University of Cambridge > Talks.cam > Bullard Laboratories Wednesday Seminars > Lithospheric structure, anisotropy and seismicity of the active North Anatolian Fault, Turkey

Lithospheric structure, anisotropy and seismicity of the active North Anatolian Fault, Turkey

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The collective seismological results from the Dense Array for Northern Anatolia (DANA) will be presented in this talk. DANA was part of the multi-disciplinary Faultlab project, designed to collect passive seismological data across the seismically-active North Anatolian Fault in northern Turkey to image the fault structure in the lower crust and upper mantle. The North Anatolian Fault Zone (NAFZ) is a major continental strike-slip fault system that extends ~1200 km across Turkey. Our study region samples the NAFZ near the epicentres of two large earthquakes that occurred in 1999 at Izmit (M7.5) and Düzce (M7.2) and where estimates of present-day slip rate are 20-25 mm/yr. Using recordings of teleseismic earthquakes from a rectangular seismometer array spanning the NAFZ with 66 stations at a nominal inter-station spacing of 7 km and 7 additional stations further afield, we build a detailed 3-D image of structure and anisotropy using receiver functions, tomography and shear wave splitting and illuminate major changes in the architecture and properties of the upper crust, lower crust and upper mantle, both across and along the two branches of the NAFZ , at length scales of less than 20 km. Recent work with the DANA dataset has improved the earthquake catalogue and applied harmonic analysis of receiver functions with local and teleseismic shear wave splitting constrain zones of anisotropy in the crust and mantle. We show that the northern NAFZ branch depth extent varies from the mid-crust to the upper mantle and it is likely to be less than 10 km wide. A high velocity lower crust and a region of crustal underthrusting appear to add strength to a heterogeneous crust and play a role in dictating the variation in faulting style and post-seismic deformation. Sharp changes in lithospheric mantle velocity and anisotropy are constrained as the NAFZ is crossed, whereas crustal structure and anisotropy vary considerably both parallel and perpendicular to the faulting. We use our observations to test current models of the localisation of strike-slip deformation and develop new ideas to explain how narrow fault zones develop in heterogeneous lithosphere.

References: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017JB015386 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL072726 https://www.sciencedirect.com/science/article/pii/S0012821X15005348 https://www.sciencedirect.com/science/article/pii/S0040195115003522

This talk is part of the Bullard Laboratories Wednesday Seminars series.

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