Concluding remarks

This review illustrates how the use of various analytical tools in the study of coastal tectonics in Italy may provide information on specific time intervals and acting processes, with variable accuracy and precision. We recognize that uplift rates computed from the LIg marker are average estimates since 125 kyr BP, and do not show the temporal variability that might have occurred during individual earthquake cycles, which act at the 1-10 kyr interval, or, in the case of volcanic deformation, during episodes of magmatic unrest. In addition, long-term markers do not establish whether a particular site is currently experiencing tectonic stability or deformation. This alternative occurrence must be checked using younger markers (i.e. Holocene geomorphological and geoarcheological markers), or instrumental data. However, determination of Holocene displacement is difficult for most sites in Italy because of observational limitations imposed by the low displacement accrued since. Thus, the LIg markers remains for most of the Italian coastline an unsurpassed tool for reconstruction of the recent vertical tectonic motion.

On the other hand, when favourable conditions ensue, it is only the Holocene markers that provide insights into the current (1-10 kyr) earthquake cycle or, in the case of volcanic deformation (e.g. Campania), into transient processes such as magma injection, withdrawal, and depressurization. Unfortunately, the occurrence of ancient co-seismic events using Holocene geomorphological data has to date been proved only for an handful of sites in southern Italy and Sicily (Mastronuzzi and Sansò, 2002; de Guidi et al., 2003; Ferranti et al., 2007; Scicchitano et al., 2011). Everywhere else, studies of Holocene coastal displacements have solely provided average displacement rates. Compared to the 100 kyr scale indicators, Holocene markers yield a higher precision (inherent in recognition and measurement of markers), but suffer of less accuracy. This stems from the concurrence of other, non-tectonic processes (sediment compaction, non-modelled GIA effects, and so on) in the displacement budget, which, on the contrary, are averaged out when the LIg data are used.

Finally, instrumental data, both CGPS and tide-gauges, provide the most positive evidence of active deformation, but are fewer and have so far lesser accuracy than Holocene data, a pitfall which will be surpassed as time series grow. Data mass enlargement will also permit to model more adequately transient processes (e.g. oceanographic perturbations for tide gauges and silent slips for GPS data) which in many cases are still embedded in the presently available signal.