Active and capable faults (FAC) and buildings in Norcia, interventions carried out and possibile technicolor and regulatory actions.

In Norcia, studies have been carried out to identify active and capable faults, faults for which there is evidence of repeated reactivation in the last 40,000 years and capable of breaking the topographic surface.

The studies have been carried out since 2004 and, over the years, interventions have been carried out on buildings positioned above them before the earthquakes occurred. The 2016 earthquake, which produced surface faulting phenomena, has allowed us to confirm the technical indications on land management drawn up by the Regional Geological Section and the effectiveness of the interventions carried out on the buildings. On the basis of the knowledge possible technical and regulatory actions were then identified. The intervention hypotheses that were developed (1, 2A, 2B, 2C, 2D) required that the designers, geologists and engineers specify the detail of the FAC trace, with respect to the footprint of the building involved, then carrying out a design with any special interventions for the reduction of geological risk, depending on the reconstruction intervention chosen.

1-In the case of availability of land by the owner, there are various possibilities of rebuilding in the same municipality or in another municipality with the relocation of the building accepted, on the owner's proposal.

2-Reconstruction in which the PZI indicates special interventions for the reduction of geological risk, which are approved by the CO and therefore do not require a variation to the urban planning tools.

Special interventions with the adoption of specific seabed techniques capable of resisting the movements of the FAC by means of slabs/double slabs and such as not to induce the breakage of the seabed works.

For the situation of Norcia and the peri-urban areas of the capital, a FAC scheme was defined by hypothesizing a normal fault with a displacement of 30 centimeters and considering, for safety reasons, a 45° inclined plane and not a pseudo-vertical one and therefore with relative horizontal displacements as well.

Interventions can be hypothesized with foundations with a slab with a joint (special intervention A) so that the structure is able to withstand the modification due to the relative movements and the size of the loads; or with foundations resting on a cantilever (special intervention B) only on the upstream side of the FAC or footwall (fault bed), since in these areas they are all normal faults; or with movement of the reconstruction bed which will be a slab (special intervention C); or other special interventions that demonstrate the substantial reduction in geological risk (special intervention D).

Reconstruction interventions with special interventions must not damage nearby buildings considering that there must in any case be a safety distance to avoid interference with nearby buildings equal to the height of the building to be rebuilt; reconstruction astride the FAC with a joint such as to allow movement and therefore the reconstructed building that must be cut to ensure that the possible movement does not damage the foundation slab and nearby buildings.