Palaeoseismological constraints on the Anghiari normal fault (Northern Apennines, Italy): first results.

The Italian Apennines is a slowly deforming area, despite not properly being an intraplate region. This is particularly true for the Northern Apennines, where<= 2mm/yr of extension is accommodated by low-slip rate normal faults, often organized in parallel systems partitioning the regional deformation. As a result, large earthquakes on individual faults are separated by long (>~1ka) recurrence intervals. This makes earthquake geology a fundamental tool for characterizing the seismic hazard.

The Anghiari fault is a 11 km-long segmented NE-dipping normal fault bounding the western side of the Upper Tiber Valley (Northern Apennines, Italy), and belonging to the well-known Altotiberina low-angle normal fault system. Here, we provide unprecedented evidence of the Holocene activity of the Anghiari fault through geological, geophysical and palaeoseismological investigations.

The fault is composed of at least two nearly parallel splays. One splay runs at the base of the Pleistocene Anghiari ridge, downfaulting the late Quaternary alluvial deposits of the Tiber Valley against Middle Pleistocene continental deposits. The other splay is located within the Middle Pleistocene units of the Anghiari ridge. We focus on the latter.
Detailed geomorphological analysis, geological mapping and near-surface geophysics, enabled us to select two sites for palaeoseismological trenching. Radiocarbon dating of faulted sediments provides constraints for late Holocene and historical surface faulting events significantly contributing to the estimation of the seismic hazard in the region.