Velocity contrast across the 1944 rupture zone of the North Anatolian fault east of Ismetpasa from analysis of teleseismic arrivals

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Abstract

[1] We use differences between arrival times of teleseismic events at sets of stations crossing the North Anatolian fault east of Ismetpasa, where shallow creep has been observed, to detect and quantify a contrast of seismic velocities across the fault. Waveform cross correlations are utilized to calculate phase delays of P waves with respect to expected teleseismic arrivals with incident angles corresponding to the generating events. Compiled delay times associated with 121 teleseismic events indicate about 4.3% average P wave velocity contrast across the fault over the top 36 km, with faster velocity on the north side. The estimated contrast is about 8.3% if the velocity contrast is limited to the top 18 km. The sense of velocity contrast is consistent with the overall tectonic setting and inference made for the examined fault section based on theoretical expectations for bimaterial ruptures and observed asymmetry of rock damage across the fault. Our data indicate lack of significant microseismicity near the fault, suggesting that creep in the area is limited to the depth section above the seismogenic zone.

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