Seismic anisotropy along the Cyprean arc and northeast Mediterranean Sea inferred from shear wave splitting analysis

Seda Yolsal-Çevikbilen

doi:10.1016/j.pepi.2014.05.010

Seismic anisotropy along the Cyprean arc and northeast Mediterranean Sea inferred from shear wave splitting analysis

Seda Yolsal-Çevikbilen^*

^*Corresponding author for this work

Department of Geophysical Engineering

Research output: Contribution to journal › Article › peer-review

17 Citations (Scopus)

Abstract

The Cyprean arc is considered to be a convergent boundary in the Eastern Mediterranean where the African plate is being subducted beneath the Anatolian plate. Mapping the lateral variations of seismic anisotropy parameters can provide essential hints to mantle dynamics and flow patterns in relation to the geometry and style of deformation developed under different pressure, temperature conditions around the subducting African lithosphere. In this study, seismic anisotropy parameters, fast polarization directions (φ) and delay times (δt) beneath the Cyprean arc and NE Mediterranean Sea are inferred from the shear wave splitting analysis performed on core-mantle refracted teleseismic shear waves (SKS phases). Earthquake data used in the present work are extracted from the continuous recordings of 8 broad-band seismic stations located in the study region for a time period during 1999 and 2012. The overall results exhibits clear evidences of mantle anisotropy with relatively uniform NE-SW aligned fast polarization directions. No abrupt changes in fast polarization directions (φ) are observed. However, near the Dead Sea Transform Fault, φ values tend to rotate from NE-SW to N-S and NW-SE in accordance with P_n anisotropy observations. Delay times (δt) vary between 0.61s±0.10s and 1.90s±0.13s. The range of delay times are generally consistent with those observed in the mantle rather than implying a crustal anisotropy. A predominant pattern of NNE-SSW fast polarization directions that is coherent with earlier SKS splitting measurements observed beneath north, central and East Anatolia suggests a SW directed asthenospheric flow caused by slab rollback process along the Hellenic and Cyprean arcs. Furthermore, apparent splitting parameters did not exhibit any significant directional dependence which may imply possibility of the presence of anisotropic models with two-layer anisotropy or dipping axis of symmetry beneath the northeast Mediterranean Sea and Cyprean arc. Consequently, a simple, single-layered and sub-horizontal anisotropy model is tentatively suggested for the study region.

Original language	English
Pages (from-to)	112-134
Number of pages	23
Journal	Physics of the Earth and Planetary Interiors
Volume	233
DOIs	https://doi.org/10.1016/j.pepi.2014.05.010
Publication status	Published - Aug 2014

Funding

This study was supported by Istanbul Technical University Research Fund (İTÜ-BAP Project No. 36113, 2012-2013). I would like to thank Turkish National Scientific and Technological Research Foundation (TÜBİTAK), the Incorporated Research Institute of Seismology (IRIS)–Wilber II, and Boğazici University – Kandilli Observatory and Earthquake Research Institute (BU-KOERI-UDIM, İstanbul) for their support. The Generic Mapping Tools (GMT; Wessel and Smith, 1998 ), and SAC2000 ( Goldstein et al., 2003; Goldstein and Snoke, 2005 ) softwares were used to prepare the figures and to process conventional earthquake data, respectively. I am grateful to Nick Teanby for providing the SKS splitting code ( ass.f ). I would also like to express my deepest gratitude to Stephen Gao for sharing his twolayers.f code generating apparent curves of shear wave splitting parameters in case of two-layer anisotropy. I am indebted to Tuncay Taymaz, Corne Kreemer, Eric Sandvol, Erdinc Saygin, Tuna Eken, the Editor-in-Chief Vernon Cormier and an anonymous referee for their generous and valuable contributions, and judicious insightful remarks which improved the earlier version of this manuscript.

Funders	Funder number
Istanbul Technical University Research Fund	2012-2013, 36113

Keywords

Cyprean arc
Delay time
Fast polarization
Northeast Mediterranean Sea
Seismic anisotropy
Shear wave splitting

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10.1016/j.pepi.2014.05.010

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@article{13e6560145b74d44bf55bfc7de30a042,

title = "Seismic anisotropy along the Cyprean arc and northeast Mediterranean Sea inferred from shear wave splitting analysis",

abstract = "The Cyprean arc is considered to be a convergent boundary in the Eastern Mediterranean where the African plate is being subducted beneath the Anatolian plate. Mapping the lateral variations of seismic anisotropy parameters can provide essential hints to mantle dynamics and flow patterns in relation to the geometry and style of deformation developed under different pressure, temperature conditions around the subducting African lithosphere. In this study, seismic anisotropy parameters, fast polarization directions (φ) and delay times (δt) beneath the Cyprean arc and NE Mediterranean Sea are inferred from the shear wave splitting analysis performed on core-mantle refracted teleseismic shear waves (SKS phases). Earthquake data used in the present work are extracted from the continuous recordings of 8 broad-band seismic stations located in the study region for a time period during 1999 and 2012. The overall results exhibits clear evidences of mantle anisotropy with relatively uniform NE-SW aligned fast polarization directions. No abrupt changes in fast polarization directions (φ) are observed. However, near the Dead Sea Transform Fault, φ values tend to rotate from NE-SW to N-S and NW-SE in accordance with Pn anisotropy observations. Delay times (δt) vary between 0.61s±0.10s and 1.90s±0.13s. The range of delay times are generally consistent with those observed in the mantle rather than implying a crustal anisotropy. A predominant pattern of NNE-SSW fast polarization directions that is coherent with earlier SKS splitting measurements observed beneath north, central and East Anatolia suggests a SW directed asthenospheric flow caused by slab rollback process along the Hellenic and Cyprean arcs. Furthermore, apparent splitting parameters did not exhibit any significant directional dependence which may imply possibility of the presence of anisotropic models with two-layer anisotropy or dipping axis of symmetry beneath the northeast Mediterranean Sea and Cyprean arc. Consequently, a simple, single-layered and sub-horizontal anisotropy model is tentatively suggested for the study region.",

keywords = "Cyprean arc, Delay time, Fast polarization, Northeast Mediterranean Sea, Seismic anisotropy, Shear wave splitting",

author = "Seda Yolsal-{\c C}evikbilen",

year = "2014",

month = aug,

doi = "10.1016/j.pepi.2014.05.010",

language = "English",

volume = "233",

pages = "112--134",

journal = "Physics of the Earth and Planetary Interiors",

issn = "0031-9201",

publisher = "Elsevier B.V.",

}

TY - JOUR

T1 - Seismic anisotropy along the Cyprean arc and northeast Mediterranean Sea inferred from shear wave splitting analysis

AU - Yolsal-Çevikbilen, Seda

PY - 2014/8

Y1 - 2014/8

N2 - The Cyprean arc is considered to be a convergent boundary in the Eastern Mediterranean where the African plate is being subducted beneath the Anatolian plate. Mapping the lateral variations of seismic anisotropy parameters can provide essential hints to mantle dynamics and flow patterns in relation to the geometry and style of deformation developed under different pressure, temperature conditions around the subducting African lithosphere. In this study, seismic anisotropy parameters, fast polarization directions (φ) and delay times (δt) beneath the Cyprean arc and NE Mediterranean Sea are inferred from the shear wave splitting analysis performed on core-mantle refracted teleseismic shear waves (SKS phases). Earthquake data used in the present work are extracted from the continuous recordings of 8 broad-band seismic stations located in the study region for a time period during 1999 and 2012. The overall results exhibits clear evidences of mantle anisotropy with relatively uniform NE-SW aligned fast polarization directions. No abrupt changes in fast polarization directions (φ) are observed. However, near the Dead Sea Transform Fault, φ values tend to rotate from NE-SW to N-S and NW-SE in accordance with Pn anisotropy observations. Delay times (δt) vary between 0.61s±0.10s and 1.90s±0.13s. The range of delay times are generally consistent with those observed in the mantle rather than implying a crustal anisotropy. A predominant pattern of NNE-SSW fast polarization directions that is coherent with earlier SKS splitting measurements observed beneath north, central and East Anatolia suggests a SW directed asthenospheric flow caused by slab rollback process along the Hellenic and Cyprean arcs. Furthermore, apparent splitting parameters did not exhibit any significant directional dependence which may imply possibility of the presence of anisotropic models with two-layer anisotropy or dipping axis of symmetry beneath the northeast Mediterranean Sea and Cyprean arc. Consequently, a simple, single-layered and sub-horizontal anisotropy model is tentatively suggested for the study region.

AB - The Cyprean arc is considered to be a convergent boundary in the Eastern Mediterranean where the African plate is being subducted beneath the Anatolian plate. Mapping the lateral variations of seismic anisotropy parameters can provide essential hints to mantle dynamics and flow patterns in relation to the geometry and style of deformation developed under different pressure, temperature conditions around the subducting African lithosphere. In this study, seismic anisotropy parameters, fast polarization directions (φ) and delay times (δt) beneath the Cyprean arc and NE Mediterranean Sea are inferred from the shear wave splitting analysis performed on core-mantle refracted teleseismic shear waves (SKS phases). Earthquake data used in the present work are extracted from the continuous recordings of 8 broad-band seismic stations located in the study region for a time period during 1999 and 2012. The overall results exhibits clear evidences of mantle anisotropy with relatively uniform NE-SW aligned fast polarization directions. No abrupt changes in fast polarization directions (φ) are observed. However, near the Dead Sea Transform Fault, φ values tend to rotate from NE-SW to N-S and NW-SE in accordance with Pn anisotropy observations. Delay times (δt) vary between 0.61s±0.10s and 1.90s±0.13s. The range of delay times are generally consistent with those observed in the mantle rather than implying a crustal anisotropy. A predominant pattern of NNE-SSW fast polarization directions that is coherent with earlier SKS splitting measurements observed beneath north, central and East Anatolia suggests a SW directed asthenospheric flow caused by slab rollback process along the Hellenic and Cyprean arcs. Furthermore, apparent splitting parameters did not exhibit any significant directional dependence which may imply possibility of the presence of anisotropic models with two-layer anisotropy or dipping axis of symmetry beneath the northeast Mediterranean Sea and Cyprean arc. Consequently, a simple, single-layered and sub-horizontal anisotropy model is tentatively suggested for the study region.

KW - Cyprean arc

KW - Delay time

KW - Fast polarization

KW - Northeast Mediterranean Sea

KW - Seismic anisotropy

KW - Shear wave splitting

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U2 - 10.1016/j.pepi.2014.05.010

DO - 10.1016/j.pepi.2014.05.010

M3 - Article

AN - SCOPUS:84903827660

SN - 0031-9201

VL - 233

SP - 112

EP - 134

JO - Physics of the Earth and Planetary Interiors

JF - Physics of the Earth and Planetary Interiors

ER -

Seismic anisotropy along the Cyprean arc and northeast Mediterranean Sea inferred from shear wave splitting analysis

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Keywords

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