Normal faulting, transcrustal permeability and seismogenesis in the Apennines (Italy)

Late Pliocene-Pleistocene tectonic evolution of the Apennines is driven by progressive eastward migration of extensional downfaulting superposed onto the Late Miocene-Early Pliocene compressional thrust belt. This process has led to distinct structural domains that show decreasing transcrustal permeability from conditions of pervasive mixing between deep and surface fluids in the hinterland (west) to conditions of restricted fluid circulation and overpressuring in the foreland (east). At present, the highest rates of normal faulting and the strongest seismicity occur in the area bounded by stretched, highly permeable crust to the west and thick, poorly permeable crust to the east. In this area, the seismogenic sources of the largest earthquakes (5 < M-s < 7) are potentially related to mature normal faults that deeply penetrate thick brittle upper crust, and act as transient high-permeability channels during seismic activity. In this framework, it is plausible that domains of overpressuring govern progressive inception of normal faulting and fluid redistribution in the crust, leading to eastward migration of the belt of maximum seismicity with time. (C) 2002 Elsevier Science B.V. All rights reserved.