Late Quaternary faulting in the southern Matese (Italy): implications for earthquake potential and slip rate variability in the southern Apennines

Abstract

Abstract. We studied the Gioia Sannitica active normal fault (GF) along the southern Matese fault (SMF) system in the southern Apennines of Italy in detail. The current activity of the fault system and its potential to produce strong earthquakes have been underestimated so far and are now defined here. Precise mapping of the GF fault trace on a 1:20 000 geological map and point and line data on the geometry, kinematics, and slip rate of the faults forming the SMF system are made available in electronic format. The GF, and the entire fault system along the southern Matese mountain front in general, is made of slowly slipping faults with a long active history revealed by the large geologic offsets, mature geomorphology, and complex fault patterns and kinematics. Present activity has resulted in late Quaternary fault scarps resurrecting the foot of the mountain front and Holocene surface faulting. The resurrected mountain front indicates variation in slip rate through time. The slip rate varies along-strike, with a maximum Upper Pleistocene–Holocene slip rate of ∼ 0.5 mm yr−1. Activation of the 11.5 km long GF can produce up to M 6.2 earthquakes. If activated together with the 18.5 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 constrained historical earthquakes, such as the 1293 (M 5.8), 1349 (M 6.8; possibly a southern prolongation of the rupture on the Aquae Iuliae fault), and 346 CE earthquakes. A fault rupture during the poorly constrained 847 CE earthquake is also chronologically compatible with the dated displacements.