ALPASS - Passive seismic monitoring in the Eastern Alps

Seismic exploration of the Eastern Alpine lithosphere by WARR-experiments (Wide-Angle Refraction and Reflection) started about 40 years ago. The most recent and most ambitious WARR-experiments were CELEBRATION 2000 and ALP 2002 and they covered the Eastern Alps area with a net of profiles, thus approaching a 3D geometry. The TRANSALP profile (1998 - 2001) produced a representative lithospheric section across the Eastern Alps between Munich and Verona by the integration of Vibroseis, wide angle and teleseismic data. A tomographic inversion of regional teleseismic data resolved the P-wave velocities of the mantle down to a depth of 400 km. These results as well as the reinterpretation of older data provide a relatively detailed conception of crustal structure, the shape of the Moho, and low temperature zones in the mantle indicating down going slabs. However, the direction of subduction of the colliding European and the Adriatic plates is a matter of controversial interpretations. Other key questions about the Eastern Alpine region include for example the existence of a triple junction at the transition to the Dinarides and the nature of the deep structures associated with extrusion towards the Pannonian basin. In order to elucidate these questions ALPASS has been started as an international (Austria, Croatia, Finland, Hungary, Poland and USA) passive seismic monitoring program covering the Eastern Alps and neighbouring tectonic provinces between 45° - 50° N and 13° - 18° E. Up to 80 temporary seismic recording stations have been deployed for the period of May 2005 and May 2006, and teleseismic data from about 160 permanent stations in a larger area are collected regularly. ALPASS has been designed to mutually support other contemporary seismic monitoring programs (BOHEMA, Pannonian Basin Project). Data will be evaluated by receiver function analysis and teleseismic P-wave and surface wave tomography. The determination of hypocenters for local earthquakes and calculation of crustal traveltime corrections for teleseismic phases take advantage of the accurate P-wave velocity model of the crust derived from the recent WARR experiments. The instrumentation is working well and examples of data and preliminary processing results will be presented.