages (from-to)129-139
Number of pages11
JournalEarth and Planetary Science Letters
Volume430
Early online date28 Aug 2015
DOIs
Publication statusPublished - 15 Nov 2015

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Seismographs
North Anatolian Fault
seismographs
Turkey
seismograph
lower crust
shear zone
fault zone
crusts
Earthquakes
Hazards
Strike-slip faults
shear
Broadband networks
crust
upper mantle
Image resolution
Moho
seismic hazard
dip

Keywords

  • Anatolia
  • strike-slip fault
  • receiver function
  • seismology
  • shear zone
  • tectonics

Cite this

Crustal-scale shear zones and heterogeneous structure beneath the North Anatolian Fault Zone, Turkey, revealed by a high-density seismometer array. / Kahraman, Metin; Cornwell, David G; Thompson, David A; Rost, Sebastian; Houseman, Gregory A; Turkelli, Niyazi; Teoman, Ugur; Altuncu Poyraz, Selda; Utkucu, Murat; Gulen, Levent.

In: Earth and Planetary Science Letters, Vol. 430, 15.11.2015, p. 129-139.

Research output: Contribution to journalArticle

Kahraman, Metin ; Cornwell, David G ; Thompson, David A ; Rost, Sebastian ; Houseman, Gregory A ; Turkelli, Niyazi ; Teoman, Ugur ; Altuncu Poyraz, Selda ; Utkucu, Murat ; Gulen, Levent. / Crustal-scale shear zones and heterogeneous structure beneath the North Anatolian Fault Zone, Turkey, revealed by a high-density seismometer array. In: Earth and Planetary Science Letters. 2015 ; Vol. 430. pp. 129-139.
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abstract = "Continental scale deformation is often localised along strike-slip faults constituting considerable seismic hazard in many locations. Nonetheless, the depth extent and precise geometry of such faults, key factors in how strain is accumulated in the earthquake cycle and the assessment of seismic hazard, are poorly constrained in the mid to lower crust. Using a dense broadband network of 71 seismic stations with a nominal station spacing of 7 km in the vicinity of the 1999 Izmit earthquake we map previously unknown small-scale structure in the crust and upper mantle along this part of the North Anatolian Fault Zone (NAFZ). We show that lithological and structural variations exist in the upper, mid and lower crust on length scales of less than 10 km and less than 20 km in the upper mantle. The surface expression of the NAFZ in this region comprises two major branches; both are shown to continue at depth with differences in dip, depth extent and (possibly) width. We interpret a <10 km wide northern branch that passes downward into a shear zone that traverses the entire crust and penetrates the upper mantle to a depth of at least 50 km. The dip of this structure appears to decrease west–east from ∼90° to ∼65° to the north over a distance of 30 to 40 km. Deformation along the southern branch may be accommodated over a wider (>10 km) zone in the crust with a similar variation of dip but there is no clear evidence that this shear zone penetrates the Moho. Layers of anomalously low velocity in the mid crust (20–25 km depth) and high velocity in the lower crust (extending from depths of 28–30 km to the Moho) are best developed in the Armutlu–Almacik block between the two shear zones. A mafic lower crust, possibly resulting from ophiolitic obduction or magmatic intrusion, can best explain the coherent lower crustal structure of this block. Our images show that strain has developed in the lower crust beneath both northern and southern strands of the North Anatolian Fault. Our new high resolution images provide new insights into the structure and evolution of the NAFZ and show that a small and dense passive seismic network is able to image previously undetectable crust and upper mantle heterogeneity on lateral length scales of less than 10 km.",
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author = "Metin Kahraman and Cornwell, {David G} and Thompson, {David A} and Sebastian Rost and Houseman, {Gregory A} and Niyazi Turkelli and Ugur Teoman and {Altuncu Poyraz}, Selda and Murat Utkucu and Levent Gulen",
note = "Acknowledgements DANA (Dense Array for Northern Anatolia) is part of the Faultlab project, a collaborative effort by the University of Leeds, Bogazi{\cc}i University Kandilli Observatory and Earthquake Research Institute (BU-KOERI) and Sakarya University. Major funding was provided by the UK Natural Environment Research Council (NERC) under grant NE/I028017/1. Equipment was provided and supported by the NERC Geophysical Equipment Facility (SEIS-UK) Loan 947. This project is also supported by Bogazi{\cc}i ˘ University Scientific Research Projects (BAP) under grant 6922 and Turkish State Planning Organization (DPT) under the TAM project, number 2007K120610. The authors thank the Editor, two anonymous reviewers and A. Arda {\"O}zacar for their comments which improved the manuscript.",
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T1 - Crustal-scale shear zones and heterogeneous structure beneath the North Anatolian Fault Zone, Turkey, revealed by a high-density seismometer array

AU - Kahraman, Metin

AU - Cornwell, David G

AU - Thompson, David A

AU - Rost, Sebastian

AU - Houseman, Gregory A

AU - Turkelli, Niyazi

AU - Teoman, Ugur

AU - Altuncu Poyraz, Selda

AU - Utkucu, Murat

AU - Gulen, Levent

N1 - Acknowledgements DANA (Dense Array for Northern Anatolia) is part of the Faultlab project, a collaborative effort by the University of Leeds, Bogaziçi University Kandilli Observatory and Earthquake Research Institute (BU-KOERI) and Sakarya University. Major funding was provided by the UK Natural Environment Research Council (NERC) under grant NE/I028017/1. Equipment was provided and supported by the NERC Geophysical Equipment Facility (SEIS-UK) Loan 947. This project is also supported by Bogaziçi ˘ University Scientific Research Projects (BAP) under grant 6922 and Turkish State Planning Organization (DPT) under the TAM project, number 2007K120610. The authors thank the Editor, two anonymous reviewers and A. Arda Özacar for their comments which improved the manuscript.

PY - 2015/11/15

Y1 - 2015/11/15

N2 - Continental scale deformation is often localised along strike-slip faults constituting considerable seismic hazard in many locations. Nonetheless, the depth extent and precise geometry of such faults, key factors in how strain is accumulated in the earthquake cycle and the assessment of seismic hazard, are poorly constrained in the mid to lower crust. Using a dense broadband network of 71 seismic stations with a nominal station spacing of 7 km in the vicinity of the 1999 Izmit earthquake we map previously unknown small-scale structure in the crust and upper mantle along this part of the North Anatolian Fault Zone (NAFZ). We show that lithological and structural variations exist in the upper, mid and lower crust on length scales of less than 10 km and less than 20 km in the upper mantle. The surface expression of the NAFZ in this region comprises two major branches; both are shown to continue at depth with differences in dip, depth extent and (possibly) width. We interpret a <10 km wide northern branch that passes downward into a shear zone that traverses the entire crust and penetrates the upper mantle to a depth of at least 50 km. The dip of this structure appears to decrease west–east from ∼90° to ∼65° to the north over a distance of 30 to 40 km. Deformation along the southern branch may be accommodated over a wider (>10 km) zone in the crust with a similar variation of dip but there is no clear evidence that this shear zone penetrates the Moho. Layers of anomalously low velocity in the mid crust (20–25 km depth) and high velocity in the lower crust (extending from depths of 28–30 km to the Moho) are best developed in the Armutlu–Almacik block between the two shear zones. A mafic lower crust, possibly resulting from ophiolitic obduction or magmatic intrusion, can best explain the coherent lower crustal structure of this block. Our images show that strain has developed in the lower crust beneath both northern and southern strands of the North Anatolian Fault. Our new high resolution images provide new insights into the structure and evolution of the NAFZ and show that a small and dense passive seismic network is able to image previously undetectable crust and upper mantle heterogeneity on lateral length scales of less than 10 km.

AB - Continental scale deformation is often localised along strike-slip faults constituting considerable seismic hazard in many locations. Nonetheless, the depth extent and precise geometry of such faults, key factors in how strain is accumulated in the earthquake cycle and the assessment of seismic hazard, are poorly constrained in the mid to lower crust. Using a dense broadband network of 71 seismic stations with a nominal station spacing of 7 km in the vicinity of the 1999 Izmit earthquake we map previously unknown small-scale structure in the crust and upper mantle along this part of the North Anatolian Fault Zone (NAFZ). We show that lithological and structural variations exist in the upper, mid and lower crust on length scales of less than 10 km and less than 20 km in the upper mantle. The surface expression of the NAFZ in this region comprises two major branches; both are shown to continue at depth with differences in dip, depth extent and (possibly) width. We interpret a <10 km wide northern branch that passes downward into a shear zone that traverses the entire crust and penetrates the upper mantle to a depth of at least 50 km. The dip of this structure appears to decrease west–east from ∼90° to ∼65° to the north over a distance of 30 to 40 km. Deformation along the southern branch may be accommodated over a wider (>10 km) zone in the crust with a similar variation of dip but there is no clear evidence that this shear zone penetrates the Moho. Layers of anomalously low velocity in the mid crust (20–25 km depth) and high velocity in the lower crust (extending from depths of 28–30 km to the Moho) are best developed in the Armutlu–Almacik block between the two shear zones. A mafic lower crust, possibly resulting from ophiolitic obduction or magmatic intrusion, can best explain the coherent lower crustal structure of this block. Our images show that strain has developed in the lower crust beneath both northern and southern strands of the North Anatolian Fault. Our new high resolution images provide new insights into the structure and evolution of the NAFZ and show that a small and dense passive seismic network is able to image previously undetectable crust and upper mantle heterogeneity on lateral length scales of less than 10 km.

KW - Anatolia

KW - strike-slip fault

KW - receiver function

KW - seismology

KW - shear zone

KW - tectonics

U2 - 10.1016/j.epsl.2015.08.014

DO - 10.1016/j.epsl.2015.08.014

M3 - Article

VL - 430

SP - 129

EP - 139

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

SN - 0012-821X

ER -