Three-dimensional earthquake locations and upper crustal structure of the Sannio-Matese region (southern Italy)

Abstract
The Sannio-Matese region is one of the most seismically active regions of Italy and has been struck by large historical
earthquakes. At present, the area is characterized by low magnitude background seismicity and small seismic sequences
following Mf4 main events. In this paper, we show Vp and Vp/Vs models and 3D locations for a complete set of earthquakes
occurring in the period 1991–2001. We observe a significant crustal heterogeneity, with large scale east-verging high Vp faultrelated-
folds, stacked by the Pliocene compression. The relocated earthquakes cluster along a 70j east-dipping, NW-striking
plane located at the border of the high Vp thrust units. Normal fault earthquakes related to the young and active extension occur
within these high Vp zones, interpreted as high strength material. We expect large future earthquakes to occur within these high
Vp zones actually characterized by low magnitude seismicity at their borders.
D 2004 Elsevier B.V. All rights reserved.

Alessio, G., Gorini, A., Vilardo, G., Iannaccone, G., 1996. Low
energy sequences in areas with high seismic potential: Benevento
(Sourthern Apennines), April 1990. In: Schenk, V.
(Ed.), Advances in Natural and Technological Hazard Research-
Earthquake Hazard and Risk. Kluwer Academic Publishing,
Dordrecht, pp. 3 –16.
Amato, A., Chiarabba, C., Malagnini, L., Selvaggi, G., 1992.
Three-dimensional P-velocity structure in the region of the
Ms = 6.9 Irpinia, Italy, normal faulting earthquake. Phys. Earth
Planet Inter. 75, 111– 119.
Amato, A., Montone, P., Cesaro, M., 1995. State of stress in southern
Italy from borehole breakouts and focal mechanism data.
Geophys. Res. Lett. 22, 3119– 3122.
Bally, A.W., Burbi, L., Cooper, C., Ghelardoni, R., 1986. Balanced
sections and seismic reflection profiles across the Central Apennines.
Mem. Soc. Geol. Ital. 35, 257–310.
Boschi, E., Ferrari, G., Gasperini, P., Guidoboni, E., Smiriglio, G.,
Valensise, G. (Eds.), 1995. Catalogo Dei Forti Terremoti in Italia
Dal 461 a.c. al 1980. ING-SGA, Bologna. 970 pp.
Chiappini, M., Meloni, A., Boschi, E., Faggioni, O., Beverini, N.,
Carmisciano, C., Marson, I., 2000. Shaded relief magnetic
anomaly map of Italy and surrounding marine areas. Ann. Geofis.
43, 983– 989.
Chiarabba, C., Amato, A., 1997. Upper-crustal structure of the
Benevento area (southern Italy): fault heterogeneities and potential
for large earthquakes. Geophys. J. Int. 130, 229– 239.
Chiarabba, C., Amato, A., 2003. Vp and Vp/Vsimages in the Mw
6.0 Colfiorito fault region (central Italy): a contribution to the
understanding of seismotectonic and seismogenic processes.
J. Geophys. Res. 108 (B5) (10.1029/2001JB001665).
Ciaranfi, N., Guida, M., Iaccarino, G., Pescatore, T., Pieri, P.,
Rapisardi, L., Ricchetti, G., Sgrosso, I., Torre, M., Toriorici,
E., Turco, E., Scarpa, R., Cuscito, M., Guerra, I., Iannaccone,
G.F., Panza, G.F., Scandone, P., 1983. Seismotectonic elements
of the Southern Apennines. Boll. Soc. Geol. Ital. 102 (2–3),
201–222.
Cocco, M., Pacor, F., 1993. The rupture process of the 1980, Irpinia,
Italy earthquake from the inversion of strong motion waveforms.
Tectonophysics 218, 157–177.
Di Bucci, D., Corrado, S., Naso, G., 2002. Active faults at the
boundary between Central and Southern Apennines (Isernia,
Italy). Tectonophysics 359, 47– 63.
Eberhart-Phillips, D., 1986. Three-dimensional velocity structure
in the Northern California Coast Ranges from inversion of
local earthquake arrival times. Bull. Seismol. Soc. Am. 76,
1025– 1052.
Eberhart-Phillips, D., Reyners, M., 1997. Continental subduction
and three-dimensional crustal structure: the Northern South Island
New Zealand. J. Geophys. Res. 102 (B6), 11843– 11861.
Foxall, W., Michelini, A., McEvilly, T.V., 1993. Earthquake travel
time tomography of Southern Santa Cruz Mountains: control of
fault heterogeneity of the San Andrea fault zone. J. Geophys.
Res. 98, 17691– 17710.
Gasparini, C., Iannaccone, G., Scarpa, R., 1985. Fault plane solutions
and seismicity of the Italian peninsula. Tectonophysics
117, 59– 78.
Iannaccone, G., Improta, L., Capuano, P., Zollo, A., Biella, G., De
Franco, R., Deschamps, A., Cocco, M., Mirabile, L., Romeo, R.,
1998. A P-wave velocity model of the upper crust of the Sannio
region (Southern Apennines, Italy). Ann. Geofis. 41, 567– 582.
Improta, L., Iannaccone, G., Capuano, P., Zollo, A., Scandone, P.,
2000. Inferences on the upper crustal structure of Southern
Apennines (Italy) from seismic refraction investigations and
subsurface data. Tectonophysics 317, 273– 297.
Menke, W., 1989. Geophysical data analysis: discrete inverse theory.
Int. Geophys. Ser., vol. 45. Academic Press, San Diego,
CA, pp. 7– 288.
Michael, A.J., Eberhart-Phillips, D., 1991. Relations among fault
behavior, subsurface geology, and three-dimensional velocity
models. Science 253 (5020), 651– 654.
Michelini, A., McEvilly, T.V., 1991. Seismological studies at Parkfield.
Simultaneous inversion for velocity structure and hypocenters
using cubic b-splines parameterization. Bull. Seismol.
Soc. Am. 81, 524–552.
Milano, G., Di Giovambattista, R., Alessio, G., 1999. Earthquakes
swarms in the Southern Apennines chain (Italy): the 1997 seismic
sequence in the Sannio-Matese mountains. Tectonophysics
306, 57– 58.
Milano, G., Ventura, G., Di Giovambattista, R., 2002. Seismic
evidence of longitudinal extension in the Southern Appennines
chain (Italy): the 1997–1998 Sannio-Matese seismic sequence.
Geophys Res. Lett., 29, 20, 2004, 65-1 65-4.
Mostardini, F., Merlini, S., 1986. Appennino centro meridionale:
sezioni geologiche e proposta di modello strutturale. Mem. Soc.
Geol. Ital. 35, 177–202.
Patacca, E., Scandone, P., 1989. Post-Tortonian mountain building
in the Apennines. The role of the passive sinking of a relic
lithospheric slab. In: Boriani, A., Bonafede, M., Piccardo,
G.B., Vai, G.B. (Eds.), The Lithosphere in Italy. Accad. Naz.
Lincei, vol. 80, pp. 157–176.
Roure, F., Casero, P., Vially, R., 1991. Growth processes and melange
formation in the Southern Apennines accretionary wedge.
Earth Planet. Sci. Lett. 102 (3– 4), 395–412.
Thurber, C.H., 1983. Earthquake locations and three-dimensional
crustal structure in the Coyote Lake area, Central California.
J. Geophys. Res. 88, 8226– 8236.
Thurber, C.H., Atre, S.R., Eberhart-Phillips, D., 1995. Three-di-
L. Bisio et al. / Tectonophysics 385 (2004) 121–136 135
mensional Vp and Vp/Vs structure at Loma Prieta, California,
from local earthquake tomography. Geophys. Res. Lett. 22,
3079–3082.
Toomey, D.R., Foulger, G.R., 1989. Tomographic inversion of local
earthquake data from the Hengill-Grensdalur central volcano
complex. J. Geophys. Res. 94, 17487–17510.
Um, J., Thurber, C., 1987. A fast algorithm for two-point seismic
ray tracing. Bull. Seismol. Soc. Am. 77, 972–986.
Valensise, G., Pantosti, D., 2001. The investigation of potential
earthquake sources in peninsular Italy: a review. J. Seismol. 5,
287– 306.
Zhao, D., Kanamori, H., 1993. The 1992 Landers earthquake sequence:
earthquake occurrence and structural heterogeneities.
Geophys. Res. Lett. 20, 1083– 1086.
Zhao, D., Kanamori, H., 1995. The 1994 Northridge earthquake:
3-D crustal structure in the rupture zone and its relation to
the aftershock locations and mechanisms. Geophys. Res. Lett.
22, 763– 766.
Zhao, D., Negishi, H., 1998. The 1995 Kobe earthquake; seismic
image of the source zone and its implications for the rupture
nucleation. J. Geophys. Res., B 103 (5), 9967– 9986.