Active faulting and seismicity along the Siculo–Calabrian Rift Zone (Southern Italy)

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Tectonophysics 453 (2008) 177 – 192 www.elsevier.com/locate/tecto

Active faulting and seismicity along the Siculo–Calabrian Rift Zone (Southern Italy) S. Catalano, G. De Guidi, C. Monaco, G. Tortorici, L. Tortorici ⁎ Dipartimento di Scienze Geologiche, Università degli Studi di Catania, Corso Italia, 55, 95129 Catania, Italy Received 10 October 2006; accepted 24 May 2007 Available online 14 February 2008

Abstract Southern Italy is dominated by extensional tectonics that in the Calabrian arc and Eastern Sicily produced the development of the Siculo– Calabrian Rift Zone (SCRZ). This zone is represented by a ≈370 km-long fault belt consisting of 10 to 50 km long distinct fault segments which extend both offshore and on land being also responsible of the crustal seismicity of this region. The geological and morphological observations indicate that the active normal faults of the SCRZ are characterized by throw-rates ranging from 0.7 to 3.1 mm/a. They accommodate an almost uniform horizontal extension-rate of about 3.0 mm/a along a WNW–ESE regional extension direction. Based on our field observations and following empirical relationships between magnitude and surface rupture length connections between large crustal earthquakes and distinct fault segments of the SCRZ have been also tentatively tested. Our data indicate moreover that the magnitudes (M) of the historical and instrumental earthquakes are consistent with the estimated values and that the geometry and kinematics of the fault segments and the related different crustal features of the SCRZ control the different seismic behaviours of adjacent portions of the active rift zone. © 2008 Elsevier B.V. All rights reserved. Keywords: Seismotectonics; Quaternary; Normal faulting; Seismicity; Calabrian arc; Eastern Sicily; Southern Italy

1. Introduction The Calabrian arc and Eastern Sicily are the most seismically active regions of Southern Italy, displaying the effects of an intense Quaternary tectonics mainly represented by a huge regional uplift and by normal faulting consistent with a regional WNW–ESE oriented extension. The regional tectonic uplift started since about 0.6 Ma (Westaway, 1993; Tortorici et al., 1995) and produced the emergence of the entire orogenic belt, including the Lower–Middle Pleistocene syncollisional sedimentary basins of the Tyrrhenian side of the arc (Mesima, Gioia Tauro, Reggio Calabria and Barcellona Basins), and of the south-eastern Sicily foredeep. Tectonic uplift was accompanied by marine terracing along the basin margins and, on land, by deep entrenchment of rivers with the consequent deposition of alluvial and/or transitional coarse grained sediments along the major depressions on top of Lower–Middle Pleistocene pelagic sequences. Normal faulting affects the Tyrrhenian side of ⁎ Corresponding author. E-mail address: [email protected] (L. Tortorici). 0040-1951/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2007.05.008

Calabria and, through the Strait of Messina, the Ionian coast of Sicily forming the Siculo–Calabrian Rift Zone (SCRZ) (Monaco et al., 1997; Monaco and Tortorici, 2000) that develops both offshore and on land with 10 to 50 km-long distinct fault segments (Fig. 1). Relations between the large crustal earthquakes occurring in this region (Postpischl, 1985; Boschi et al., 1995) and tectonic structures have been suggested for the major fault segments of the SCRZ that consequently represent the major seismogenic sources of Southern Italy (Ghisetti, 1992; Valensise and Pantosti, 1992; Westaway, 1993; Tortorici et al., 1995; Monaco and Tortorici, 2000; Jacques et al., 2001; Amoruso et al., 2002; Galli and Bosi, 2002; Tinti et al., 2004). In this paper we try to estimate the Late Quaternary deformation rates of the most active portion of the SCRZ combining the available information with new data to yield new constraints on the significance and role of the SCRZ in the frame of kinematics and seismotectonic picture of Southern Italy. In order to evaaluate the recent activity of the SCRZ and to estimate long-term sliprates and relation with the major seismotectonic parameters, a detailed study of the major fault scarps has been carried out by combining morphological and structural information based on

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Fig. 1. Seismotectonic map of the Siculo–Calabrian Rift Zone (SCRZ). Faults are mainly normal with barbs on downthrown block. Black dots and numbers indicate the major historical and instrumental crustal earthquakes occurred in the last six centuries as reported in the inset (data from Postpischl 1985; Boschi et al., 1995, 1997). Large arrows indicate the regional extension direction (data from Monaco and Tortorici, 2000). Boxes indicate the locations of Figs. 2–5. RIF: Rosolini–Ispica faults; AF: Avola fault; WF: Western Ionian fault; EF: Eastern Ionian fault; ASF: Acireale–S. Alfio faults; PF: Piedimonte fault; TF: Taormina fault; RCF: Reggio Calabria fault; AR: Armo fault; SF: Scilla fault; SEF: S. Eufemia fault; CF: Cittanova fault; SRF: Serre fault; VF: Vibo fault; CVF: Capo Vaticano fault; N-CoF: Nicotera– Coccorino faults.

the analysis of satellite imageries, aerial photographs, topographic maps, field observations and, for the segments extending offshore, by interpreting available seismic profiles. Time constraints for evaluating the fault activity have been obtained by analysing the lateral and vertical distribution of Quaternary stratigraphic markers. In particular new data regard the distribution and the age determination of distinct levels of marine terraces and a detailed analysis of the major fault escarpments. The occurrence of the well dated 0.9–0.6 Ma old

marine sequences uplifted at an elevation up to 1200 m (Aspromonte massif), together with younger flights of marine terraces developed since the Oxygen Isotopic Timescale (OIT) stage 15 (580 ka) are crucial to estimate the Quaternary deformation with the time-resolution of the OIT stages. Particularly, taking into account that around the major active normal fault segments marine terraces are severely deformed according to the flexural cantilever model (King et al., 1988; Kusznir et al., 1991), they represent very useful tools to

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estimate the long-term growth-rate of the active structures. Along the fault segments occurring on-land, marine terraces are significant to date the cumulative fault escarpment for estimating the long-term throw-rate. As regards the coastbounding fault segments marine terraces can indeed be used to estimate the faulting-induced component of footwall uplift. Based on the collected data, we thus discuss the tectonic significance of the SCRZ and its seismotectonic behaviour. 2. Quaternary uplift The Calabrian arc and surrounding regions experienced one of the most intense Quaternary uplift of the whole Mediterranean. Uplift and extension are viewed as a response to stalling of slab retreat and consequent asthenospheric flow into the gap resulting from slab detachment (Wortel and Spakman, 2000; Goes et al., 2004), or as being supported by asthenosphere wedging beneath the decoupled crust (Locardi and Nicolich, 1988; Gvirtzman and Nur, 1999). This process caused the emergence of the entire collisional belt including both the preexisting structural highs, localized at the hanging-wall of the major crustal thrusts, and the intervening syntectonic basins (Monaco et al., 1996). The uplifted basin sediments are represented by neritic to pelagic sequences ranging in age from Early to Middle Pleistocene (Cornette et al., 1987; Catalano and Di Stefano, 1997; Di Stefano and Branca, 2002), thus constraining the onset of the regional uplift at about 600 ka (Westaway, 1993; Monaco et al., 1996). Tectonic uplift has been continuously active during the entire Late Quaternary as recorded by the occurrence in the whole region of uplifted Holocene palaeo-shorelines (Firth et al., 1996; Stewart et al., 1997; De Guidi et al., 2003; Antonioli et al., 2004; Ferranti et al., 2007). Late Quaternary uplift associated with eustatic sea level changes caused the development of prominent flights of marine terraces that represent a peculiar morphological feature of this area (Dumas et al., 1982, 1987; Valensise and Pantosti, 1992; Westaway, 1993; Miyauchi et al., 1994; Bianca et al., 1999; Catalano and De Guidi, 2003; Catalano et al., 2003; Tortorici et al., 2003). Marine terraces originated from vertical displacement above the sea-level of erosional and/or depositional surfaces formed during a relative sea-level stand with their inner edges representing the marine mark of a major highstand of the eustatic curve (Bloom et al., 1974). This implies that marine terrace could be related to the main interglacial OIT stages characterizing the Quaternary (Chappel and Shackleton, 1986; Bassinot et al., 1994; Waelbroeck et al., 2002). Therefore, combining age and elevation of inner edges with the OIT stages of high sea level stands and absolute sea level variations, it is possible to evaluate the upliftrates occurring in a raising region. Considering that the uplift process affected basin sediments as young as 600 ka, marine terracing was effective at least since the OIT stage 15 (580 ka). The vertical distribution of the Late Quaternary marine terraces have also been influenced by deformation exerted around the major active normal fault segments of the SCRZ. As a consequence, the marine terrace distribution records both the regional uplift and the fault related vertical deformation. Therefore, to

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accurately estimate the faulting-induced component of uplift around the major faults of the SCRZ, the regional signal of uplift has to be preventively estimated. Following the fault deformation model proposed by King et al. (1988), the fault related vertical deformation can be considered significant within a 50 km wide belt centred on the fault segment. Thus, uplift estimations carried out sufficiently far from active fault segments approximate the regional signal of uplift. In particular we estimate the regional uplift along the Ionian coast of Calabria, the Tyrrhenian side of Sicily and on the Hyblean plateau. The oldest marine terrace is represented by a several-km wide erosional platform capped by continental deposits. This platform extends continuously on the major mountain ranges (Serre, Aspromonte, Peloritani and Nebrodi) where undercuts relics of mature continental surfaces. At places, it develops directly above the top of the Middle Pleistocene pelagic sequences thus representing the marine mark of the OIT stage 15 (580 ka). Usually the younger marine terraces are represented by six main platforms that could be related to the OIT stages from 13 to 3, as also constrained by several absolute dating carried out in different sites of the entire region (Dumas et al., 1982, 1987; Miyauchi et al., 1994; Balescu et al., 1997; Bordoni and Valensise, 1998; Tortorici et al., 2003). Based on the altitude distribution of the distinct orders of marine terraces coupled with biostratigraphic information together with available absolute dating, the pattern of the regional signal of uplift has been reconstructed. Regional uplift estimations range from 0.2– 0.6 mm/a along the frontal portion of the arc, to values higher than 1.0 mm/a on the axial zone of the chain along the Tyrrhenian coasts (Westaway, 1993; Bordoni and Valensise, 1998; Bianca et al., 1999; Catalano et al., 2003). 3. The Siculo–Calabrian Rift Zone The SCRZ is the major Late Quaternary tectonic feature of the Calabrian Arc and Eastern Sicily. It accomodates an ESE–WNW trending regional extension, as deduced from structural analysis (Tortorici et al., 1995; Monaco et al., 1997; Jacques et al., 2001), seismological data (Cello et al., 1982; Gasparini et al., 1982; Anderson and Jackson, 1987; Frepoli and Amato, 2000; Pondrelli et al., 2002; Jenny et al., 2006) and from VLBI (Ward, 1994) and GPS (D'Agostino and Selvaggi, 2004; Goes et al., 2004) velocity fields. This major normal fault belt runs along the inner side of the Calabrian arc extending through the Straits of Messina along the Ionian coast of Sicily as far as the Hyblean Plateau for a total length of about 370 km (Fig. 1). The distinct normal fault segments exhibit impressive fault scarps which on land define the fronts of the main mountain ranges of the region (Hyblean, Aspromonte and Serre), and offshore bound well developed syntectonic basins (Bianca et al., 1999). Fault segments have lengths ranging from 10 to 50 km and are arranged in three main branches characterized by different orientation. To the south the SCRZ strikes NE forming the Southern Hyblean Branch whereas to the north the fault system swings to a NNW direction constituting the Ionian–Etnean Branch. This latter extends from the Hyblean offshore to the northeastern flank of Mt. Etna from which it swings again to a NE direction forming the Straits of Messina Branch that propagates from the northeastern Sicily to the southern Calabria.

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3.1. Southern Hyblean Branch Along this branch the SCRZ is represented by NE-striking normal fault segments that bound to the southeast the Hyblean Plateau (Fig. 1). The major segment of this branch is the Avola Fault (AF), a 20 km long, east-dipping normal fault that extends from Cassibile to Noto (Fig. 2). The fault displays a very sharp morphology, defined by a steep, linear cumulative scarp which exhibits well developed triangular facets. It is also characterized along strike by heights progressively decreasing towards its northern and southern tips. The uplifted footwall consists of Miocene carbonate rocks directly overlain by remnants of a large old erosional platform (Bianca et al., 1999) that is affected by a large antiform with axial trace perpendicular to the fault plane and hinge zone located around the centre of the fault. The offset of the erosional platform reaches the maximum value of 290 m. On the hanging-wall, the Miocene deposits are unconformably covered by beach calcarenites forming two distinct orders of marine terraces that, showing the inner edges located at elevations of 50 and 25 m, have been attributed to the OIT stage 5 (Bianca et al., 1999). Remnants of an older marine erosional surface related to the OIT stage 7 are in place recognizable at the base of the fault scarp. The hanging-wall is also characterized by the occurrence of large, still active, alluvial fans that, covering the entire flight of marine terraces, developed along the fault escarpment. The drainage network flows almost perpendicular to the fault trace and it is characterized by two deeply entrenched stream generations in the uplifted footwall and of large flat valleys on down-dropped hanging-wall (Fig. 2). On the footwall block, the major stream is represented by the Cassibile River that perches the Hyblean Plateau with deep-sunken meanders. It forms a spectacular canyon (Fig. 2) that, developed for a total length of about 15 km along the hinge zone of the footwall-antiform, is entrenched for about 250 m close to the fault trace. The Cassibile canyon is

characterized by a very narrow drainage basin (only 2–3 km wide) that separates two main drainage patterns flowing along the limbs of the footwall-antiform towards the notheastern and southwestern tips of the Avola Fault. To the South (Fig. 2), the Hyblean Plateau is bordered by two main right-stepping, N 30°E trending and east-dipping normal fault (pitch = 90°) segments, which extend between the villages of Rosolini and Ispica (Rosolini–Ispica fault system of Bianca et al., 1999; RIF). The fault segments extend for a total length of about 20 km and offset a large wave cut platform surface modelled on the Oligo-Miocene carbonates. They are characterised by very sharp, 35 m high linear scarps that near Rosolini show along the base a 0.5 m high, light-coloured scarplet extending for about 4 km (Monaco and Tortorici, 2000). Antecedent streams forming deeply entrenched channels and scarp-related gullies characterize the uplifted blocks, whereas a low-energy relief fluvial landscape developed on the hanging-wall block. These morphological features strongly suggest a very young, mostly Late PleistoceneHolocene, activity for all these fault-segments. 3.2. Ionian–Etnean Branch The Ionian–Etnean Branch of the SCRZ extends with a NNW direction from the offshore of Siracusa to the eastern slope of Mt. Etna (Fig. 1). The major fault segments are represented by the Western and Eastern Ionian faults that develop offshore for lengths of about 50 and 40 km, respectively. Defined by the analyses of a dense grid of seismic reflection profiles (Hirn et al., 1997; Bianca et al., 1999), they are represented by two large eastward convex arc-shaped major faults showing an overall right-stepping en echelon arrangement. They bound a series of eye-shaped half-grabens which constitute sedimentary basins infilled by up to 800 m-thick syn-rift clastic wedges that thicken towards the border faults (Fig. 13 in Bianca et al., 1999). The Western and Eastern Ionian faults dip eastwards at 60°–70° and

Fig. 2. 3D coloured and shaded prospective projection of digital elevation model of the eastern part of the Hyblean Plateau, generated on a geographic grid of 10 × 10 points per km2 with elevation resolution at 25 m. View from N 70°E illuminated from northwest. The picture shows the well defined escarpment of the Avola fault (AF) that runs along the mountain front of the eastern Hyblean Plateau. The footwall is characterized by a well developed old erosional platform and by a drainage network that, flowing almost perpendicular to the fault trace, is made up of deeply entrenched streams (e.g. the Cassibile canyon). To the South the distinct segments of the Rosolini–Ispica fault system (RIF) are clearly visible.

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propagate, at depth, in the laminated lower crust/mantle boundary of the Ionian domain (Cernobori et al., 1996; Hirn et al., 1997). The Eastern Ionian Fault entirely develops within the thinned crust of the Ionian realm whereas the Western segment, between Augusta and Siracusa, partially re-activates the Malta escarpment (Bianca et al., 1999). The effects of the footwall uplift of the Western Ionian Fault are recorded along the eastern coast of the Hyblean plateau where a flight of Middle-Upper Pleistocene marine terraces occurs. Effects of faulting deformation of the Western Ionian Fault are also recognizable on-land, in the area of Catania where a flight of six severely uplifted MiddleUpper Pleistocene marine terraces is exposed (Monaco et al., 2002). In this area, Holocene uplift has been recently detected by analysis of well-logs carried out along the coastal plain (Monaco et al., 2004). In the Etnean area the SCRZ shifts to the west towards the coast with several NNW oriented segments that propagate on land affecting the eastern flank of Etna volcano (Monaco et al., 1997). The most impressive fault segments extend from the coast of Acireale to the S. Alfio village (Acireale-S. Alfio Fault system; ASF in Fig. 1) The distinct segments (Acireale, S. Leonardello and S. Alfio) form a N160°E trending array (Fig. 3), with steeply east-dipping master fault planes characterized by sharp, fairly linear scarps that offset volcanic products ranging in age from about 168 ka to the Present (Monaco et al., 1997), with different cumulative scarp heights along their strike. Oblique slickensides with pitches ranging between 30° and 50°, observed on the Acirale–S. Alfio fault planes, indicate a right-lateral component of slip for the entire NNW–SSE Ionian–Etnean branch of the SCRZ consistent with a roughly ESE (N 100°E) extension direction (Fig. 1). 3.3. Straits of Messina Branch At the north-eastern flank of Mt. Etna the normal fault segments of the SCRZ swing to a NE strike extending from the coastal area of Sicily to the Tyrrhenian side of southern Calabria across the Straits of Messina (Fig. 1).

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In the northeastern slope of Mt. Etna, the fault system is represented by the 15 km-long Piedimonte Fault (PF). This fault exhibits a very sharp cumulative escarpment (Fig. 3) across the 35 ka-old volcanics, and offsets marine terraced sediments that, deposited above the 168 ka old volcanics, may be assigned to the OIT stage 5.5 (Monaco et al., 1997). Northwards, the fault belt is represented by the Taormina Fault (TF in Fi. 1) that extends along the Ionian offshore bounding the Peloritani Mountain range (Catalano and De Guidi, 2003). The Late Quaternary activity of this fault segment is clearly indicated by the occurrence of severely uplifted Upper Pleistocene marine terraces and Holocene paleoshorelines developed on its footwall. Upper Pleistocene marine terraces are represented by five distinct orders that have been assigned (Catalano et al., 2003) to the OIT stages ranging between 5.5 (125 ka) and 3.1 (40 ka). This flight of terraces is characterized by strandlines that, along the strike of the fault segment, depict a large antiform. Along the limbs, the strandlines dip with a convergent array forming two steep ramps that represent the morphological expression of the northern and southern tips of the Taormina Fault thus constraining a fault length of about 40 km. Along the southern edge of the fault segment, Holocene marine notches, uplifted up to 5.5 m and assigned to the last 5 ka (Stewart et al., 1997; Kershaw, 2000; De Guidi et al., 2003), dip towards the southern tip of the Taormina Fault as well as the Late Pleistocene strandlines. In the Straits of Messina region the major fault segments extend along the Calabrian side. The main segment is represented by the 15 km-long NNE-striking Reggio Calabria Fault (RCF) that has controlled the Middle-Late Pleistocene evolution of the Reggio Calabria half graben (Ghisetti, 1981; Barrier, 1987; Tortorici et al., 1995). The fault offsets the 125 ka old sediments and a flight of marine terraces ranging in age from 118 ± 13 ka to 64 ± 8 ka (Balescu et al., 1997), assigned to the OIT stages 5.5–3.3 (Catalano et al., 2003), that occur at different elevations on both the upthrown and downthrown blocks. On the downthrown block continental alluvial deposits representing the remnants of large gently sloping alluvial fans of Wurmian age

Fig. 3. 3D coloured and shaded prospective projection of digital elevation model of the eastern flank of Mt. Etna, generated on a geographic grid of 35 × 35 points per km2 with elevation resolution at 10 m. View from N 70°E illuminated from northwest. The N 160°E-striking distinct east-dipping segments of the Acireale (ACF) S. Leonardello (SLF) and S. Alfio (SAF) faults system defined by sharp and linear scarps are clearly exposed. To the North the cumulative escarpment of the N 30°Estriking Piedimonte fault (PF) is shown.

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(Dumas et al., 1978) unconformably cover the marine sequence and progressively onlap the fault plane thus suggesting faulting activity during that period. The fault plane steeply dips westward and deforms both the crystalline rocks and the Pleistocene sediments. The fault trace runs more or less continuously near the coastline as far as Reggio Calabria from where it seems to continue offshore for about 10 km (Ambrosetti et al., 1987). Morphologically it is defined by a 70–100 m-high escarpment which extends discontinuously at the boundary between the mountain front and the adjacent coastal plain (Fig. 4). Several proximal alluvial fans occur at the base of the fault escarpment that is characterized by one set of triangular facets showing heights ranging from 50 m to 70 m. To the south the west-facing Armo Fault segment (ARF in Fig. 4) extends for a total length of 8 km along a NE–SW direction bounding the western side of the Pleistocene Reggio Calabria basin (Ghisetti, 1992). To the north, the Reggio Calabria Fault overlaps, with a left stepping geometry, the Scilla Fault (SF) that extends from Villa S. Giovanni for about 25 km along the Tyrrhenian offshore bounding to the north the 600 m-high sea-cliff of the Palmi-Bagnara ridge (Fig. 4). The footwall of the Scilla Fault is carved by Late Quaternary marine terraces that are well developed at the tips of the fault segment. At the northern tip (southern border of the Gioia Tauro basin) five marine surfaces are exposed whereas, at the southern ones, on the relay ramp between the Scilla and Reggio Calabria faults, the entire flight of marine terraces are represented by seven orders of surfaces. In this area thermoluminescence (TL) dating (Balescu et al., 1997) provides to assign the lowest marine surface, exposed at an altitude of 48 m, to the OIT stage 3.3 (60 ka). Taking into account this age constraint, the seven orders of terraces could thus be assigned to the OIT stages 5.1 (80 ka), 5.5 (125 ka), 7.5 (240 ka), 9.3 (330 ka), 11.3 (410 ka) and 13 (480 ka). The 480 ka old surface widely extends at the top of the footwall of the Scilla Fault depicting the fault related deformation (Fig. 4). It is tilted southeastward of 7° and along strike it gently dips toward the

northeast changing in elevation from 610 m, near the village of Scilla, to 500 m near to the Palmi Calabro. Southwest of the village of Scilla, along the coastline, Holocene raised fossiliferous beach deposits dated at 2.4–3.9 ka crop out at elevations ranging between 2 and 3.6 m (Antonioli et al., 2004; Ferranti et al., 2008-this issue). To the east the S. Eufemia Fault (Fig. 4) is a northeast dipping, ENE-striking segment that, extending for a length of about 18 km, bounds southward the Gioia Tauro basin. The fault plane affects the Pleistocene sediments and it is marked by about 100 m-wide cataclastic belt characterized in places by slivers of clay-rich fault gouge. Shear planes in the crystalline footwall rocks show oblique slickenlines (pitches of 35°–70°) consistent with a left-lateral component of slip and a N135°E ±5° extension direction (Tortorici et al., 1995). The cumulative escarpment of this fault is characterized by two sets of triangular facets separated by wine-glass valleys and shows a maximum height of 300 m offsetting the 480 ka-old terrace (Tortorici et al., 1995). The Cittanova Fault (CF) extends for a length of about 35 km (Fig. 1) and bounds to the east the Gioia Tauro basin which is filled by a 600 m-thick Pleistocene marine sequence containing at the top pumice rich levels. These horizons may be correlated to similar deposits that, dated at about 600 ka (Cornette et al., 1987), characterize the Quaternary sediments of the Reggio Calabria basin. This age is also consistent to that obtained for the top of the marine sequence infilling the adjacent Mesima basin (see below). The marine sequence is unconformably covered by Middle-Upper Pleistocene alluvial fan conglomerates and sands capped by a wide planation surface (Tortorici et al., 1995). The Pleistocene sediments are severely warped all along the fault plane which is marked by a 50 m wide cataclastic zone including a 1–2 m-thick gouge zone, mostly developed into the footwall crystalline rocks (Tortorici et al., 1995). Mesostructural analysis of the gouge indicates dip-slip movement and N140°E ± 10° extension (Tapponnier et al., 1987; Tortorici et al., 1995). The CF exhibits (Fig. 4) a cumulative scarp that,

Fig. 4. 3D coloured and shaded prospective projection of digital elevation model of the Calabrian side of the Straits of Messina, generated on a geographic grid of 7 × 7 points per km2 with elevation resolution at 20 m. View from N 240°E illuminated from northwest. The distinct fault segments affecting the Calabrian side of the Straits of Messina are clearly defined by well developed rectilinear scarps characterized by the occurrence of triangular facets. Different orders of the largest marine terraces (e.g. 580 and 480 ka-old surfaces) are also visible. ARF: Armo fault; RCF: Reggio Calabria fault; SF: Scilla fault; SEF: S. Eufemia fault; CF: Cittanova fault.

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reaching a maximum height of 700 m, is modelled by three distinct sets of well developed triangular facets (Tortorici et al., 1995). Near S. Cristina d'Aspromonte the youngest triangular facets are separated by narrow V shaped and “wine glass” valleys. On the footwall two further terrace levels are exposed (Ghisetti, 1981; Dumas et al., 1982, 1987; Tortorici et al., 1995). The uppermost surface, ascribed to the OIT stage 15 (580 ka) lies at the top-hill forming the wide Quaternary platform described by Gignoux (1913) and Lembke (1931), which represents a peculiar feature of the Aspromonte mountain range. The lower surface, is carved indeed on the fault escarpment at an elevation of about 700 m, 250 m higher than the fault trace, just above the second set of triangular facets. Northwards the Cittanova Fault forms a left stepping en echelon array with the NNE-striking Galatro and Serre fault segments (Fig. 5). The Galatro Fault (GF) is only 6 km long, with a 150 m-high cumulative escarpment and it probably represents the northernmost segment of the Cittanova Fault with which it may merge at depth (Jacques et al., 2001). The WNW-dipping Serre Fault (SF) is characterized by a 30 km long cumulative escarpment that represents the eastern boundary of the Pleistocene Mesima basin (Fig. 5). This is an half-graben filled with a wedge shaped marine sequence onlapping to the west the Capo Vaticano high. The marine se-

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quence contains nannofossil assemblages indicating an age ranging between 1.3 and 0.6–0.5 Ma and are capped by several orders of terraced alluvial deposits. The Serre Fault exhibits an up to 380 m-high cumulative scarp that is characterized by narrow deep entrenched V-shaped valley separating welldeveloped triangular or trapezoidal facets along the mountain front. The footwall is carved by two orders of terraced surfaces that represent the northern prolongation of the platforms attributed to the OIT stages 15 (580 ka) and 13 (480 ka), respectively. To the west, the fault belt is characterized by a series of normal fault segments that define the structural high of Capo Vaticano peninsula. The peninsula is carved by seven orders of marine terraces, ranging in age from 330 ka to 60 ka that form a NE dipping converging set (Tortorici et al., 2003). The terraces developed at a synthetic relay ramp located between two main NE-striking right-stepping normal fault segments. The northern fault segment (Vibo Fault; VF) extends for a total length of about 25 km from the coast of Vibo village propagating to the north along the foothills of the S. Eufemia plain (Fig. 5). This fault is characterized by a very sharp, mostly undissected fault scarp that reaches a cumulative height up to 280 m. The southern segment extends offshore (Capo Vaticano Fault; CVF in Fig. 1) and bounds to the west the Capo Vaticano high. It offsets the sea-

Fig. 5. 3D coloured and shaded prospective projection of digital elevation model of the Capo Vaticano–Serre area, generated on a geographic grid of 7 × 7 points per km2 with elevation resolution at 20 m. View from N 260°E illuminated from northwest. The picture shows the Serre fault escarpment (SF) that, characterized by the occurrence of well developed triangular facets, extends along the Serre mountain front bounding the Pleistocene Mesima Basin. The very sharp escarpments of the Nicotera (NF) and Coccorino (CoF) fault segments bounding to the South the Capo Vaticano peninsula are shown. Different orders of the largest marine terraces carved on the Serre Mountain range and on to the Capo Vaticano peninsula are also visible (e.g. 580 and 330 ka old surfaces).

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bottom creating a 370 m-high cumulative fault scarp as detected by seismic profiles (Trincardi et al., 1987; Tortorici et al., 2003). To the south-west, the promontory is abruptly truncated by two main ESE-striking, S-dipping normal fault segments (the Coccorino and Nicotera Faults; NF and CoF in Fig. 5) which separate the structural high of Capo Vaticano from the Gioia Tauro Basin. These faults are characterized by ≈ 300–360 mhigh rectilinear cumulative scarps that, truncating the entire flight of marine terraces (Tortorici et al., 2003), extend offshore defining the bathymetry of the southern part of Capo Vaticano (Argnani and Trincardi, 1988). The geometric relations between the NE-striking fault segments of the Straits of Messina Branch and the Nicotera and Coccorino Faults, suggest that these latter may represent a transfer fault zone linking the normal faults of Capo Vaticano–Serre domain with the Gioia Tauro-Straits of Messina domain of the SCRZ (Tortorici et al., 2003). 4. Slip-rates on SCRZ fault segments The distinct fault segments of the SCRZ have very impressive effects on the Late Pleistocene to Holocene morphology controlling the evolution of large portions of coastal areas and creating onshore well developed cumulative scarps. These effects represent useful tools to evaluate the Late Quaternary deformation rates along the entire fault belt. The fault deformation can be directly obtained by analysing the fault scarps exposed on-land or investigated offshore by seismic profiles. Deformation rates for fault segments extending offshore can be also inferred analysing the footwall uplift occurring along the coastal areas. Cumulative fault scarps may be considered as the result of repeated coseismic displacements including footwall uplift and hanging-wall subsidence. On land the fault scarps are usually completely exposed thus reflecting the entire displacement whereas offshore they are mostly concealed by syntectonic sediments deposited on the subsiding hanging-wall. This implies that for

fault segments extending offshore it is necessary to evaluate the thickness of the syntectonic sediments to estimate the total amount of the vertical displacement. This information is also useful to define, the footwall uplift/hanging-wall downdrop (u/d) ratio that, depending on the elastic response of the seismogenic layer (upper crust), could be considered almost uniform for areas with similar crustal layering. The u/d ratio has thus application in deciphering the total vertical displacement occurring along coast-bounding fault segments starting from the values of the footwall uplift. Along the coastal areas located on the footwall of fault segments extending offshore, these values represent however only a part of the total uplift which also includes the regional and the postseismic components of the vertical motion. Based on the detailed analysis of seismic reflection profiles carried out along the Western and Eastern Ionian faults, Bianca et al. (1999) propose a value of 1/1.6 for the u/d ratio. As regards the partitioning of the vertical motion along the SCRZ, the regional component ranges from 1.1 mm/a in the Tyrrhenian coasts to 0.26 mm/a in the Hyblean foreland region. Finally the post-seismic component of the footwall uplift may range from 25% to 30% of the fault-induced vertical deformation of the footwall as estimated by the short-term behaviour of the Taormina Fault (De Guidi et al., 2003). Following this methodological approach slip-rates along the major fault segments of the distinct branches of the SCRZ have been estimated as summarized in Table 1. To the south, in the Southern Hyblean Branch, slip rates have been evaluated on the Avola Fault that shows a 290 m-high cumulative scarp bounding a mountain range characterized by a deeply entrenched drainage system. On the footwall the entrenchment of rivers modified the primary features of the antecedent drainage pattern represented by the hanging consequent streams and by the inherited meandering courses. This suggests that a mature fluvial landscape developed near the base-level for a long time before the onset of the Avola fault activity. This implies that the growth of the Avola Fault caused the entrenching

Table 1 Principal seismotectonic parameters obtained for the major active fault segments of the SCRZ Fault segment

L (km)

Tmax (m)

Time (ka)

Smax (mm/a)

Markers

M

Mmax

Earthquakes M

Date

Avola (AF) W-fault (WF) Acireale (AcF) S. Leonardello (SLF) S. Alfio (SAF) Piedimonte (PF) Taormina (TF) Reggio (RCF) Scilla (SF) S. Eufemia (SEF) Cittanova (CF) Serre (SF) C. Vaticano (CVF)

20 50 10 12 7 15 40 25 25 18 35 30 30

290

240–200 330 168–100 14 60–80 35 b10 60 b10 125 580 580 330

1.3 ± 0.1 3.1 1.5 ± 0.4 1.8 1.7 ± 0.3 1.7 1.8 ± 0.5 1.4 ± 0.3 1.1-1.3 0.7 1.2 0.7 2.1 ± 0.1

Morphological features Seismic data, footwall terracing, u/d ratio Lava flow offset Lava flow offset Lava flow offset Lava flow offset Footwall terracing, u/d ratio Morphological features Footwall terracing Morphological features Morphological features Morphological features Seismic data, footwall terracing, u/d ratio

6.6 7.0 6.4 6.4 6.2 6.5 6.9 6.7 6.7 6.6 6.9 6.8 6.8

6.9 7.3 6.6 6.7 6.4 6.8 7.2 7.0 7.0 6.9 7.1 7.1 7.1

4.8 7.5 5.6 5.2 5.8 5.6 ? 7.1 6.1 5.7 7.1 6.7 7.0

09-01-1693 11-01-1693 20-02-1818 08-03-1950 15-10-1911 19-07-1865 853 AD (?) 28-12-1908 06-02-1783 16-11-1894 05-02-1783 07-02-1783 08-09-1905

190 25 120 60 70–100 70–80 700 380

L: length of the major investigated fault scarp; Tmax: maximum throw measured along the fault scarp; Time: age constraints; Smax: maximum vertical slip-rate; M: most likely magnitude (best-fit curve; uncertainty ±0.1) based on L; Mmax: maximum possible magnitude (worst case scenario; uncertainty ±0.1) based on L; Earthquakes: magnitude and date of the major seismic events occurring along the SCRZ (data are from Postpischl 1985; Boschi et al., 1995, 1997). The values of M and Mmax, are obtained from the empirical relationships of Pavlides and Caputo (2004).

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of the drainage pattern on the footwall and, on the hanging-wall, the deposition of the alluvial fans that developed above the OIT stage 7 old marine terrace. This suggests that the onset of the Avola Fault could have occurred at least since the 200–240 ka, thus implying that the 290 m-high fault escarpment developed at a throw-rate ranging from 1.2 to 1.4 mm/a. To the north, along the Ionian–Etnean Branch, slip-rates have been evaluated along the Western and Eastern faults, located offshore and along the distinct fault segments affecting on-land the eastern flank of Mt. Etna. Detailed analysis of seismic reflection profiles carried out on the Ionian offshore, revealed long term throw-rates of 2.6 mm/a and 3.1 mm/a on the Eastern Ionian and Western Ionian faults, respectively, for the last 330 ka (Bianca et al., 1999). Throw-rates on the distinct onland fault segments affecting the eastern flank of Mt. Etna have been evaluated along the fault escarpments affecting very recent volcanic products (Monaco et al., 1997). The S. Alfio Fault cuts 80 to 60 ka old basalts with a total vertical displacement of 120 m with a long term throw-rate of 1.5–2.0 mm/a. The S. Alfio Fault also offsets by 5 m prehistoric lava flows with age ranging between 5 ka and 2.4 ka, and by 1.5 m the 1284 AD lava flow with a short-term slip-rate of 2.1 mm/a. Similar throwrates have been estimated on the S. Leonardello Fault, that offsets by ~ 1.5 m, the 9th century lava flow, and on the Acireale Fault segment that with a scarp reaching 190 m cuts a volcanic sequence mainly made of 170 to 100 ka-old basalts. Along the Straits of Messina branch, throw-rates have been evaluated for both offshore and on-land major fault segments. The Piedimonte Fault cumulated a 60 m high scarp in the last 35 ka with a throw-rate of 1.7 mm/a. This fault also displaces for about 150 m the 125 ka old marine terrace thus constraining a long-term throw-rate of about 1.2 mm/a. Similar values of throw-rates have been estimated also for the Taormina Fault segment by analysing the footwall uplift. On the central portion of the Taormina Fault strandlines related to 125 to 40 ka-old marine terraces carved on the footwall have been uplifted at elevations ranging from 210 m to 19 m, suggesting a Late Pleistocene uplift-rate of about 1.6 mm/a. Assuming for this region a value of 0.8-1.0 mm/a for the regional signal of uplift, a total fault-induced uplift-rate of 0.6–0.8 mm/a can be estimated. Moreover, considering that the post-seismic component represents the 0.25–0.30 of the total fault induced uplift (De Guidi et al., 2003), values of 0.4–0.6 mm/a can be evaluated for the time-averaged coseismic component of the uplift-rates. Finally, u/d ratio of 1/1.6 implies that the long-term throw-rate along the Taormina Fault can be estimated at least at 1.3 ± 0.3 mm/a. The occurrence of 5 ka old marine notches (Stewart et al., 1997; Kershaw, 2000) elevated up to 5.5 m (De Guidi et al., 2003) on the southern portion of the footwall of the Taormina Fault constrains a Holocene uplift-rate of 1.7–2.0 mm/a. These values corrected for the regional and post-seismic uplift and for the u/d ratio implies a short-term throw-rate of 1.8 ± 0.5 mm/a. To the north, the throw-rate has been evaluated along the onshore portion of the Reggio Calabria Fault. The 70–100 m high cumulative scarp of this fault developed in the last 60 ka as shown by the occurrence on its top of the marine terrace assigned to the OIT stage 3.3 thus implying a long term throwrate of 1.4 ± 0.3 mm/a. Moreover, the 50–70 m high triangular

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facets characterizing the fault escarpment represent the result of interactions between the vertical displacement occurring on the fault segment and rates of the erosional processes induced by the climatic cycle started at OIT stage 3 (40 ka). This constrains a time-averaged throw-rate (1.2–1.7 mm/a) which is consistent with that obtained by analysing the cumulative scarp. Along the Scilla Fault the distribution of the marine terraces from the tips to the central portion of the fault segment suggests that the 600 m high escarpment developed in the last 480 ka with a time-averaged rate of footwall uplift of 1.2 mm/a. The occurrence of 2.4–3.9 ka old marine benches elevated up to 3.6 m on the southern portion of the footwall of the Scilla Fault constrains a Holocene throw-rate of about 1.1–1.3 mm/a (Ferranti et al., 2008-this issue). The S. Eufemia Fault cumulated its 300 m high scarp at least since 480 ka. The lowest portion of the escarpment is characterized by the occurrence of 70–80 m high triangular facets whose development could be ascribed to fault-displacement occurred during to the last climatic cycle (since 125 ka to present). This implies that a throw-rate of about 0.7 mm/a could be estimated for the S. Eufemia Fault (Tortorici et al., 1995). The development of the Cittanova Fault scarp was accompanied by terracing on the footwall and by deposition of alluvial fans on the hanging-wall. Continental deposits developed above the marine sequence whose top-levels have been dated at about 600 ka; in addition the older surface resting on the footwall has been assigned to the OIT stage 15 (580 ka). This implies that the 700 m high cumulative fault escarpment developed at least since 580 ka, with a long-term throw-rate of about 1.2 mm/a. Moreover, considering that the Cittanova Fault scarp exhibits three orders of triangular facets with heights of about 400 m, 200–250 m and 80–90 m (Tortorici et al., 1995) and assuming that these orders of facets developed during the last three climatic cycles, throw-rates ranging between 0.7 (Tortorici et al., 1995; Jacques et al., 2001) and 1.2 mm/a are obtained. Along the Serre Fault, the 580 ka old terrace occurring on the footwall pre-dates the growth of the 380 m-high fault escarpment, thus implying a minimum throw-rate of about 0.6– 0.7 mm/a, as also stated by Monaco and Tortorici (2000). The Capo Vaticano Fault segment produced the severe uplift of the entire flight of marine terraces exposed in the Capo Vaticano high (Tortorici et al., 2003), displacing the 330 ka old terrace at a maximum elevation of 710 m in the south-western sector of the peninsula. This implies that the peninsula, located at the footwall of the coast-bounding Capo Vaticano Fault, suffered a long-term maximum uplift-rate of 2.1 ± 0.1 mm/a including both the regional (1 mm/a) and the faulting induced components. As well as for the Taormina Fault segment an approximate vertical slip can be estimated. Considering the corrections due to the regional signal (1.0 mm/a), to the u/d ratio (1/1.6) and to the post-seismic component of footwall uplift (0.25–0.30), a value of about 2.0 mm/a is obtained. Our estimations point out that throw-rates along the distinct fault segments of the SCRZ range from 0.7 to 3.1 mm/a with the highest values (N 2 mm/a) characterizing the Western and the Eastern faults segments of the Ionian–Etnean branch.

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5. Seismicity

5.2. The 1783 southern Calabria earthquake sequence

The SCRZ is characterized, as a whole, by an intense seismicity represented by instrumental and historical crustal earthquakes with maximum magnitudes up to 7.5 and MCS intensities up to XI (Postpischl, 1985; Boschi et al., 1995, 1997). This high level seismic belt is interrupted in the Mt. Etna region where a very shallow seismicity with events with Mmax ≅ 6.1 and MCS intensities up to X are recorded (Azzaro and Barbano, 2000). The Siculo–Calabrian seismic belt includes the largest earthquakes which have occurred in southern Italy in the last six centuries as the 1693 earthquakes, the 1783 earthquake sequence, the Monteleone earthquake of 1905 and the Messina earthquake of 1908. Relationships between large earthquakes and tectonic structures of the SCRZ have been suggested for the 1693 earthquakes, that have been related to the Avola and the Western Ionian fault segments (Bianca et al., 1999), and for the 1783 sequence, that has been related to ruptures of the fault segments extending in southern Calabria (Jacques et al., 2001; Galli and Bosi, 2002). In this chapter we briefly describe the effects of the major earthquakes occurred along the SCRZ to test the possible relations between seismic events and seismogenic sources.

Between the 5th of February and the 28th of March 1783 the southern Calabria, between Catanzaro and Reggio di Calabria, was ruined by five large earthquakes of MCS intensities between IX and XI (Boschi et al., 1995). The effects of the entire sequence and the relations with ruptures along active faults of southern Calabria have been detailed in Jacques et al. (2001). The first shock of this sequence occurred on February 5 and completely destroyed all the villages located at the western foot of the northern Aspromonte mountain range. The mesoseismal area of this event, characterized by MCS intensity XI, was mainly located on the Gioia Tauro plain at the hanging-wall of the Cittanova Fault. Along this structure, a co-seismic rupture propagated over a length of 18 km (De Dolomieu, 1784; Jacques et al., 2001), from S. Giorgio Morgeto and S. Cristina d'Aspromonte (see Figs. 2 and 4 in Jacques et al., 2001), with an estimated slip of about 3 m (Jacques et al., 2001). The shock produced spectacular morphological effects represented by diffuse landslides that dammed valleys creating many lakes (Hamilton, 1783; Vivenzio, 1783; De Dolomieu, 1784; Baratta, 1901; Cotecchia et al., 1969). The second shock occurred on February 6 and affected the coastal area between Scilla and Palmi with MCS intensity IX-X (Boschi et al., 1995). It was accompanied by the occurrence of large rockslides from the sea-cliff west of Scilla and generated a tsunami that affected the Calabrian coast from Bagnara to Villa S. Giovanni and the Sicilian side of the Straits of Messina from Punta Faro to Messina (Baratta, 1901; Boschi et al., 1995; Tinti et al., 2004), with waves reaching heights of 6–8 m. This strongly suggests that the centre of this second shock was probably located offshore not far from Scilla (Jacques et al., 2001; Ferranti et al., 2008-this issue). The third shock of February 7 ruined all the villages located at the western foot of the Serre mountains. Its mesoseismal area was characterized by a MCS intensity X-XI and was located along the Mesima valley at the hanging-wall of the Serre Fault. Similarly, on March 1, the fourth shock occurred on the northern edge of the Mesima valley about 20 km north of the February 7 epicentre, with a MCS intensity IX-X (Baratta, 1901; Boschi et al., 1995). The sequence ended with the March 28 event that occurred on the Ionian side of the Catanzaro trough affecting a small area with a MCS intensity XI (Boschi et al., 1995). The shocks of the 1783 earthquake sequence have been related to ruptures on the west dipping normal fault segments that affect the southern Calabria (Tapponnier et al., 1987; Monaco and Tortorici, 2000; Jacques et al., 2001; Galli and Bosi, 2002). In a more detail, the first shock has been related to slip on the Cittanova Fault, the second on the offshore Scilla Fault and the third and fourth on the Serre Fault, whereas for the last event the relations with morphogenic faults are still unclear.

5.1. The 1693 south-eastern Sicily earthquakes The 1693 earthquakes consist of two events characterized by MCS intensities of VIII-IX and XI that occurred between the 9th and 11th of January 1693 devastating south-eastern Sicily. The main shock has been described by several authors as the largest earthquake ever recorded in the central Mediterranean (Baratta, 1901; Postpischl, 1985; Boschi et al., 1995; Bianca et al., 1999). The first shock, occurred at 9 pm (GMT) of 9th January, caused severe damages along a narrow belt extending entirely on land along the eastern border of the Hyblean Plateau from Lentini to Noto (Fig. 20a in Bianca et al., 1999). This shock has been related by Bianca et al. (1999) to ruptures occurred along the Avola Fault segment. The second shock occurred about at 1.30 pm (GMT) of 11th January and was catastrophic, devastating the entire southeastern part of Sicily and killing about 54,000 people (Boccone, 1697; Baratta, 1901). Towns and villages located close to the south-eastern coast of Sicily (see Fig. 20b in Bianca et al., 1999), were completely destroyed suffering damages ascribed to an MCS intensity greater than X (Boschi et al., 1995). This shock had impressive effects on the morphology (Fig. 20c in Bianca et al., 1999) with the occurrence of large landslides, several linear fractures and cracks and liquefaction features. The main shock also generated a large tsunami recorded along the whole coast of eastern Sicily, between Messina and Siracusa, and on the island of Malta. The tsunami was characterized by waves up to 12 m-high and flooding onto the shore up to 1.5 km (Baratta, 1901; Bianca et al., 1999; Tinti et al., 2004). The epicentre of this shock has been located along the western fault, offshore the Ionian coast (WF in Fig. 1) not far from the coastline, between Catania and Siracusa (Bianca et al., 1999).

5.3. The 1905 Monteleone earthquake On September 8th, 1905 a large earthquake with M ≅ 7.0 and MCS intensity X-XI occurred offshore the Capo Vaticano

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peninsula (Gasparini et al., 1982; Boschi et al., 1995). This event extensively ruined several villages located in the northern part of the Capo Vaticano peninsula within an area forming a lobe facing to the sea that suffered a MCS intensity greater than IX (Boschi et al., 1995). Large landslides accompanied by several cracks and fractures and liquefaction features occurred in several places within the mesoseismal area. This event also generated a tsunami (Tinti et al., 2004) that inundated the whole northern coast of the peninsula from Vibo to Tropea with an estimated height of waves of about 2.5 m (Piatanesi and Tinti, 2002). The above mentioned macroseismic picture indicates that this event had an epicentre located offshore the northern coast of Capo Vaticano not far from the coastline. This suggests that a relation with slips occurring along the Vibo and Capo Vaticano normal fault segments could be inferred.

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5.4. The 1908 Straits of Messina earthquake This earthquake, the most impressive event of the last century in Southern Italy, occurred with an MCS intensity XI and M = 7.1 (Postpischl, 1985; Boschi et al., 1997) on December 28 striking the entire Straits of Messina area. The area devastated by the main shock was mostly located on the Calabrian side of the Straits extending in the Sicilian coast along a narrow belt including the town of Messina (Fig. 6). In Calabria the mesoseismal area forms two wide NE oriented lobes extending at the hangingwalls of the normal fault segments affecting the area (Armo, S. Eufemia and Reggio Calabria fault segments). Towns and villages located within this area (Reggio di Calabria, S. Eufemia d'Aspromonte, Melia, Mosorrofa, Nasiti, Piale, Villa S. Giovanni, Archi, S. Roberto, Calanna, Lazzaro, Nocella) were completely

Fig. 6. Cartoon showing the mesoseismal areas (MCS scale) and damage distribution of the 1908 Messina earthquake (data from Baratta, 1910; Boschi et al., 1995) related to the fault pattern of the Straits of Messina region. (ARF: Armo fault; RCF: Reggio Calabria fault; SF; Scilla fault; SEF: S. Eufemia fault; CF: Cittanova fault). Focal mechanism is from Cello et al. (1982). Numbers refer to the maximum height (in metres) reached by the tsunami waves (data from Baratta, 1910).

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destroyed suffering damage ascribed to an MCS intensity ≥X (Boschi et al., 1995). In this area, the percentage of ruined buildings was higher than 90% as reported from the chronicle of Baratta (1910). Many other villages (Motta S. Giovanni, Cardeto, Cataforio, S. Stefano d'Aspromonte, Laganadi, and Bagnara), located within a narrow belt (3–4 km wide) surrounding the mesoseismal area, were extensively damaged suffering a percentage of ruined buildings ranging between 45% and 90% (Baratta, 1910) indicating an MCS intensity of IX (Boschi et al., 1995). The main shock caused landslides occurred in several localities such as Reggio di Calabria, Archi, Gallina and Campo Calabro and diffused rockslides along the sea-cliff from Scilla to Bagnara. Together with the occurrence of sand fountains related to liquefaction reported in the Reggio di Calabria area, one of the most impressive coseismic effect was the permanent subsidence, estimated at about 0.70-1.00 m, of the entire coastline from Lazzaro to Bagnara (Baratta, 1910). In Sicily the mesoseismal area is confined near the coast along a few km wide (1–4 km) belt where the town of Messina and surrounding villages (Contessa, Camaro, Pace, Faro, Torre Faro) were completely ruined by shacking and subsequent tsunami. Villages (S. Lucia, Cumia, Bordonaro, Ritiro, Curcuraci, Massa S. Giovanni) with damages ascribed to an MCS intensity of IX (Boschi et al., 1995) define a narrow belt that envelops to the west the mesoseismal zone (Fig. 6). Sand fountains spurted water from linear fractures and cracks developed on the coastal plain from Messina to Ganzirri (Baratta, 1910). Several fractures affected the entire quay of the harbour of Messina depicting an overall arc shaped geometry. These fractures that have also occurred during the main shock of the 1783 earthquake sequence, may represent the surface evidence of the re-activation of the main scarp at the crown of a large submarine landslide. This event also generated a large tsunami (Tinti et al., 2004) that devastating both sides of the Straits of Messina (Fig. 6) was recorded along the entire Ionian coast of eastern Sicily (Monaco et al., 2006) and part of the northern (Tyrrhenian) and southern (Sicily Channel) coasts of the island. The tsunami was characterized by the occurrence of at least three distinct waves which inundated the town of Messina with a maximum height of 2.90 m and the town of Reggio Calabria with heights of 6–7 m. The maximum amplitude of the tsunami wave was recorded along the Ionian coast of Sicily from Furci to Galati Marina with values estimated from 8 to 9.2 m (Baratta, 1910). In southern Calabria the maximum height reached by the wave was 10 m at Lazzaro (Baratta, 1910). The above mentioned observations produce a clear macroseismic picture that strongly suggests as this event could be related to ruptures occurred along the NE trending, west-facing Armo, S. Eufemia and Reggio Calabria fault segments including the offshore propagation of the Reggio Calabria Fault. This interpretation is supported by the analysis of the focal mechanism that shows a slip occurring along a NNE trending, west-facing nodal plane (Riuscetti and Shick, 1975; Shick, 1977) that is consistent with both the macroseismic picture and the regional structural data (Ghisetti, 1984; Montenat et al., 1991; Tortorici et al., 1995). Conversely, based on inversion of

levelling data, slip along a low angle, N–S trending and east– dipping auxiliary nodal plane, merging at the surface on the Sicilian coastline, has been proposed (Capuano et al., 1988; Boschi et al., 1989; De Natale and Pingue, 1991; Valensise and Pantosti, 1992; Amoruso et al., 2002). 6. Expected magnitudes and extension-rates The geological and morphological observations on the SCRZ combined with seismological information, emphasise that the crustal seismicity of this region of southern Italy is related to Late Quaternary normal faulting. These relations are evidenced by the consistency between fault parameters of the major segments (length, throw, slip-rate), the maximum expected magnitude and the historical seismicity (Table 1). To estimate the maximum expected magnitude, several empirical relationships between surface rupture length and magnitude have been proposed by different authors (e.g. Wells and Coppersmith, 1994; Papazachos and Papazachou, 1997; Ambraseys and Jackson, 1998; Pavlides and Caputo, 2004). Here we adopted the relations proposed by Pavlides and Caputo (2004) for the Aegean normal faults as they refer to a geodynamic and crustal frame similar to that characterizing the investigated region. Assuming that along each fault segment the measured morphological throw is the result of repeated coseismic surface displacements occurred during Late Quaternary major seismic events along the entire fault length, both the most likely magnitude (M) and the maximum possible magnitude (Mmax) have been calculated using the Eqs. (1) and (5) proposed by Pavlides and Caputo (2004). The calculated values for all studied fault segments range from 6.2 to 7.0 and from 6.4 to 7.3 for M and Mmax, respectively. The overall range of magnitudes (M = 6.2– 7.3) is, in general, in good agreement with the values reported for the historical and instrumental crustal events except for the fault segments affecting the eastern flank of Mt. Etna. The fault segments (Acireale, S. Leonardello, S. Alfio and Piedimonte segments) of this portion of the SCRZ are associated with shallow historical and instrumental earthquakes characterized by magnitudes (M = 5.1–6.1) sensibly lower than the estimated values (M = 6.2–6.8). This behaviour can be related to the local thinning of the seismogenic layer due to the thermal anomaly connected with the occurrence of the Etnean magmatism. Except for the Mt. Etna district, the regional seismicity related to the activity of the major fault segments of the SCRZ is thus characterized by M ranging from 5.7 to 7.5 which are deeply consistent with the estimated values (M = 6.6–7.3). The measured maximum offsets of different temporal markers indicate that the active normal faults of the SCRZ have been characterized by throw-rates ranging from 0.7 to 3.1 mm/a (Table 1). Assuming that within the seismogenic layer the normal fault segments are characterized by a mean dip angle of 45°, extension-rates have been also estimated for the three major branches of the SCRZ. This implies that the vertical slip estimated for each fault segment can be entirely converted at depth into an equivalent amount of crustal lengthening for all the fault segments characterized by pure dip-slip motion. Values obtained on oblique normal faults have been corrected taking into account the angle

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(α) between the fault-dip and the extension directions to estimate deformation rates along the regional extension direction. In the Southern Hyblean Branch, the extension is entirely accommodated by the Avola Fault (α = 30°) with values of 1.5 ± 0.1 mm/a (transect a in Fig. 7). Along the Ionian–Etnean Branch, taking into account the fault arrangement and the oblique motion on the fault segments, the entire extension can be estimated on the Western Fault (α = 25 °) with values of 3.4 mm/a (transect b in Fig. 7). In the Straits of Messina Branch, the WNW–ESE extension is accommodated and partitioned along a set of NNE–SSW trending fault segments. The extension-rate has been estimated along two transects including the central portions of the Scilla and S. Eufemia faults and the southernmost sector of the Cittanova Fault segment to the south (transect c in Fig. 7), and the central portions of the Capo Vaticano and Serre faults to the north (transect d in Fig. 7). Considering that the SF, SEF and CF are characterize by α = 35°–40°, the first transect cumulates a total extension-rate of 3.0 mm/a whereas, taking into account that

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the CVF and SRF have angles α = 35° and 10° respectively, the second transect shows values of 3.3 mm/a. As a whole our results evidence that the Ionian–Etnean and the Straits of Messina branches of the SCRZ accommodate an almost uniform extension-rate of about 3.0 mm/a being in good agreement with the geodetic data available for the rift zone that show a presentday extension-rate of 3.6 ± 0.6 mm/a along a N 115°E direction (D'Agostino and Selvaggi, 2004). The extension-rates estimated for the Southern Hyblean Branch are indeed significantly lower than the values obtained for the other branches of the SCRZ and the measured geodetic deformation rates. To justify this anomaly we suggest three possible explanations not necessarily alternative to each other: i) the occurrence of possible other important fault segments located offshore that, not considered here, could contribute to accommodate a consistent amount of regional extension; ii) a consistent amount of crustal extension occur as a distributed aseismic deformation or by a minor and diffuse seismicity; iii) the Southern Hyblean Branch represents the southern

Fig. 7. Cartoon showing the active deformation pattern of the SCRZ. A–D shaded areas refer to possible seismotectonic zoning of SCRZ (see text for discussion). Large arrows indicate the regional extension direction as derived from structural data. Thin black arrows refer to the motion of the Sicilian (Noto) and Calabrian (TGRC) crustal blocks in the Europe reference frame. The inset shows the velocity diagram indicating how the regional extension direction responsible for the opening of the SCRZ is the result of the relative motion between the Sicilian and Calabrian crustal blocks (D'Agostino and Selvaggi, 2004). Transects a–d indicate the sections along which extension-rates of the SCRZ have been estimated.

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tip of the SCRZ where the extension decreases to zero. These data suggest that the southern Calabrian Arc and eastern Sicily are dominated by an incipient rifting related to a WNW–ESE regional extension. This process, that develops in the large scale framework of the Africa–Europe collision, is related to the different relative motions occurring between the Sicilian and the Calabrian shoulders in the Europe reference frame (Fig. 7). WNW–ESE extension may be in fact the result of the different directions and rates of motion of the Sicilian and the Calabrian crustal blocks as shown by the velocity diagram combining the NNW oriented vector of Sicily with the NNE trending vector of Southern Calabria (Hollenstein et al., 2003; D'Agostino and Selvaggi, 2004). 7. Conclusions The main results of this study therefore suggest that in this portion of southern Italy rift processes are entirely accommodated by ruptures occurring along the distinct normal fault segments of the SCRZ being responsible for the dominant seismicity of this region (Jenny et al., 2006). Our data indicate moreover that the magnitudes of the historical and instrumental events are consistent with the estimated values obtained with the empirical relations between fault length and magnitude. The geometry and kinematics of fault segments and the related different crustal features of the SCRZ control the different seismic behaviours of adjacent portions of the active fault belt. Low to moderate earthquakes with M ranging from 5.1 to 6.1 are associated with the 7 to 15 km-long fault segments affecting the softened and thinned Etnean crust (A in Fig. 7). Moderate to strong earthquakes (6.6 ≤ M ≤ 6.9) would be peculiar of the Southern Hyblean branch with 20 km-long fault segments (B in Fig. 7). Strong earthquakes (6.7 ≤ M ≤ 7.1) are typical in the Straits of Messina branch characterized by the occurrence of 20 to 35 km-long fault segments trending almost perpendicular to the direction of the extension (C in Fig. 7). The strongest earthquakes with M ≥ 7.2 characterize the Ionian 40 to 50 km-long fault segments that accommodate the regional extension with a huge lateral component of motion (D in Fig. 7). Finally it is note to worth that except for the southernmost portion of the Straits of Messina branch (e.g. the Taormina Fault), during the last six centuries all the fault segments of the SCRZ have been ruptured causing the strong seismicity of the region. References Ambraseys, N.N., Jackson, J.A., 1998. Faulting associated with historical and recent earthquakes in the Eastern Mediterranean region. Geophys. J. Int. 133, 390–406. Ambrosetti, W., Bosi, C., Carraro, F., Ciaranfi, N., Panizza, M., Papani, G., Vezzani, L., Zanferrari, A., 1987. Neotectonic map of Italy. Scale 1:500.000. C.N.R., Rome. Amoruso, A., Crescentini, L., Scarpa, R., 2002. Source parameters of the 1908 Messina Straits, Italy, earthquake from geodetic and seismic data. J. Geophys. Res. 107. doi:10.1029/2001JB000434. Anderson, H., Jackson, J., 1987. The deep seismicity of the Tyrrhenian Sea. Geophys. J. R. Astron. Soc. 91, 613–637. Antonioli, F., Dai Pra, G., Segre, A.G., Sylos-Labini, S., 2004. New data on Late Holocene uplift-rates in the Messina Strait area, Italy. Quat. Nova 8, 45–67.

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