Cataclastic faults along the SEMP fault system (Eastern Alps, Austria) - a contribution to fault zone evolution, internal structure and paleo-stresses

In this study three different sites along the ENE-trending, sinistral Salzach–Ennstal–Mariazell–Puchberg [SEMP] fault zone were investigated with respect to brittle fault zone evolution and fault re-activation. All sites crop out in Triassic carbonates (Ladinian Wetterstein limestone/–dolomite). Simultaneously (re-) activated faults were investigated with focus on fault-slip data and structural inventory of each individual fault zone.

Configuration of (internal) structural elements, fault core thickness, strike direction and slip sense in addition to particle analysis of fault core cataclasites add up to three different fault types (Fault Types I, II and III).

Fault Type I is classified by a complex internal fault core structure with thicknesses up to several 10s of meters and generally evolve in a strike direction of maximum shear stress (τmax). Type II faults, characterized by cataclastic fault cores with thicknesses up to 1 m, as well as Type III faults (thin solitary cataclastic layers) evolve sub-parallel to the main fault direction and in orientation according to R, R' or X shear fractures with variable (σn/τ) ratio. Progressive development from Type III to Type II and Type I faults is consistent with increasing displacement and increasing fault core width.

Fault type classification and related paleostress analysis provide evidence from field observation compared to theoretical and analog models of Mohr–Coulomb fracture evolution.