Abstract

We provide a complete description of the characteristics of excitation and attenuation of the ground motion in the Lake Van region (eastern Turkey) using a data set that includes three‐component seismograms from the 23 October 2011 Mw 7.1 Van earthquake, as well as its aftershocks. Regional attenuation and source scaling are parameterized to describe the observed ground motions as a function of distance, frequency, and magnitude.

Peak ground velocities are measured in selected narrow frequency bands from 0.25 to 12.5 Hz; observed peaks are regressed to define a piecewise linear regional attenuation function, a set of excitation terms, and a set of site response terms. Results are modeled through random vibration theory (see Cartwright and Longuet‐Higgins, 1956).

In the log–log space, the regional crustal attenuation is modeled with a bilinear geometrical spreading forumla characterized by a crossover distance at 40 km: forumla fits our results at short distances (r<40  km), whereas forumla is better at larger distances (40<r<200  km). A frequency‐dependent quality factor, Q(f)=100(f/fref)0.43 (in which fref=1.0  Hz), is coupled to the geometrical spreading.

Because of the inherent trade‐off of the excitation/attenuation parameters (Δσ and κ), their specific values strongly depend on the choice made for the stress drop of the smaller earthquakes. After choosing a Brune stress drop ΔσBrune=4  MPa at Mw=3.5, we were able to define (1) an effective high frequency, distance‐ and magnitude‐independent roll‐off spectral parameter, κeff=0.03  s and (2) a size‐dependent stress‐drop parameter, which increases with moment magnitude, from ΔσBrune=4  MPa at Mw 3.5 to ΔσBrune=20  MPa at Mw 7.1.

The set of parameters mentioned here may be used in order to predict the earthquake‐induced ground motions expected from future earthquakes in the region surrounding Lake Van.

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