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

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• 作者：Marijan Herak (1)
  Davorka Herak (1)
  Josip Stip?evi? (1)
  
• 关键词：azimuthal velocity anisotropy ; tectonic stress field ; extensive ; dilatancy anisotropy ; Croatia
• 刊名：Acta Geophysica
• 出版年：2009
• 出版时间：September 2009
• 年：2009
• 卷：57
• 期：3
• 页码：600-615
• 全文大小：888KB
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• 作者单位：Marijan Herak (1)
  Davorka Herak (1)
  Josip Stip?evi? (1)
  
  1. Faculty of Science and Mathematics, Department of Geophysics, University of Zagreb, Zagreb, Croatia
  
• ISSN：1895-7455

文摘

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 the presence of anisotropy of 3.3% with the direction of fast velocity (approximately NNE-SSW) coinciding with the direction of the maximum tectonic pressure as revealed by 23 available focal mechanisms and previous geological investigations. Although a large part of observed anisotropy can be explained assuming that focal volumes are pervaded by a system of vertical extensive-dilatancy anisotropy (EDA) cracks aligned under the influence of local tectonic stress field, there is indication that -to a smaller extent -some role was also played by alignment of structural features in the region.