The 2013–2018 Matese and Beneventano Seismic Sequences (Central–Southern Apennines): New Constraints on the Hypocentral Depth Determination

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.

First-Motion Focal Mechanism Solutions for 2015–2019 M ≥ 4.0 Italian Earthquakes

“…Sharing the hypocenter depths, source mechanisms, fault orientations, and structural features, the Montecilfone 2018 and Molise 2002 sequences can be considered both expressions of a distinct seismotectonic setting characterizing that wide region of southern Italy extending between the Apennine external zone and the Apulian foreland. Our finding, together with minor deep swarms with dominant strike-slip focal solutions that occurred in recent years (Trionfera et al, 2020), reinforce indeed previous seismotectonic models that emphasize the role of pre-existing W-E trending lithospheric shear zones in accommodating the Adria intraplate deformation in response to Africa-Eurasia plate convergence (Di Bucci et al, 2010) and in producing moderate to strong deep earthquakes in the Adriatic side of the southern Apennines (Fracassi et al, 2004;Valensise et al, 2004).…”

An updated view of the Italian seismicity from probabilistic location in 3D velocity models: The 1981–2018 Italian catalog of absolute earthquake locations (CLASS)

“…Here we find a wide area where up to 80% (orange to red tones) of the thick Adriatic crust is involved in fragile deformation. This evidence is probably related to the peculiar seismotectonics of this area, where several models suggests the presence of pre-existing W-E trending deep strike-slip seismogenic sources, accommodating the Adriatic intraplate deformation inducing moderateto-strong deep earthquakes (see Fracassi et al, 2004;Valensise et al, 2004;Latorre et al, 2010;Trionfera et al, 2020;Ciaccio et al, 2021 among many others).…”

The Attenuation and Scattering Signature of Fluid Reservoirs and Tectonic Interactions in the Central‐Southern Apennines (Italy)

“…MuRAT also requires seismic velocities for tracing rays. However, no unique 3D velocity model exists for the area: we thus use as a reference the 1D model (Table S1 in Supporting Information S1) from Trionfera et al (2019) extended over a grid spaced about 10 (horizontal) and 5 km (vertical).…”