Investigation on regional attenuation of Vrancea (Romania) intermediate-depth earthquakes

This paper aims at investigating possible regional attenuation patterns in the case of Vrancea (Romania) intermediate-depth earthquakes. Almost 500 pairs of horizontal components recorded during 13 intermediate-depth Vrancea earthquakes are employed in order to evaluate the regional attenuation patterns. The recordings are grouped according to the azimuth with regard to the Vrancea seismic source and subsequently, Q models are computed for each azimuthal zone assuming similar geometrical spreading. Moreover, the local soil amplification which was disregarded in a previous analysis performed for Vrancea intermediate-depth earthquakes is now clearly evaluated. The results show minor differences between the four regions situated in front of the Carpathian Mountains and considerable differences in attenuation of seismic waves between the forearc and backarc regions (with regard to the Carpathian Mountains). Consequently, an average Q model of the type Q(f) = 115×f 1.25 is obtained for the four forearc regions, while a separate Q model of the type Q(f) = 70×f0.90 is computed for the backarc region. These results highlight the need to evaluate the seismic hazard of Romania by using ground motion models which take into account the different attenuation between the forearc/backarc regions.