A detailed examination of the surface dislocations along the main active zones located in sedimentary basins (in particular the Colfiorito fault, the Cesi fault and Colle Croce- Annifo fault) was the main task of this group. According to previous works (Pizzi, 1992; Cello et al., 1997) and field observations, the NW-SE and north-south main active faults coincide with eastern limits of the basins. Active faults appear as bedrock fault scarps in limestones mesozoic formation, with 10 to a few 100 m length of individual fault scarps.
The ongoing study and analysis of surface breaks characteristics which are all located on steep slopes suggest a gravitational origin of movements (sliding of slope deposits). Due to the complexity of earthquake-induced structures and before assessing the definite origin of the surface deformation, dislocations observed along the west side of Mt Tolagna and those across the road La Pintura-Selvapiana need further investigations.
Following the earthquake of 14 October
1997 (Ms 5.5, 15:23 UT) in the area of Sellano (20 km south of Colfiorito),
surface ruptures with a minimum of 2.5 km continuous faulting, cracks and
fissures were formed between Renaro and Mevalle villages. Moreover, and
near Rasenna village, another set of surface faulting can be observed along
0.5 km showing evidence of ruptures across a river-bed.
These new observations show clear and
continuous ruptures with left lateral movements of a few cm to 10 cm of
vertical displacements and up to 9 cm of opened cracks. It is of interest
to mention that faults, fissures and cracks dissect different geological
formations and have no correspondance with any movements on slopes.
Field observations clearly indicate a
tectonic pattern of surface ruptures produced during the 14 October seismic
event. Further investigations will provide a detailed map of surface faulting.
A synthesis of
main observations is reported in the web site of the C.S.
Geologia Tecnica
Last updated:
20/10/1997