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belt. The basin is bounded to the east by the Gubbio Fault, a W-dipping, normal fault dissecting a large
Jurassic-Oligocene anticline. Although located along one of the main seismogenic zones of the Peninsula, both
historical and instrumental is seismicity is limited with the only exception for the 29 April 1984, Ms 5.3 earthquake,
which occurred about 10 km southwest of the basin. Most of the literature attributes this seismicity
to the Gubbio Fault. New geomorphic and geologic investigations based on field and aerial photo surveys and DEM
analyses provide new insights on the active faulting in the area and are used to infer potential seismogenic sources.
Limited evidence of ongoing deformation along the surface expression of the Gubbio Fault was found, possibly
because of low rates of deformation versus fast erosional processes. The western side of the basin appears to be controlled
by an east-dipping normal fault, antithetic to the Gubbio Fault. Standard dislocation modeling was used to
understand the role played by the Gubbio Fault and its antithetic. The Gubbio Fault was divided into a high-angle section
above 3.5 km and a low-angle section between 3.5 and 6 km depth. Based on different tests we conclude that
both sections of the Gubbio Fault as well as the antitethic fault contributed to the present setting of the basin. At present
the antithetic fault appears to be the most effective in producing a geomorphic signature and controlling the basin
width. The high-angle Gubbio Fault played a major role in the basin growth but now its activity rate appears minor.
Because of the characteristics and location of the 1984 earthquake, the low-angle Gubbio Fault is assumed to be
presently active and seismogenic. Based on the integration of geologic, geomorphic and seismological data we suggest
that the low-angle Gubbio Fault is formed by two individual sources capable of M 5.3-5.9 earthquakes. The
southern source ruptured in the 1984 earthquake while the northern source did not rupture recently nor historically.
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