doi: 10.1111/j.1365-3121.2004.00582.x Growth, interaction and seismogenic potential of coupled active normal faults (Isernia Basin, central-southern Italy)
Daniela Di Bucci,1 Giuseppe Naso,1 Sveva Corrado2 and Igor M. Villa3 1Dipartimento della protezione civile, Servizio Sismico Nazionale, Via Vitorchiano n. 4, 00189 Rome; 2Dipartimento di Scienze Geologiche, Universita` degli Studi ‘Roma tre’, L.go S. L. Murialdo n. 1, 00146 Rome; 3Institut fu¨r Geologie, Universita¨t Bern, 3012 Bern, Switzerland; Dipartimento di Scienze Geologiche e Geotecnologie, Universita` di Milano Bicocca, 20126 Milan, Italy
ABSTRACT
The inception and growth of the active Carpino-Le Piane Basin than 253 ± 22 ka BP, and very probably as recently as <28 ka BP. Fault System (CLPBFS; central-southern Apennines, Italy) was These ages, combined with structural data (geometry and analysed with respect to the neighbouring Isernia and Surround- kinematics of the fault systems), indicate that the inception and ing (ISFS) and Boiano Basin (BBFS) extensional Fault Systems. development of the CLPBFS could be strictly related to the stress 39Ar–40Ar dating showed that the BBFS was already active changes caused by earthquakes occurring on the BBFS. 649 ± 21 ka BP and that the ISFS was active at least 476 ± 10 ka BP, whereas the activity of the CLPBFS started certainly later Terra Nova, 17, 44–55, 2005
Boiano Basin Fault System (BBFS; since Middle Pleistocene (Patacca Introduction Fig. 2). These are distinct fault seg- et al., 1992; Corrado et al., 1997; Fer- The boundary area between the cen- ments both in terms of geometry and ranti, 1997; Porfido et al., 2002). All tral and southern Apennines thrust geology (McCalpin, 1996, and refer- along the axis of the chain, this belt of the Italian peninsula includes ences therein); moreover, according to extension is still active today and the surroundings of Isernia, an some authors (e.g. Porfido et al., responsible for strong earthquakes important town of the Molize region 2002), they host the seismogenic faults (Gruppo di Lavoro CPTI, 1999; Mon- (Fig. 1). Here, a recent study identi- responsible for the 1805 Boiano earth- tone et al., 1999; Galadini and Galli, fied two local intramontane basins as quake mainshock (I0 ¼ X MCS; Gru- 2000; D’Addezio et al., 2001; Roberts half-grabens formed by a 10-km long, ppo di Lavoro CPTI, 1999) and for et al., 2004; Roberts and Michetti, N330 striking and NE dipping set of one of the related strong aftershocks. 2004; Fig. 1). normal faults (Di Bucci et al., 2002; This work aims at showing how the It is widely accepted in literature Figs 2 and 3). The late Holocene growth and interaction of two import- that extension on the BBFS is acting activity of these faults [called Carpi- ant adjacent extensional systems in the since Middle Pleistocene (for instance, no-Le Piane Basins Fault System Apennines, the ISFS and the BBFS, see Corrado et al., 1997; Galli and (CLPBFS); Fig. 4] was constrained led to the formation of new late Galadini, 2003, and references there- for the last 4000 years by analysing UpperPleistocene to Holocene faults in). This age is compatible with the 65 wells drilled on modern fluvio- and associated sub-basins within one tectonic evolution of the Matese Mas- lacustrine deposits that fill the intra- of the said structures (the CLPBFS sif (Calabro` et al., 2003) and derives montane basins. within the ISFS). This is not well from Middle–Upper Pleistocene te- Field data suggest that the CLPBFS understood and can have significant phra deposits filling the Boiano Basin, formed during the Upper Pleistocene– impact on the knowledge of ongoing faulting of Middle Pleistocene tephra Holocene within the northernmost extensional processes and fault link- deposits and Pleistocene slope-scree, part of a regional tectonic depression age, as well as on the associated and offset of Pleistocene remnant N300 oriented, which developed landscape evolution and seismicity in surfaces. However, no 39Ar–40Ar iso- since Middle Pleistocene from the the Apennines. This topic was ad- topic ages were available before the Isernia surroundings to the Sepino dressed by applying structural analysis present work to quantitatively con- Plain, for a length of about 40 km and 39Ar–40Ar technique, which pro- strain the age of this extension. (Corrado et al., 1997; Figs 2 and 3). vided new data and allowed a totally The BBFS is a well-known active We refer to northernmost part of this novel interpretation based on the extensional structure (Cucci et al., depression as the Isernia and Sur- integration of geological data and 1996; Naso et al., 1998; Basili et al., roundings Fault System (ISFS), and physical models of interaction be- 1999; Guerrieri et al., 1999; Blumetti to the adjacent central part as the tween seismogenic sources. et al., 2000; Valensise and Pantosti, 2001; Porfido et al., 2002; Galli and Galadini, 2003; Figs 1 and 2), which Correspondence: Daniela Di Bucci, Structural data Dipartimento della protezione civile, develops with N300 strike for about Servizio Sismico Nazionale, Via Vitorchi- The Quaternary development of the 25–28 km, with a complex extensional ano n. 4, 00189 Rome, Italy. Tel.: +39 06 ISFS, BBFS and CLPBFS is an pattern. This consists of a NE-dipping 6820 4761; e-mail: daniela.dibucci@ expression of the SW–NE extension master fault, which develops down to protezionecivile.it that has been acting in the study area a depth of at least 9 km (Mazzoli
44 2005 Blackwell Publishing Ltd Terra Nova, Vol 17, No. 1, 44–55 D. D. Bucci et al. • Growth and interaction of active normal faults ......
12°30'E 13°30'E 14°30'E 15°30'E 0 20 Bolsena A Lake km G ran PESCARA Sa sso Ra nge 42°20'N L'AQUILA N T iyb e M r a V i a e Adriatic Sea l l l le a
M
t SULMONA . Bracciano S Lake im Fucino 42°00'N b ru Basin in i M ts M a rs ROME ica Al to Mo lise Gargano Promontory 41°40'N Figs 2 and 3 ISERNIA Tyrrhenian Sea CAMPOBASSO Vo lsc i M ts Matese Mts
Sa nn io
Marine and continental clastic deposits Carbonate platform Synorogenic hemipelagic and (Pliocene-Quaternary) (Trias-Miocene) turbiditic sequences (Tortonian-Pliocene) Volcanic deposits Slope and by-pass margin deposits (Pleistocene) (Lias-Miocene) Thrusts Clayey-carbonate and arenaceous turbidites Molise-Sannio pelagic basin (Cretaceous-Eocene) (Oligocene-Miocene) Faults
Pescara B Viterbo Rieti
L'Aquila N 0 km 50 Central Apennines Rome
Isernia 1805 Campobasso Southern Magnitude scale Apennines >7.0 7.0–6.8 6.8–66.4 6.4–66.0 6.0–65.6 5.6–65.2 Benevento
Fig. 1 (A) Geological map of the central-southern Apennines (after Di Bucci et al., 2002, modified). (B) Largest earthquakes of the central-southern Apennines (data after Boschi et al., 1997, and Valensise and Pantosti, 2001). The size of the square symbols is proportional to an ‘equivalent magnitude’ (Me) derived from intensity data. et al., 2000; Butler et al., 2004), and of An example comes from S. Giorgio site gave us the possibility to quanti- synthetic and antithetic Quaternary area (Fig. 5), where normal faults tatively constrain the Middle Pleisto- normal faults linked by shallow, pre- affect a succession of Pleistocene la- cene tectonic activity of the BBFS. Quaternary, mainly E–W-oriented custrine and pyroclastic sediments This fault system strictly coincides high-angle faults, reactivated by the (samples San2 and San3) forming a with that revealed by drainage net- present-day extensional stress field terrace along the main slope of the work studies (Cucci et al., 1996) and (Fig. 3, plots G–M). BBFS (Brancaccio et al., 1979). This with the seismogenic fault inferred