Three-dimensional VP and VP /VS models of the upper crust in the Friuli area (northeastern Italy) |
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| Authors: | G F Gentile G Bressan L Burlini & R De Franco |
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| Institution: | Osservatorio Geofisico Sperimentale, Dip. OGA, Borgo Grotta Gigante 42/c, 34100 Sgonico, Trieste, Italy. E-mail:;, Osservatorio Geofisico Sperimentale, Dip. CRS, CPI Cussignacco, 3100 Udine, Italy. E-mail:;, ETH Zentrum, Rock Deformation Lab, Sonneggstrasse 5, 8092 Zürich, Switzerland. E-mail:;, Consiglio Nazionale delle Ricerche, IRRS, Via Bassini 15, 20133 Milano. Italy. E-mail: |
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| Abstract: | 3-D images of P velocity and P - to S -velocity ratio have been produced for the upper crust of the Friuli area (northeastern Italy) using local earthquake tomography. The data consist of 2565 P and 930 S arrival times of high quality. The best-fitting V P and V P / V S 1-D models were computed before the 3-D inversion. V P was measured on two rock samples representative of the investigated upper layers of the Friuli crust. The tomographic V P model was used for modelling the gravity anomalies, by converting the velocity values into densities along three vertical cross-sections. The computed gravity anomalies were optimized with respect to the observed gravity anomalies. The crust investigated is characterized by sharp lateral and deep V P and V P / V S anomalies that are associated with the complex geological structure. High V P / V S values are associated with highly fractured zones related to the main faulting pattern. The relocated seismicity is generally associated with sharp variations in the V P / V S anomalies. The V P images show a high-velocity body below 6 km depth in the central part of the Friuli area, marked also by strong V P / V S heterogeneities, and this is interpreted as a tectonic wedge. Comparison with the distribution of earthquakes supports the hypothesis that the tectonic wedge controls most of the seismicity and can be considered to be the main seismogenic zone in the Friuli area. |
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| Keywords: | earthquakes gravity anomalies seismotectonics tomography |
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