High-resolution 3-D P-wave model of the Alpine crust

The 3-D P-wave velocity structure of the Alpine crust has been determined from local earthquake tomography using a set of high-quality travel-time data. The application of an algorithm combining accurate phase picking with an automated quality assessment allowed the re-picking of first arriving P-phases from the original seismograms. The quality and quantity of the re-picked phase data used in this study allows the 3-D imaging of large parts of the Alpine lithosphere between 0 and 60 km depth. Our model represents a major improvement in terms of reliability and resolution compared to any previous regional tomographic studies of the Alpine crust. First order anomalies like crust-mantle boundary (Moho) and the Ivrea body in the Western Alps are well resolved and in good agreement with previous studies. In addition, several (consistent) small-scale anomalies are visible in the tomographic image. A clear continuation of the lower European crust beneath the Adriatic Moho in the Central Alps is not observed in our results. The absence of such a signature may indicate the eclogitization of the subducted European lower crust in the Central Alps. In agreement with previous results, the additional analysis of focal depths in our new 3-D P-wave model shows that all studied earthquakes in the northern foreland have occurred within the European crust. Waveforms and focal depths suggest that at least one of the analyzed events south of the Alps is located in the Adriatic mantle.