NAF Experiment Seismic Anisotropy Beneath Northern Anatolia From Shear Wave Splitting

Date

2008-12-15

Author

Biryol, C. Berk
Zandt, George
Beck, Susan L.
Gans, Christine R.
Özacar, Atilla Arda
Tok, Hande
KOÇYİĞİT, ALİ
Bozkurt, Erdin
TAYMAZ, TUNCAY

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The North Anatolian Fault (NAF) is a 1400 km long transcurrent structure located at the northern margin of the westward-extruding Anatolian plate. Despite numerous geological studies along the fault, the deeper structure of this plate margin remains relatively unknown. One important question that can be addressed is the degree of coherency between the strain field in the upper crust and the upper mantle. Another unaddressed question concerns the lateral extent of the shear zone at depth associated with the North Anatolian Fault. In order to compare the deep structure of the fault with major transcurrent or transpressive structures such as the Alpine Fault (New Zealand) and the San Andreas Fault (Western North America), we analyzed mantle anisotropy beneath NAF array, a 39 station broadband passive seismic array, using shear- wave splitting observed by SKS and SKKS phases. Our results indicated that the observed mantle strain field is uniform underneath the array with consistently NE-SW trending fast directions. This trend remains parallel or sub-parallel to the absolute plate motion vectors with a no net rotation reference frame calculated using Global Strain Rate Model (GSRM). The observations of fast polarization directions agree well with the orientations of the modeled smallest principle strain rate axis (GSRM). This indicates that the upper-mantle and upper-crust are deforming coherently, suggesting the existence of either strong coupling or similar boundary conditions. We observed that the anisotropy directions do not vary across the NAF. This might suggest that the NAF and the associated plate boundary is limited to the crust and does not extend into the upper mantle. This is in contrast to observations from the southern San Andreas Fault and Alpine Fault. The uniformity of the fast polarization directions throughout the study area also favors an asthenospheric source for anisotropy rather than a lithospheric source. Lag times between the fast and slow polarizations measured for the study area varies within the range of 0.5 seconds to 1.6 seconds. Lower lag times are obtained consistently at the eastern part of the array. The lower values of delay times might suggest either a locally thinner anisotropic source or weaker anisotropy in the upper mantle.

URI

http://abstractsearch.agu.org/meetings/2008/FM/sections/T/sessions/T21A/abstracts/T21A-1916.html
https://hdl.handle.net/11511/94771

Conference Name

American Geophysical Union (AGU) 2008 Fall Meeting

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Department of Geological Engineering, Conference / Seminar

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Citation Formats

C. B. Biryol et al., “NAF Experiment Seismic Anisotropy Beneath Northern Anatolia From Shear Wave Splitting,” San-Francisco, Kostarika, 2008, vol. 89, Accessed: 00, 2021. [Online]. Available: http://abstractsearch.agu.org/meetings/2008/FM/sections/T/sessions/T21A/abstracts/T21A-1916.html.