AN INTERPRETATION OF THE DEEP SEISMIC LINES FROM THE PENNINIC ALPS OFVALAIS (SWITZERLAND)

The upper part of three deep seismic lines running across the Penninic Swiss Alps of Valais have been studied. Numerous reflectors illustrat e the nappe structure of this internal part of the orogen. These refle ctors, even at great depths (20-25 km), can be correlated with outcrop ping geological features and are most likely produced by lithological boundaries rather than by mylonites zones, which are hardly reflective in such an environment. Our interpretations, largely constrained by p rojections of the outcropping geology, have improved our knowledge of the deep structure of this segment of the Alpine belt, enhancing the i mportance of the backfolding and the crustal scale deformation phase w hich produced the Rawil-Valpelline depression and the Aar-Toce culmina tion. Furthermore we have here the possibility of correlating seismic patterns produced by ductile folds with the outcropping structures.