Abstract
We studied in detail the Gioia Sannitica active normal fault (GF) along the Southern Matese Fault system in the southern Apennines of Italy. The current activity of the fault system and its potential to produce strong earthquakes have been underestimated so far, and are now defined. Precise mapping of the GF fault trace on a 1 : 20,000 geological map and several point data on geometry, kinematics and throw rate are made available in electronic format. The GF, and in general the entire fault system along the southern Matese mountain front, is made of slowly-slipping faults, with a long active history revealed by the large geologic offsets, mature geomorphology, and complex fault pattern and kinematics. Present activity has resulted in Late Quaternary fault scarps resurrecting the foot of the mountain front, and Holocene surface faulting. The slip rate varies along-strike, with maximum Late Pleistocene – Holocene throw rate of ~0.5 mm/yr. Activation of the 11.5 km-long GF can produce up to M 6.1 earthquakes. If activated together with the 18 km-long Ailano-Piedimonte Matese fault (APMF), the seismogenic potential would be M 6.8. The slip history of the two faults is compatible with a contemporaneous rupture. The observed Holocene displacements on the GF and APMF are compatible with activations during some poorly known historical earthquakes, such as the 1293 (M 5.8), 1349 (M 6.8; southern prolongation of the rupture on the Aquae Iuliae fault?) and CE 346 earthquakes. A fault rupture during the 847 poorly-constrained historical earthquake is also compatible with the dated displacements.
Highlights
Detailed field mapping of active faulting is essential for populating fault databases oriented at mitigating the seismic risk from 30 ground shaking and fault displacement hazard
We studied in detail the Gioia Sannitica active normal fault (GF) along the Southern Matese Fault system in the 15 southern Apennines of Italy
The observed Holocene displacements on the Gioia Sannitica normal fault (GF) and Ailano-Piedimonte Matese fault (APMF) are compatible with activations during some poorly known historical 25 earthquakes, such as the 1293 (M 5.8), 1349 (M 6.8; southern prolongation of the rupture on the Aquae Iuliae fault?) and CE 346 earthquakes
Summary
The 2016 earthquakes demonstrate that the geology of active faults is as critical as historical seismicity for estimating the true seismic potential in areas characterized by low strain rates (velocities of a few mm/yr) and long return periods of strong earthquakes (≥ M 6.5), such as the Italian 45 Apennines. This has implications in seismic hazard assessments (e.g., Valentini et al, 2019). The data and observations of active faulting along the Gioia Sannitica normal fault are combined with new and pre-existing data from the northern part of the system and discussed together in terms of overall seismogenic potential of the Southern Matese Fault system
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