Claudia Pirrotta

Landslide triggers along volcanic rock slopes in eastern Sicily (Italy)

A new dataset of landslides, occurred in a tectonically active region, has been analysed in order to understand the causes of the slope instability. The landslides we have dealt with took place along the volcanic rock cliff of S. Caterina and S. Maria La Scala villages (eastern Sicily, Italy), a densely inhabited area located on the eastern margin of Mt. Etna, where some seismogenic faults, locally named Timpe system, slip during moderate local earthquakes and also move with aseismic creep mechanisms. The results show that landslides are triggered by heavy rainfalls, earthquakes and creep fault episodes. Indeed, they occur along discrete fault segments, exhibiting a combination of both brittle failure, indicated by the earthquake occurrence, and aseismic creep events. The analysis of seismicity occurred on the Timpe fault system has shown that the active Acireale fault, in its southernmost segment, is subject to an aseismic sliding, which increases after the stick–slip motion in the nearby faults. Therefore, aseismic creep seems to concur in the predisposition of a rock to fail, since strains can increase the jointing of rock masses leading to a modification in the slope stability. Understanding the factors concurring to the slope instability is a useful tool for future assessments of the landslide hazard in densely settled areas, located on a volcanic edifice, such as Etna that is slowly sliding seawards, and where active faults, seismicity and heavy rains affect the deeply fractured slopes.

Evidence of active tectonics in southern Calabria (Italy) by geomorphic analysis: the examples of the Catona and Petrace rivers

This work integrates new detailed geomorphic analyses of the Petrace and Catona fluvial network (southern Calabria) with structural geology data in order to characterize the activity of the fault systems intercepting the fluvial basins and to constrain the seismotectonic setting of the study area. Several strong earthquakes (Maw 6.0-7.1) occurred in the last millennium in the area, which is considered among the most seismically active zones in Italy. However, the lack of instrumental data for strong historical earthquakes and the poor exposure of faulted Quaternary sediments, do not allow the easy identification of active, seismogenic faults. We mapped known faults and new minor structures, transversal and parallel to the master faults, through aerial-photo interpretation and DEM analysis. The transversal structures are minor faults and connecting faults accommodating movement between the master faults that slipped generating strong destructive historical earthquakes. The geomorphological analysis highlights markers of recent tectonic activity associated to the mapped faults. Hierarchical parameters and geomorphic indexes of the Petrace and Catona Rivers show drainage anomalies due to active tectonics and reveal the activity of the faults intercepting them. This work shows that, in southern Calabria, besides the known master faults associated with some catastrophic historical earthquakes, minor faults are active and could be sources of low magnitude seismic release. Finally, the geomorphic and geomorphological analyses allow reconstructing the evolution of the Petrace and Catona rivers and fault activity and dating to Late Pleistocene the present day Messina Strait graben configuration.

Paleoseismic Investigation of Historical Liquefactions Along the Ionian Coast of Sicily

Eastern Sicily is an area where some of the most catastrophic earthquakes in Italian history occurred. As reported by historical sources, these earthquakes induced liquefaction phenomena. In two areas along the Ionian coast of Sicily we found liquefaction evidence in Holocene deposits. In the Minissale site (east of Mount Etna), the observed liquefaction features can be related to the 1169 and 1693 earthquakes, while in the Agnone site (south of Catania), the deformational structures can be tentatively associated to the 1542 and 1693 events. Both sites locate in areas where historical liquefaction has been observed in the past, thus confirming the actual liquefaction susceptibility/potential in this region. The evidence of repeated liquefaction events at the same site, highlights the relevance of the paleoseismic approach for modeling the recurrence time and preparing scenarios of seismic effects in eastern Sicily, where seismogenic sources are scantly defined.

A Reappraisal of Seismicity and Eruptions of Pantelleria Island and the Sicily Channel (Italy)

Three main tectonic depressions (the Pantelleria, Linosa and Malta troughs), the expression of a continental rift, characterize the Sicily Channel, a region with recent volcanic activity attested by the Pantelleria and Linosa volcanic islands, as well as numerous seamounts. To understand the seismic and eruptive behaviour of this area, we compare historical and instrumental seismicity retrieved from catalogues with recordings from both a mobile seismic network and a permanent station deployed at Pantelleria. A review of historical eruptions affecting the Sicily Channel is also presented. Recent instrumental seismicity shows that the Sicily Channel is characterized by a low level of seismicity, with earthquakes mainly occurring as isolated events, rather than swarms as observed during the few documented eruptive periods. The results of a seismic survey in 2006–2007, as well as the signals recorded by a permanent station in 2010–2014, enable stating that also Pantelleria is characterized by a very low rate of seismicity. The available, though scant, historical information suggests a recurrence time of about a century for the volcanic activity and that eruptions are usually preceded by seismic swarms. In the only historical known eruption of Pantelleria, in addition to shocks, uplifting and increasing fumarole activity, were observed. Notwithstanding the lack of eruptions over the past century, and despite the low recent seismic rate, we believe that the geophysical monitoring of the Sicily Channel needs improving since it is an area of potentially high seismic and volcanic hazard given the presence of several active submarine eruptive centres.