Abstract
The Matese and Beneventano areas coincide with the transition from the central to the southern Apennines and are characterized by both SW- and NE-dipping normal faulting seismogenic structures, responsible for the large historical earthquakes. We studied the Matese and Beneventano seismicity by means of high-precision locations of earthquakes spanning from 29 December 2013 to 4 September 2018. Events were located by using all of the available data from temporary and permanent stations in the area and a 1D computed velocity model, inverting the dataset with the Velest code. For events M > 2.8 we used P- and S-waves arrival times of the strong motion stations located in the study area. A constant value of 1.83 for Vp/Vs was computed with a modified Wadati method. The dataset consists of 2378 earthquakes, 18,715 P- and 12,295 S-wave arrival times. We computed 55 new fault plane solutions. The mechanisms show predominantly normal fault movements, with T-axis trends oriented NE–SW. Only relatively small E–W trending clusters in the eastern peripheral zones of the Apenninic belt show right-lateral strike-slip kinematics similar to that observed in the Potenza (1990–1991) and Molise (2002 and 2018) sequences. These belong to transfer zones associated with differential slab retreat of the Adriatic plate subduction beneath the Apennines. The Matese sequence (December 2013–February 2014; main shock Mw 5.0) is the most relevant part of our dataset. Hypocentral depths along the axis of the Apenninic belt are in agreement with previous seismological studies that place most of the earthquakes in the brittle upper crust. We confirm a general deepening of seismicity moving from west to the east along the Apennines. Seismicity depth is controlled by heat-flow, which is lower in the eastern side, thus causing a deeper brittle–ductile transition.
Highlights
An accurate hypocentral determination is an important pre-requisite in seismological investigation and geodynamic interpretation
Considering the established seismotectonic pattern of the southern Apennines extensional belt, we present evidence of three seismic sequences in the Sannio–Matese area, with main shock and aftershock hypocentral depths in agreement with previous seismological studies
We show that the Mw 5.0 29 December 2013 earthquake was nucleated along a NW-striking and SW-dipping normal fault at 12.3 km depth, that borders the southwestern part of the Matese massif
Summary
An accurate hypocentral determination is an important pre-requisite in seismological investigation and geodynamic interpretation. Considering the established seismotectonic pattern of the southern Apennines extensional belt, we present evidence of three seismic sequences in the Sannio–Matese area (central–southern Italy), with main shock and aftershock hypocentral depths in agreement with previous seismological studies. Other faults associated with individual historical earthquakes in the southern Apennines are thought to extend down to 15–16 km of depth, which is commonly the maximum nucleation depth as shown by the moderate to large seismicity in the last 35 years. This observation is consistent with the 15–18 km depth of the brittle–ductile transition (BDT) in the crust beneath the central–southern Apennines [8,9].
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