The Simplon Normal Fault Zone is one of the largest Late Tertiary structures in the Alps which indicate extension. The structure extends from the Simplon Pass (Wallis/Switzerland) towards the Isorno Valley, northeast of Domodossola (Italy). It consists of a km-wide mylonitezone in the footwall which merges into a cataclasite belt in the hangingwall. For the kinematic analysis of the mostly brittle-deformed hanging wall, associated with the Gd. St. Bernhard Nappe, data of slickensides and extension joints were taken. Additionally selected fault striae populations with definite shear sense were investigated.

With respect to the orientation, kinematics and overprinting relationship it was possible to identify two phases of deformation: an older one, indicated by normal faults directed southwest, and a younger one consisting of thrusts and reverse faults. All together 266 normal faults, and 25 thrusts and reverse faults were measured.

With this kinematic data a paleostress analysis was carried out. We have used the P/T-method and the P- and T-dihedra method as graphical methods, as well the direct inversion method for a mathematical determination of principal stess direction. The early deformation phase shows gently SW - NE diping s3-axis and steep diping s1-axis. The direction of ductile extension axis on the Simplon Fault Zone has been determined by mineral streching lineations and shear bands indicating top to SW. Therefore it is proposed that mylonites and brittle deformation formed in the same stress regime. The evaluated direction is in good agreement with the ductile extension axis of the mylonite at the Simplon Fault Zone described in literature.

The younger reverse faults indicate steep s3-axis and gently NW-SE directed s1-axis. The orientation of the s1-axis is corresponding to the results of earthquake data and perpendicular to the foldaxial plane of the youngest generation of folds. Based on this new data we propose a young, possibly still-persisting NW-SE compression overprinting the crustal extension indicated by the Simplon Fault Zone.