Maria Serafina Barbano

Discrimination of Tsunami Sources (Earthquake versus Landslide) on the Basis of Historical Data in Eastern Sicily and Southern Calabria

Abstract The source mechanisms responsible for large historical tsunamis that have struck eastern Sicily and southern Calabria are a topic of robust debate. We have compiled a database of historical coeval descriptions of three large tsunamis: 11 January 1693, 6 February 1783, and 28 December 1908. By using accounts of run-up and inundation and employing an approach proposed by Okal and Synolakis in 2004, we can provide discriminants to define the nature of the near-field tsunami sources (fault dislocation or landslide). Historical reports for the 1908 event describe affected localities, maximum run-ups, and inundation areas. However, for the 1693 and 1783 tsunamis, reports are limited to inundation and occasional run-up estimates. We calculate run-up values for these events using available relations between inundation and run-up. We employed the model of Okal and Synolakis to the obtained profiles of tsunami run-up along the inundated shorelines. The 1908 run-up data distribution confirms that the tsunami is compatible with a seismic dislocation source, whereas the 1783 data supports contemporary observations and recent offshore investigations suggesting that the tsunami was produced by an earthquake-triggered submarine landslide. Analysis of the 1693 event data suggests that the tsunami was generated during a tectonic event and thus a seismogenic source should be found offshore.

Geological evidence of paleotsunamis at Torre degli Inglesi (northeast Sicily)

[1]xa0Two layers of fine sand of marine origin occur in a sequence of organic rich colluvia in an archaeological excavation at Torre degli Inglesi, on Capo Peloro, northeast Sicily. Stratigraphic and micropaleontologic analyses support the hypothesis that these layers are related to deposition due to paleotsunami waves. Their ages are constrained both with radiocarbon and archaeological datings. The age of the oldest layer is coincident with the 17 A.D. earthquake that hit Reggio Calabria but for which no tsunami was previously reported. The age of the youngest layer can be only constrained in the range 3rd–19th century and is tentatively associated to the 6 Feb. 1783 event.

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.

The Pollina (northern Sicily-Italy) earthquake of 26 June 1993: an application of the new European Macroseismic Scale 1992

The new European Macroseismic Scale 1992 (EMS) is applied to intensity estimation of data collected in field investigations of the 26 June 1993 Pollina (northern Sicily) earthquake and the results are compared with those obtained using the MSK-81 scale. The highest intensity estimated (VI–VII) fits with the low magnitude value (ML = 4.7) and the low resistance level of buildings is responsible for some unexpected severe damage, thus raising the seismic vulnerability of the area. The tectonic framework shows significant elements of recent activity accounting for the frequent seismicity. The study also evaluated the validity of using vulnerability classes of buildings as defined in the EMS scale in the intensity assessment of historical earthquakes of the area.

EARTHQUAKE DAMAGE SCENARIOS AND SEISMIC HAZARD OF MESSINA, NORTH-EASTERN SICILY (ITALY) AS INFERRED FROM HISTORICAL DATA

A study aimed at evaluating earthquake damage scenarios and seismic hazard of Messina using historical data, is presented. The analysis of coeval reports allowed us to reconstruct the seismic history of the city and to obtain a homogeneous earthquake site catalogue based on intensity assessed by the European Macroseismic Scale 1998. In the last 1200 years Messina was destroyed once (1908, intensity X-XI EMS) and suffered effects estimated between intensities VII and IX EMS many times (e.g. 853, 1169, 1494, 1509, 1599, 1693, 1783, 1894, 1909). Destruction or severe damage which affected the city are mainly related to earthquakes occurring in the Messina Straits and Southern Calabria, while slighter, moderate effects are usually due to shocks taking place in the seismogenic sources of SE Sicily, Gulf of Patti and Northern Calabria. The damage scenarios of the most relevant events, delineated using coeval urban plans of the city, showed that damage distribution is strongly conditioned by the different soil response. A probabilistic seismic hazard assessment was obtained by using site observed intensities: The expected intensity in a time span of 50 years (i.e. maximum intensity characterised by at least 10% exceedance probability in 50 years) is DC EMS; the expected intensity in a time span of 300 years (10% exceedance probability in 300 years) is X EMS.

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.

Study of landslides at the archaeological site of Abakainon necropolis (NE Sicily) by geomorphological and geophysical investigations

This paper reports on the investigation of the old landslide body on which the necropolis of Abakainon, an Italian archaeological site, was built about 2400xa0years ago. This site is located in a geologically complex area of northeastern Sicily, where active tectonics has strongly modified the morphological landscape, as testified by the meandering path of watercourses, widespread presence of paleosurfaces, and deviations of crest line. Previous studies have hypothesized that the necropolis, suddenly destroyed by a catastrophic event in historical times, could have been built on an old landslide body. This represents the starting point of this paper, focused on geomorphological analysis and geophysical surveys, which allowed discovering peculiar elements in support of the landslide theory. In particular, the elaboration of a Digital Terrain Model allowed locating the main morphostructural elements, thus highlighting how the occurrence of landslides in the study area is strongly linked to recent tectonics. Passive seismic surveys, carried out through the acquisition of ambient noise, allowed detecting the presence of impedance contrasts, which were associated to peculiar features, such as the landslide body itself. Moreover, local strong directional effects testify the presence of faults, affecting even the necropolis area. Such results, further corroborated by the outcomes of an electrical resistivity survey, lay the foundations for interesting consideration on the possible cause of the destruction of this site, probably related to the occurrence of a historical earthquake in the first century AD.

Was the ancient harbour of Catania (Sicily, southern Italy) buried by medieval lava flows?

The question about the existence of an ancient harbour at Catania is a matter of debate between ancient and modern scholars. No decisive information has been found so far, although numerous hypotheses have been proposed in literature. Since the fifth century BC, historians have documented that numerous naval armadas landed in the port of Catania. However, the current morphology of the Catania coastline has not any protected inlet that could have offered a shelter to hundreds of ships. Starting from historiographical descriptions of the Catania harbour and of the different lava flows occurring since 2500 BC, we sought to infer the most probable area of landing. To address this purpose, literary sources and historical iconographic documentation, combined with geological data and archaeological records, were collected and analysed, in order to verify whether historical documents were consistent with the palaeotopography of the area. The analysis suggests that the main harbour of Catania was probably located north-east of the town, between the S. Giovanni Li Cuti inlet and the Ognina bay, before being filled with some medieval lava flows (during 1100–1400 AD). The apparent silence of the local historical sources on the destruction of the port may well be related to the 1169 earthquake that devastated Catania (causing 15,000 fatalities) and a large part of eastern Sicily. It is therefore likely that the few survivors paid little attention to the lava flow invading the harbour.

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.