ALBERT

Beschreibung: 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 M w  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 characterized by a crossover distance at 40 km: fits our results at short distances ( r 〈40 km), whereas is better at larger distances (40〈 r 〈200 km). A frequency-dependent quality factor, Q ( f )=100( f / f ref ) 0.43 (in which f ref =1.0 Hz), is coupled to the geometrical spreading. Because of the inherent trade-off of the excitation/attenuation parameters ( and ), their specific values strongly depend on the choice made for the stress drop of the smaller earthquakes. After choosing a Brune stress drop Brune =4 MPa at M w =3.5, we were able to define (1) an effective high frequency, distance- and magnitude-independent roll-off spectral parameter, eff =0.03 s and (2) a size-dependent stress-drop parameter, which increases with moment magnitude, from Brune =4 MPa at M w  3.5 to Brune =20 MPa at M w  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.