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The seismogenic structure of the 2013-2014 Matese seismic sequence, Southern Italy:
Implication for the geometry of the Apennines active extensional belt
Ferranti L.1, Milano G.2, Burrato P.3, Palano M.4, Cannavò F.4
1DiSTAR, Università Federico II, Napoli, Italy; lferrant@unina.it
2 INGV, Osservatorio Vesuviano, Napoli, Italy; girolamo.milano@ov.ingv.it
3 INGV, Roma, Italy; pierfrancesco.burrato@ingv.it
4 INGV, Osservatorio Etneo, Catania, Italy; mimmo.palano@ingv.it; flavio.cannavo@ingv.it
Geophys. J. Int. (2015) 201, 823–837
http://www.distar.unina.it/images/ricerca/Fig__7_crustal_model.jpgSeismological, geological and geodetic data have been integrated to characterize the seismogenic structure of the late 2013-early 2014 moderate energy (maximum local magnitude MLmax=4.9) seismic sequence that struck the interior of the Matese Massif, part of the Southern Apennines active extensional belt. The sequence, heralded by a ML=2.7 foreshock, was characterized by two mainshocks with ML=4.9 and ML=4.2, respectively, which occurred at a depth of ~17-18 km. The sequence was confined in the 10-20 km depth range, significantly deeper than the 1997-1998 sequence which occurred few km away on the northeastern side of the massif above ~15 km depth. The depth distribution of the 2013-14 sequence is almost continuous, albeit a deeper (16-19 km) and a shallower (11-15 km) group of events can be distinguished, the former including the mainshocks and the foreshock. The epicentral distribution formed a ~10 km long NNW-SSE trending alignment, which almost parallels the surface trace of late Pliocene- Quaternary southwest-dipping normal faults with a poor evidence of current geologic and geodetic deformation. We built an upper crustal model profile for the eastern Matese massif through integration of geological data, oil exploration well logs and seismic tomographic images. Projection of hypocenters on the profile suggests that the seismogenic volume falls mostly within the crystalline crust and subordinately within the Mesozoic sedimentary cover of Apulia, the underthrust foreland of the Southern Apennines fold and thrust belt. Geological data and the regional macroseismic field of the sequence suggest that the southwest -dipping nodal plane of the mainshocks represents the rupture surface, that we refer to here as the Matese fault. The major lithological discontinuity between crystalline and sedimentary rocks of Apulia likely confined upward the rupture extent of the Matese fault. Repeated co-seismic failure represented by the deeper group of events in the sequence, activated in a passive fashion the overlying ~11-15 km deep section of the upper crustal normal faults. We consider the southwest -dipping Matese fault representative of a poorly known type of seismogenic structures in the Southern Apennines, where extensional seismogenesis and geodetic strain accumulation occur more frequently on NE-dipping, shallower-rooted faults. This is the case of the Boiano Basin fault located on the northern side of the massif, to which the 1997-1998 sequence is related. The close proximity of the two types of seismogenic faults at the Matese Massif is related to the complex crustal architecture generated by the Pliocene-early Pleistocene contractional and transpressional tectonics.
Key-words: Seismicity and tectonics; Continental tectonics: extensional; Crustal structure.