GNGTS 2013 - Atti del 32° Convegno Nazionale

The exploration of the Alpine chain reached the peak with the TRANSALP transect, which utilized again multidisciplinary approaches: a) seismic multichannel acquisition with vibroseis and explosives, b) a 3D control of the deep structures utilizing a supplementary spread, c) wide-angle profiles, d) gravity measurements with compilation of a new map of cross-borders Bouguer anomalies covering NE-Italy, W-Austria and Bavaria, e) recording of seismological data with a permanent stations network. Along TRANSALP profile the geophysical/geological models and the reflection seismic images with their well resolved small-scale heterogeneities (Lueschen et al. , 2006) have been extended on larger depths by teleseismic “receivers functions”, P to S converted signals, illuminating the lithosphere from below which can give information on the main converter, the M-discontinuity, or on wide velocity gradient zone. An example is given in Kummerow et al. (2004), where the base of the crust and intracrustal structures in the Eastern Alps are recognized (Fig. 3), confirming the interpretation of the Transalp seismic sections (Castellarin et al. , 2006) with a south-dipping polarity of the Europe subducted mantle. It is not so immediate with the initially presented lower resolution teleseismic tomography procedures (Lippitsch et al. , 2003), probably with a poor control of the upper crust velocities and heterogeneities and construction of tomographic sections along direction where it is difficult to resolve the laterally variable structures (old, recent). ALP 2002 experiment came again toWAR/R technique, but withmany shots, several profiles and a large number of narrow spaced recording instruments, to complete the investigation of the Eastern Alps and Central Europe (Brückl et al. , 2010). The compression between Europe and the indenting Adria microplate generated the tectonic forces for the Dinaric orogeny, active from Cretaceous to Miocene, and for the extrusion and escape of the Eastern Alps towards the unconstrained Pannonian basin. Adria is moving towards north, obliquely thrusting Fig. 2 – An example of the utilization of wide-angle fans with the crustal model and a stepwise M-discontinuity reflection images along a transect from the Po Plain to Gran Paradiso (from Thouvenot et al. , 1990, modified), intersecting Sesia-Lanzo zone and Canavese line, which marks the eastern limit of the chain (CE = seismic profile CROP-ECORS). Reflections are picked on the seismic section using a maximum amplitude criterion and traces correlation. ICMs = internal crystalline massif; ECMs= external crystalline massif. At the bottom the crustal scheme with main discontinuities across the whole Western Alpine chain: 1- European Moho, 2- Brianconnais Moho, 3 - base of the Ivrea body, 4- Adria Moho. XV GNGTS 2013 L ectio M agistralis