Regional studies on coastal tectonics in Italy
Existing studies of vertical displacements at the Italian coasts have used markers of different age, but two relatively well dated shorelines stands as the prominent benchmarks, namely the Last Interglacial (LIg) and the Holocene strandlines.
The LIg shoreline coincides with the Marine Isotope Sub-stage (MIS) 5.5, which occurred between 132 and 116 kyr (Shackleton et al., 2003), and is thus representative of the intermediate-scale displacements. Along the coasts of the Italian peninsula and islands, the recognized altitude variability of the marker was attributed to tectonic processes, which resulted in differential displacements relative to the predicted eustatic position. Studies dating back to several decades have detailed this occurrence at numerous sites (see references quoted in Ferranti et al., 2006). In the final decade of the last century, pioneering review studies [Cosentino and Gliozzi, (1988) and Bordoni and Valensise (1998), based on the LIg marker; Westaway (1993) and Miyauchi et al. (1994), using the LIg and Middle Pleistocene shorelines] outlined the tectonic displacements occurring at a regional scale in central-southern Italy, and particularly in the Calabrian arc (Fig. 1) where displacement rates are higher. The pattern of rapid uplift was attributed to isostatic or dynamic processes occurring in the lithospheric slab underlying this region (Fig. 1; Cosentino and Gliozzi, 1988; Westaway, 1993). Bordoni and Valensise (1998) in their review of the LIg displacement outlined the interplay between regional and local tectonics to explain the large variability in amplitude and wavelength of the elevation pattern in different parts of southern and central Italy.
Ferranti et al. (2006) provided an updated review of the LIg shoreline position to detect the vertical component of tectonic displacement along the whole coastline of Italy in the last 130 kyr. They used the shoreline displacement drawn from published and in few occurrences from new work, as a means to provide accurate displacement rates and verify existing tectonic models. Using a compilation of 246 sites, Ferranti et al. (2006) observed a significant alongshore difference in site elevation between +175 and –125 m respect to the present sea level, which they attributed to the combination of regional and local processes, including faulting and volcanic deformation. They found that whereas most of Sardinia and the northern Tyrrhenian Sea coasts are tectonically quiescent, the central Tyrrhenian Sea coasts display stable promontories, subsiding plains, and localized centres of weak uplift. Subsidence of the plains was related to extensional faulting locally enhanced by volcano-tectonic collapse, and weak uplift arises from magmatic unrest. Rapid uplift of southern Calabria, northeast Sicily and the Ionian sea coasts was viewed as a response to deep crustal delamination beneath the Calabria forearc terrane. The central Adriatic Sea was found to show weak thrust-related uplift, but foreland flexure in northern Adriatic resulted in locally intense regional subsidence. The rapidly uplifting regions were spatially correlated with the sectors of higher seismic release and surface horizontal motion documented by geodetic velocities, underlining the four-dimensional nature of deformation.
Other studies in the intervening time have detailed the position of the LIg shoreline at few more locales. New LIg data, mostly from the Venetian plain, were provided by Antonioli et al. (2009) in their recent analysis of Holocene relative sea-level changes along the Italian and Istrian coastlines. In the south, along the Ionian Sea coast of northern Calabria and Lucania, Westaway and Bridgland (2007), Santoro et al. (2009), Ferranti et al. (2009) and Caputo et al (2010) have provided new observations on Middle Pleistocene and LIg shoreline position. The works of Santoro et al. (2009) and Ferranti et al. (2009) have shown that a regional and a local component are embedded in the deformation profile of Middle-Late Pleistocene marine terraces in north-eastern Calabria. The magnitude of the regional component is almost four times greater than the local component, the latter being attributed to growing folds within a transpressive displacement field. Further to the north, different interpretation of the displacement pattern were published by Westaway and Bridgland (2007) and Caputo et al (2010) in eastern Lucania. Whereas the first authors highlighted the thermal response to sediment load in promoting crustal uplift through lower crustal flow directed beneath regions of prevailing erosion, the latter have stressed the contribution of deep crustal and lithospheric contraction versus shallow-crustal folds. Along the Tyrrhenian sea coast of Calabria, Cucci and Tertulliani (2006) have provided an updated review of Pleistocene coastal terraces at Capo Vaticano (following previous work by Miyauchi et al., 1994 and by Tortorici et al., 2003) and identified the contribution of a local extensional fault as being lower than regional uplift. New studies on coastal tectonics in Italy have recently appeared on a Special Issue of Quaternary International (Antonioli et al., 2011).
Short-term markers of deformation are represented by Holocene shorelines and geoarcheological markers of sea-level changes. Pioneering works of synthesis on Holocene displacements in the Calabrian arc were carried by Pirazzoli et al. (1997), Lambeck et al. (2004), and Antonioli et al. (2006). The latter authors found average uplift rates during the Holocene were consistently higher (64 to 124%) than longer-term rates, but the location of sites having the fastest Late Pleistocene and Holocene uplift rates spatially coincide.
Lambeck et al. (2004) published a review of the last 12 kyr relative sea-level changes in Italy and used the elevation of the LIg marker as a benchmark to assess tectonic stability at individual coastal sites. Most of the 27 sites investigated by Lambeck et al. (2004) were located along tectonically stable coasts. A more comprehensive review of the Holocene displacement was provided by Antonioli et al. (2009), using more than 100 sites in stable, uplifting and subsiding regions. Antonioli et al. (2009) afforded a first comparison with intermediate-scale rates provided by published and new LIg markers, and with instrumental record provided by tide-gauges and levelling measurements in Calabria and NE Italy. A more updated compilation has been presented by Lambeck et al. (2011) using improved glacio-hydro isostatic model parameters. Differences between observed and predicted sea level changes were interpreted as reflecting Late Holocene vertical tectonic contributions at more than 456 sites (211 for the Holocene and 255 from the LIg).
These review works on Holocene displacement have estimated the averaged tectonic motion, but have not assessed whether different sources (e.g. due to regional or local processes) contribute to displacement. Only in few case-studies in the Calabrian arc (de Guidi et al., 2003; Ferranti et al., 2007; Scicchitano et al, 2011) it was possible to quantify the contribution of stick-slip, co-seismic displacements versus regional, steady displacement.