Strike-slip geometry inferred from the seismicity of the Northern-Central

The aim of this paper is to draw attention to the real number and distribution of strike-slip earthquake
focal mechanisms that are displayed in the recent seismicity of the Northern-Central Apennines. Their
relation to the superficial normal fault plane solutions and thrust front along the Eastern side of the
Apenninic chain can be described by a geometrical model (Riedel-System, also Riedel shear model). First
we define three sectors characterized by their different seismological signatures: the North-Western
Sector (NWS), the Western Central Sector (WCS) and the Eastern Central Sector (ECS). These three blocks,
according to the available data, act independently from each other as a consequence of interaction among
themselves, the forces induced by plate tectonics in the Mediterranean area and the blocking effect of
the Alpine Chain, leading to an increased amount of transpressional, pure strike-slip and transtensional
tectonics below 10 km depth.

Aki, K., Richards, P.G., 1980. Quantitative Seismology. Freeman and Co., New York.
Anderson, H., Jackson, J., 1987. Active tectonics of the adriatic region. Geophys. J.
Roy. Astron. Soc. 91, 937–983.
Bagh, S., Chiaraluce, L., De Gori, P., Moretti, M., Govoni, A., Chiarabba, C., Di Bartolomeo,
P., Romanelli, M., 2007. Background seismicity in the Central Apennines
of Italy: the Abruzzo region case study. Tectonophysics 444 (1–4), 80–92.
Bigi, G., Casentino, D., Parlotto, M., Sartori, R., Scandone, P., 1990. Structural model
of Italy. Sheets 1, 2, 3 and 4, PFG-CNR. Quad. Ric. Sci., S.EL.CA., Florence, Scale
1:500.000.
Boccaletti M. and Coli M, 1982. Carta strutturale dell’Appennino Settentrionale. CNR,
Progetto Finalizzato Geodinamica, 5 – Modello strutturale 1:250.000.
Bonini, M., 1998. Chronology of deformation and analogue modelling of the
Plio-Pleistocene ‘Tiber Basin’: implications for the evolution of the Northern
Apennines (Italy). Tectonophysics 285, 147–165.
Bortolotti, V., 1966. La tettonica trasversale dell’Appennino I-La linea Livorno-Sillaro.
Boll. Soc. Geol. Ital. 85, 529–540.
Calamita, F., Paltrinieri, W., Esestime, P., Viandante, M.G., 2006. Assetto strutturale
crostale dell’appennino centro-meridionale. Rend. Soc. Geol. It., Nuova Serie 2,
103–107.
Calamita, F., Esestime, P., Paltrinieri, W., Scisciani, V., Tavarnelli, E., 2009. Structural
inheritance of pre-and syn-orogenic normal faults on the arcuate geometry
of Pliocene-Quaternary thrust: examples from Central and Southern Apennine
Chain. Ital. J. Geosci. 128, 381–394.
Cattaneo, M., Augliera, P., De Luca, G., Gorini, A., Govoni, A., Marcucci, S., Michelini,
A., Monachesi, G., Spallarossa, D., Troiani, L., 2000. XGUMS the 1997 Umbria-
Marche (Italy) earthquake sequence: analysis of the data recorded by the local
and temporary networks. J. Seismol. 4, 401–414.
Cello, G., Mazzoli, S., Tondi, E., Turco, E., 1997. Active tectonics in the central Apennines
and possible implications for seismic hazard analysis in peninsular Italy.
Tectonophysics 272, 43–68.
Cerrina Feroni, A., Otaria, G., Martinelli, P., Martelli, L., Catanzariti, R., 2002. Carta
Geologico-Strutturale dell’Appennino Emiliano-Romagnolo. Sheet 1, S.E.L.CA.,
Firenze, Scale 1:250.000.
Cerrina Feroni, A., Otaria, G., Ellero, A., 2004. In: Crescenti, V., D’Offizi, S., Merlino,
S., Sacchi, L. (Eds.), The Northern Apennine, Italy: Geological Structure and
Traspressive Evolution. Special Volume of the Ital. Geol. Soc., IGC 32 Florence.,
pp. 15–32.
Chiarabba, C., Covane, L., Di Stefano, R., 2005. A new view of Italian seismicity using
20 years of instrumental recordings. Tectonophysics 395, 251–268.
Coltorti, M., Farabolini, P., Gentili, B., Pambianchi, G., 1996. Geomorphological evidence
for anti-Apennine faults in the Umbro-Marchean Apennines and in the
peri-Adriatic basin, Italy. Geomorphology 15, 33–45.
Cunningham, W.D., Mann, P., 2007. In: Cunningham, W.D., Mann, P. (Eds.), Tectonics
of strike-slip restraining and releasing bends. Tectonics of strike-slip restraining
and releasing bends. Geol. Soc. Lond. Spec. Publ. 290, 1–12.
D’Agostino, N.D., Avallone, A., Cheloni, D., D’Anastasio, E., Mantenuto, S., Selvaggi,
G., 2008. Active tectonics of the Adriatic region from GPS and earthquake slip
vectors. J. Geophys. Res. doi:10.1029/2008jb005860.
Daly, M.C., 1986. Crustal shear zones and thrust belts: their geometry and continuity
in Central Africa. Phil. Trans. R. Soc. Lond. 317A, 11–128.
Davis, G.H., Reynolds, S.J., 1996. Structural Geology of Rocks and Regions, 2nd ed.
John Wiley & Sons, Inc., New York, ISBN 0-471-52621-5, 776p.
De Alteriis, G., 1995. Different foreland basins in Italy: examples from the central
and southern Adriatic Sea. Tectonophysics 252, 349–373.
De Luca, G., Scarpa, R., Filippi, L., Gorini, A., Marcucci, S., Marsan, P., Milana, G., Zambonelli,
E., 2009. A detailed analysis of two Seismic Sequences in Abruzzo, Central
Apennines, Italy. J. Seismol. 4, 1–21.Dellisanti, F., Pini, G.A., Tateo, F., Baudin, F., 2008. The role of tectonic shear strain on
the il-litization mechanism of mixed-layers illite–smectite. A case study from a
fault zone in the Northern Apennines, Italy. Int. J. Earth Sci. 97, 601–616.
Devoti, R., Riguzzi, F., Cuffaro, M., Doglioni, C., 2008. New GPS constraints on the
kinematics of the Apennines subduction. Earth Planet. Sci. Lett. 273, 163–174.
Di Luzio, E., Saroli, M., Esposito, C., Bianchi-Fasani, G., Cabinato, G.P., Scarascia-
Mugnozza, G., 2004. Influence of structural framework on mountain slope
deformation in the Maiella anticline (Central Apennines Italy). Geomorphology
60, 417–432.
Ekström, G., Morelli, A., Boschi, E., Dziewonski, A.M., 1998. Moment tensor analysis
of the Central Italy earthquake sequence of September–October 1997. Geophys.
Res. Lett. 25, 1971–1974.
Elter, P., Giglia, G., Tongiorgi, M., Trevisan, L., 1975. Tensional and compressional
areas in the recent (Tortonian to Present) evolution of the Northern Apennines.
Boll. Geofis. Teor. Appl. 17, 3–18.
Eva, E., Ferretti, G., Solarino, S., 2005. Superposition of different stress orientations
in the western sector of the northern Apennines (Italy). J. Seismol. 9, 413–430.
Favali, P., Funiciello, R., Mattietti, G., Mele, G., Salvini, F., 1993. An active margin
across the Adriatic Sea (central Mediterranean Sea). Tectonophysics 219,
109–117.
Fazzini, P., Gelmini, R., 1982. Tettonica trasversale nell’Appennino Settentrionale.
Mem. Soc. Geol. Ital. 24, 299–309.
Ferranti, L., Oldow, J.S., Sacchi, M., 1996. Pre-Quaternary orogen-parallel extension
in the Southern Apennine belt, Italy. Tectonophysics 260, 325–347.
Frepoli, A., Amato, A., 1997. Contemporaneous extension and compression in the
Northern Apennines from earthquake fault-plane solutions. Geophys. J. Int. 129,
368–388.
Frepoli, A., Amato, A., 2000. Fault plane solutions of crustal earthquakes in Southern
Italy (1988–1995): seismotectonic implications. Annali di Geofisica 43, 437–467.
Galadini, F., Messina, P., 2001. Plio-Quaternary changes of normal fault architecture
in the Central Apennines (Italy). Geodin. Acta 14, 321–344.
Gasparini, C., Iannaccone, G., Scarpa, R., 1985. Fault-plane solutions and seismicity
of the Italian Peninsula. Tectonophysics 117, 59–78.
Legg, M.R., Goldfinger, C., Kamerling, M.J., Chaytor, J.D., Einstein, D.E., 2007. In:
Cunningham, W.D., Mann, P. (Eds.), Morphology, Structure and Evolution of
California Continental Borderland Restraining Bends Tectonics of Strike-Slip
Restraining and Releasing Bends, 290. Geol. Soc. Lond. Spec. Publ., pp. 143–168.
Mantovani, E., Babbucci, D., Tamburelli, C., Viti, M., 2009. A review on the driving
mechanism of the Tyrrhenian-Apennines system: implications for the present
seismotectonic setting in the Central-Northern Apennines. Tectonophysics 476,
22–40.
Martini, P.I., Sagri, M., Colella, A., 2001. Neogene-quaternary basins of the inner
Apennines and Calabrian arc. In: Vai, G.B., Martini, P.I. (Eds.), Anatomy of an
Orogen: The Apennines and Adjacent Mediterranean Basins. Kluwer Academic
publisher, pp. 375–400.
Patacca, E., Sartori, R., Scandone, P., 1990. Tyrrhenian basin and Apenninic arc: kinematic
relations since Late Tortonian times. Mem. Soc. Geol. It. 45, 425–451.
Piccardi, L., Gaudemer, Y., Tapponnier, P., Boccaletti, M., 1999. Active oblique extension
in the central Apennines (Italy): evidence from the Fucino region. Geophys.
J. Int. 139, 499–530.
Piccardi, L., Tondi, G., Cello, G., 2006. Geo-structural evidence for active oblique
extension in South-Central Italy. In: Pinter, N., Grenerczy, G., Weber, J., Stein, S.,
Medak, D. (Eds.), The Adria microplate: GPS geodesy, tectonics and Hazard. NATO
Science Series IV-Earth and Environmental Sciences, 61. Springer, pp. p.95–108.
Pino, N.A., Mazza, S., 2000. The Umbria-Marche (Central Italy) earthquakes: relation
between rupture directivity and sequence evolution for the Mw > 5 shocks. J.
Seismol. 4, 451–461.
Pizzi, A. and Galadini, F., 2009. Pre-existing cross-structures and active fault
segmentation in the northern-central Apennines (Italy). Tectonophysics
doi:10.1016/j.tecto.2009.03.018.
Pondrelli, S., Morelli, A., Ekström, G., Mazza, S., Boschi, E., Dziewonski, A.M., 2002.
European–Mediterranean regional centroid-moment tensors: 1997–2000. Phys.
Earth Planet. Int. 130, 71–101.
Pondrelli, S., Morelli, A., Ekström, G., 2004. European–Mediterranean regional centroid
moment tensor catalog: solutions for years 2001 and 2002. Phys. Earth
Planet. Int. 145, 127–147.
Pondrelli, S., Salimbeni, S., Ekström, G., Morelli, A., Gasperini, P., Vannucci, G., 2006.
The Italian CMT dataset from 1977 to the present. Phys. Earth Planet. Int. 159
(3-4), 286–303.
Pondrelli, S., Salimbeni, S., Morelli, A., Ekström, G., Boschi, E., 2007.
European–Mediterranean regional centroid moment tensor catalog: solutions
for years 2003 and 2004. Phys. Earth Planet. Int. 164, 90–112.
Reasenberg, P., Oppenheimer, D., 1985. FPFIT FPPLOT and FPPAGE: FORTRAN computer
programs for calculating and displaying earthquake fault-plane solutions.
USGS Open file Report, 85–739.
Sani, F., Bonini, M., Piccardi, L., Vannucci, G., Delle Donne, D., Benvenuti,
M., Moratti, G., Corti, G., Montanari, D., Sedda, L., Tanini, C., 2009. Late
Pliocene-Quaternary evolution of outermost hinterland basins of the Northern
Apennines (Italy), and their relevance to active tectonics. Tectonophysics
doi:10.1016/j.tecto.2008.12.012.
Sibson, R.H., 1986. In: Das, S., Boatwright, J., Sholz, C.H. (Eds.), Rupture interaction
with fault jogs. Earthquake source mechanics. Geophys. Monogr., 157–167.
Solarino, S., Cassinis, S., 2007. Seismicity of the upper lithosphere and its relationships
with the crust in the Italian region. Boll. Geofis. Teor. Appl. 48, 99–114.
Vezzani, L., Festa, A., Ghisetti, F., 2009. Geological-Structural Map of the Central-
Southern Apennines (Italy). Sheets 1 and 2, S.EL.CA., Florence, Scale 1:250.000.
ISBN 978-88-902635r-r9-0.
Viti, M., Mantovani, E., Babbucci, D., Tamburelli, C., 2011. Plate kinematics
and geodynamics in the Central Mediterranean. J. Geod., 51, 190–204, doi:
10.1016/j.jog.2010.02.006