STRESS PERMUTATIONS, OVERPRESSURE AND STRIKE-SLIP FAULTING DURING TECTONIC INVERSION

 The evolution of stresses during the tectonic cycle, between maximum compressive stress vertical during extension and least compressive stress vertical during contraction, will tend to involve phases when the intermediate compressive stress is vertical, promoting strike-slip deformation. Variations in the relative magnitudes of the stress axes are caused by variations in overburden and tectonic forces. Deformation, including transient strike-slip and inverted normal faults, is preferentially developed in overpressured areas because high fluid pressures promote faulting. Overpressure can develop because of compaction during burial, and as overburden is reduced during uplift and erosion. The evolution of stresses and fluid pressures are illustrated using the Apennines of the Umbria-Marches region of central Italy and the Mesozoic exposures in Somerset, UK.