Active faulting and deep-seated gravitational slope deformation in
carbonate rocks (central Apennines, Italy): a new “close-up” view
Active faulting and Deep-seated Gravitational Slope Deformation (DGSD)
constitute common geological hazards in mountain belts worldwide. In the
Italian central Apennines, km-thick carbonate sedimentary sequences are
cut by major active normal faults which shape the landscape generating
intermontane basins. Geomorphological observations suggest that the
DGSDs are commonly located in the fault footwalls.
We selected five mountain slopes affected by DGSD and exposing the
footwall of active seismic normal faults exhumed from 2 to 0.5 km depth.
We combined field structural analysis of the slopes with microstructural
investigation of the slipping zones from the slip surfaces of both DGSDs
and major faults. The collected data show that DGSDs exploit
pre-existing surfaces formed both at depth and near the ground surface
by tectonic faulting and, locally, by gravitational collapse. At the
microscale, the widespread compaction of micro-grains (e.g., clasts
indentation) forming the cataclastic matrix of both normal faults and
DGSDs is consistent with clast fragmentation, fluid-infiltration and
congruent pressure-solution mechanisms active at low ambient
temperatures and lithostatic pressures. These processes are more
developed in the slipping zones of normal faults because of the larger
We conclude that in carbonate rocks of the central Apennines, DGSDs
commonly exploit pre-existing tectonic faults/fractures and, in
addition, localize slip along newly formed fractures that accommodate
deformation mechanisms similar to those associated to tectonic faulting.
Furthermore, the exposure of sharp slip surfaces along mountain slopes
in the central Apennines can result from both surface seismic rupturing
and DGSD or by a combination of them.