engleski

Azimuthal anisotropy of Pg-wave velocity in hypocentral volumes of NW Croatia

Based on a large set of arrival times of the Pg-phase reported by local and regional stations, we estimate azimuthal anisotropy of the Pg-wave velocity in focal volumes of the upper crust in NW Croatia. The method is based on analyses of the azimuthal dependence of ratios of cumulative differences of arrival times and travel paths between foci of earthquake pairs, computed for rays propagating within narrow azimuthal windows. The results clearly indicate presence of anisotropy with the direction of fast waves (approximately NNE– SSW) coinciding with the direction of the maximum tectonic pressure as revealed by 23 available focal mechanisms and previous geological investigations. A large part of observed anisotropy may be explained if hypocentral volume is assumed to be pervaded by a system of vertical extensive-dilatancy anisotropy (EDA) cracks aligned under the influence of local tectonic stress field.

Azimuthal velocity anisotropy ; tectonic stress field ; EDA ; Croatia

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