Vladimiro Verrubbi

Holocene sea-level change in Sicily and its implications for tectonic models: new data from the Taormina area, northeast Sicily

The northeast coast of Sicily shows emergent marine features that have been uplifting during the Holocene along the footwalls of two major regional fault systems, the Malta Escarpment and Messina fault system. Previously, uplift rates were interpreted as up to about 1.8 mm/mm a−1. New dates on shelly remains, collected close to sea-level, from the Taormina area north of Mount Etna, and amended sea-level curves, are used to show that uplift over the past 6000 years has been proceeding at a slower rate of about 1.4 mm a−1. However, over a longer time period, from the Tyrrhenian Oxygen Isotope Stage 5.5 (about 125 ka) to the present day, the uplift rate has been yet slower, at about 1 mm a−1. Northeast Sicily lies in a complex plate boundary region whereas, in contrast, the rest of Sicily appears to have been stable throughout the later Quaternary. Further comparisons show that the French Mediterranean coast [Lambeck, Bard (2000) Earth Planet. Sci. Lett., 175, 202–222] is a region of crustal stability, where movement is dominated by subsidence of the outer portion of the proglacial forebulge of the last glaciation. There the coastline has been progressively submerged during the Holocene, and sea level has never been higher than at present. Northeastern Sicily uplift is therefore more likely controlled by plate processes that mask most of the effects of glacio-hydro-isostatic adjustment.

The RUSLE erosion index as a proxy indicator for debris flow susceptibility

Debris flows represent dangerous occurrences in many parts of the world. Several disasters are documented due to this type of fast-moving landslides; therefore, natural-hazard assessment of debris flows is crucial for safety of life and property. To this aim, much current work is being directed toward developing geotechnical-hydraulic models for the evaluation of debris flow susceptibility. A common base for such current models is parameterization of background predisposing and triggering factors such as inherent characteristics of geo-materials, topography, landscape and vegetation cover, rainfall regime, human activities, etc. which influence the occurrence of these processes on slopes. The same factors are also taken into account in soil erosion prediction models. Consequently, it seems worth investigating the effectiveness of the soil erosion index as debris flows susceptibility indicator. To this aim, a logistic regression analysis was carried out between the erosion index assessed by means of the Revised Universal Soil Loss Equation (RUSLE) model and the inventory of debris flows that have occurred in an area in Sicily (Southern Italy). Model assumptions were verified and validated by means of a series of statistical tools. Different possible scenarios were also evaluated by considering hypothetical changes in soil erosion rate under different rain erosivity conditions. Notwithstanding the rough approximations in model data collection, the outcomes appear encouraging.

Rockfalls Monitoring Along Eastern Coastal Cliffs of the Favignana Island (Egadi, Sicily): Preliminary Remarks

Favignana island (Sicily, Italy) is a historical and environmental attraction site frequented by tourists during the long warm season of the year. For several centuries the calcareous sandstone outcropping in the east side of the island has been extracted and used as building stone. Actually the quarries and the caves are undergoing to erosional and gravitational processes that are influencing the touristic use. As well as putting at risk the safety of people attending the area, the diffused rock falls are likely to jeopardize sites of great anthropological value that, once destroyed, can no longer be reconstructed. An integrated monitoring project of the cliffs is aimed to identify the most active areas and to provide support to the local government’s policies in the implementation of mitigation measures. If adequate measures will be taken in the future, operators and users of the tourist circuit will have the opportunity to enjoy these amazing areas with lower level of landslide risk.

Susceptibility to Sea Cliff Failures at Cala Rossa Bay in Favignana Island (Italy)

Since the Roman Age and until the last century, an intense quarry activity took place at Favignana Island (Sicily, Italy) that significantly changed the morphology of the eastern part of the Island that is characterized by sea cliffs. This mining activity produced an extensive network of open air quarries, underground quarries and tunnels, locally named “Pirrere”, that are hosted into Pleistocene calcarenites. The sea cliffs of the eastern coast of Favignana Island were also influenced by the past mining activity and they are currently affected by diffused instabilities as proved by the wide block-size talus distributed all along the coast. A more detailed slope stability analysis was performed on a sea cliff located in the western sector of Cala Rossa Bay. To constrain such an analysis, engineering-geological field and remote surveys were carried out to reconstruct the geological setting as well as to characterize the mechanical properties of the rock mass. Finally a 3D model of the joints net was obtained. Based on geometrical and geomechanical joints features, a kinematic-compatibility analysis for rock landslide mechanisms (i.e. planar sliding, wedge sliding and toppling) allowed to identify 78 rock blocks particularly prone to failure. Considering hydrostatic pressure related to joints saturation condition as well as pseudostatic forces due to earthquake, 12 hazard scenarios were considered as reliable for the sea cliff area. The obtained results demonstrate that: (i) planar and wedge sliding are more suitable landslide mechanisms respect to toppling; (ii) the SE part shows higher susceptibility to failures; (iii) water pressures within joints play a more destabilizing action respect to earthquakes. Such an analysis represents a preliminary contribution to manage protection strategies for reducing the landslide risk in the touristic site of Cala Rossa bay and to preserve the unique heritage of the “Pirrere” quarries.

The Experience of Seismic Microzonation in Lazio Region (Italy) Mountain Municipalities

Within the activities of seismic microzonation promoted and co-funded by Lazio Regional Administration (LRA) and the Department of Civil Protection (DPC), following the issues of the National rule OPCM 3907/2010, seismic microzonation studies were carried out in a set of municipalities, already attributed to the seismic Zone 1 (i.e. with the most severe level of seismic hazard and located in mountain areas). These municipalities show similar geologic and geomorphologic features as they are characterized by a local bedrock constituted of limestone and marly-limestone and fluvial-lacustrine deposits filling intra-mountain alluvial plains. The engineering-geological model of the subsoil as well as the jointing conditions of the outcropping rock masses were defined on the basis of available technical data from public reports, as well as from original geophysical surveys. Different types of microzones (i.e. stable, stable susceptible to seismic amplification and unstable areas) were identified according to the technical rules (ICMS 2008). Nevertheless, the experienced approach highlighted some critical features in the microzonation methodology that encourage future studies devoted to obtain the refinement of the operative procedures.

Studies of seismic microzonation in Latium region (Italy) by experiencing the application of official guidelines in intra-mountain plains

In 2010, the Latium Regional Administration promoted a systematic study for the seismic microzonation of its Municipalities, according to the official national and regional guidelines. This activity was co-funded by the National Department of Civil Protection (DPC) following the issue of the National rule OPCM 3907/2010. A Working Group including researchers from Latium Regional Administration, ENEA and the Department of Earth Sciences of the ‘Sapienza’ University of Rome performed the studies in some municipalities characterised by the most severe level of seismic hazard. The activity was carried out on the basis of both archive geotechnical data and original geophysical surveys. The whole municipal territory was divided in stable areas, where no further analysis is required, and areas prone to stratigraphic or topographic amplification, as well as to earthquake-induced phenomena such as landslides, sinkholes, liquefaction and seiche. The experienced approach highlighted some critical features in the microzonation methodology that encourage the refinement of the operative procedures.