Earthquakes and ghost towns in Sicily: from the Valle del Belìce in 1968 to the Val di Noto in 1693. The first stage of the virtual seismic itinerary through Italy

Destructive earthquakes leave traces not only on the physical landscape but also on human processes. Among the most devastating consequences is the abandoning of towns and villages, in favour of locations deemed safer. Abandoning a village and resettling in a new location, whether a gradual process or the result of a sudden traumatic situation, is an event of great historical, cultural and anthropological impact. It entails the loss of a piece of history or culture – local identity – and the more suddenly it happens, the more dramatic the after-effects. Italy has almost two hundred localities that have been abandoned for different causes (landslides, floods, volcanic eruptions, but also social or environmental reasons), some ninety of them owing to earthquakes. Sicily, a land of volcanoes and earthquakes, has several traces of former villages either in the form of fairly substantial ruins or even half-destroyed, which are usually located a few kilometres away from the new settlements. In this paper, we present the methodological approach developed in the framework of the EDURISK Project to enhance the awareness of seismic risk as an element of daily life; the case-study of the Valle del Belìce after the 1968 earthquakes represents the richness and complexity of this approach well. Following this rationale, in 2006, we published the first multimedia product devoted to Sicily based on the tools available at that time: a DVD-Rom hosting the interactive Quick TimeTM Virtual Reality format. Today, multimedia technology is much more advanced and web- oriented, but the methodological approach is still valid

Estimating the expected seismicity rates of volcano-tectonic earthquakes at Mt. Etna (italy) by a geometric kinematic approach

Seismic hazard studies have been undertaken at Etna volcano in the last years with the aim of estimating the potential of local fault’s activity in generating destructive earthquakes. The target is the mid-term assessment (30, 20, 10 and 5 yrs), as the identification of zones that are exposed to the recurrent seismic shaking may be important for land planning at a local scale, and it represents a valuable complement to establish priority criteria for seismic risk reduction action. The methodologies applied at Mt. Etna area include probabilistic approaches based on the use of historical macroseismic data (the “site approach” by the software code SASHA, see Azzaro et al., 2008) and fault-based time-dependent models in which occurrence probabilities of major earthquakes are estimated through the Brownian Passage Time (BPT) function and the time lapsed since the last event (Azzaro et al., 2012b, 2013b). Mean return period of major earthquakes - strong to destructive events with epicentral intensity I0 ≥ VIII EMS, considered as “proxies” of “characteristic” earthquakes – have been obtained by the fault seismic histories, i.e. the associations “earthquake-seismogenic fault” derived from the historical catalogue of Etnean earthquakes (CMTE Working Group, 2014). Inter-time statistics of major earthquakes have been applied to the Timpe tectonic system, considered as a homogeneous seismotectonic domain (Azzaro et al., 2013b), obtaining a mean recurrence time (Tmean) of 71.3 years, and an aperiodicity factor α (σTmean/Tmean) = 0.42, typical of semi-periodic processes. In the present study we present the preliminary results of an analysis aimed at verifying the variability of the mean occurrence times of major earthquakes generated by the main tectonic systems at Etna (Pernicana and Timpe faults) by using a geological approach based on geometrickinematic parameters (3D dimensions, slip-rates etc) representative of fault activity. Method and input data

Probabilistic seismic hazard assessment in the Mt. Etna region (Italy): application to local volcano-tectonic earthquakes

Earthquakes are, by far, the most relevant source of hazard for the densely urbanised areas of Mt. Etna region. Local communities living in the eastern and southern flanks of the volcano continuously suffer social and economic losses due to the very high occurrence of damaging earthquakes, which produce intensities up to degree X EMS despite of low energy (M < 5.0). Seismic hazard in the Mt. Etna region is controlled by two distinct types of earthquakes, namely regional and local events, which have different magnitudes and frequencies (Azzaro et al., 2008). In particular, hazard deriving from local volcano-tectonic events can be relevant if short exposure times (30 years) are considered, since the reference intensity (Iref) calculated at the exceeding probability of 10% reaches, in some localities, the IX degree (Azzaro et al., 2008; Azzaro et al., 2013). In the framework of the UPStrat-MAFA project, the seismic hazard was performed following the probabilistic approach (PSHA) based on historical macroseismic data, by using the SASHA code (D'Amico and Albarello, 2008; Albarello and D’Amico, 2013) which has been implemented in the project itself. This approach uses intensity site observations to compute the seismic history for each investigated locality; results are obtained in terms of maximum expected intensity with an exceedance probability ≥ 10% for a given exposure time. In this study we produced PSHA maps referred to local volcano-tectonic seismicity

A Reappraisal of the 1968 Valle Del Belice Seismic Sequence (Western Sicily): A case study of Intensity Assessment with Cumulated Damage Effects

In 1968, six earthquakes with magnitude between 5.1 and 6.4 destroyed or heavily damaged several towns in the Valle del Belìce(western Sicily), causing some three hundred fatalities. There have been some critical issues in the intensity assessment however in the macroseismic studies produced over the years , since the MCS scale was used as an estimation of shaking rather than a representation of the damage scenario; in practise, intensity was assigned for each earthquake of the sequence disregarding the effect of the cumulative damage. The case-study of the 2016-17 earthquakes in Central Italy reflected the difficulty in estimating the intensity in localities repeatedly hit by strong shocks, producing macroseismic parameters (epicentre, magnitude) inconsistent with the instrumental ones. As for the 1968 Valle del Belìcesequence, the Parametric Catalogue of Italian Earthquakes CPTI15 reports the macroseismic parameters, owing to the inadequacy of the seismic network operating in Italy in that period. Aware of the issues related to epicentre locations and magnitudes calculated by the existing macroseismic datasets, here we propose a reappraisal of the 1968 earthquakes following a methodology tested during the 2016-17 seismic sequence in Central Italy. By a new analysis of the primary sources, we reconstruct the evolution of the damage scenario during the sequence and assess intensity by using the European Macroseismic Scale EMS-98; the new macroseismic parameters are finally compared with the ones of the CPTI15 catalogue. Lastly, we propose a procedure for minimizing the magnitude overestimation in case of seismic sequences, based on the computation of the total seismic moment M0

Stick-slip vs. stable sliding fault behaviour: A case-study using a multidisciplinary approach in the volcanic region of Mt. Etna (Italy)

Abstract In active volcanic zones, fault dynamics is considerably fast but it is often difficult to separate the pattern of nearly continuous large-scale volcanic processes (inflation/deflation processes, flank instability) from impulsive episodes such as dyke intrusions or coseismic fault displacements. At Etna, multidisciplinary studies on active faults whose activity does not strictly depend on volcanic processes, are relatively few. Here we present the case-study of the San Leonardello fault, an active structure located in the eastern flank of Mt. Etna characterised by a well-known seismic history. This fault saw renewed activity in May 2009, when pre-seismic creeping along the southern segment preceded an MW 4.0 earthquake in the northern segment, followed by some twenty-five aftershocks. Later, in March–April 2016, creep events reactivated the southern section of the same fault. Both the seismic and aseismic phenomena were recorded by the seismic and GNSS networks of INGV-Osservatorio Etneo, and produced surface faulting that left a footprint in the pattern of ground deformation detected by the InSAR measurements. We demonstrate that the integration of multidisciplinary data collected for volcano surveillance may shed light on different aspects of fault dynamics, and allow understanding how coseismic slip and creep alternate in space and time along the strike. Moreover, we use findings from our independent datasets to propose a conceptual model of the San Leonardello fault, taking into account behaviour and previous constraints from fault-based seismic hazard analyses. Although the faulting mechanisms described here occur at a very small scale compared with those of a purely tectonic setting, this case-study may represent a perfect natural lab for improving knowledge of seismogenic processes, also in other fault zones characterised by stick slip vs. stable-sliding fault behaviour

“Knowledge and practice”. Educational activities for reduction of earthquake impact: the EDURISK project

The EDURISK project (Earthquake eDUcation: a journey for seismic RISK reduction) focuses on the development of educational tools and activities centred on earthquakes and the mitigation of seismic risk, for use in courses and campaigns for seismic risk reduction addressed to students of age 4-13 and to adults and on their hand-on experimentation in targeted areas. The project aims to improve the general awareness of seismic risk by disseminating reliable information tailored to the needs, interests and learning abilities of a large and varied public. An efficacious strategy for seismic risk mitigation addressed to the general public must involve all the aspects of human life that are under seismic risk. Earthquakes should be presented not only as physical and geological phenomena but also as social events interacting with people’s lives and belongings. The EDURISK project should be perceived as a joint venture between the world of scientific research and the world of basic schoolteaching, working together to build up awareness and knowledge useful to reduce the seismic risk

Impacts of the 1669 eruption and the 1693 earthquakes on the Etna Region (Eastern Sicily, Italy): An example of recovery and responses of a small area to extreme events

In this paper we trace the impact of the 1669 eruption and the 1693 earthquakes in eastern Sicily, their effects on the people living in the Etna region and, more particularly, in the city of Catania and its hinterland. The former event was the largest historic eruption of Etna, having a flow field with an area of ca.40 km2 and a maximum flow length of ca. 17 km, whereas the latter - occurring only 24 years later - killed between 11,000 and 20,000 of Catania’s estimated 20-27,000 inhabitants, plus many more in smaller settlements. Using a combination of field-based research, contemporary accounts and archival sources, the authors are able to draw a number of conclusions. First, the 1669 eruption, although it did not kill or injure, was economically the most devastating of historical eruptions. Although it affected a limited area, inundation by lava meant that land was effectively sterilized for centuries and, in a pre-industrial agriculturally-based economy, recovery could not occur quickly without outside assistance from the State. Indeed some of the worst affected municipalities (i.e. Comuni) were only able to support populations that were much reduced in size. Secondly, much of the damage caused to buildings by volcanic earthquakes was effectively masked, because most of the settlements affected were quickly covered by lava flows. The vulnerability to volcanic earthquakes of traditionally constructed buildings has, however, remained a serious example of un-ameliorated risk exposure through to the present day. A third conclusion is that the 1693 earthquakes, although more serious with respect to the number of people and the area they affected in terms of mortality, morbidity and their immediate economic impact, saw a rapid and sustained recovery. This was due in part to the fact that, in contrast to lava flows, an earthquake does not sterilize land, but more significant was the reduction in population numbers which served both to release and concentrate funds for investment in recovery. By the close of the eighteenth century Catania was known throughout Europe for the quality of its townscape and buildings, many of which were constructed in the then fashionable (and expensive) baroque style. Finally, the 1669 and 1693 disasters were seized on by the authorities as opportunities to plan new and re-build old settlements with improved infrastructure to facilitate economic growth. By the nineteenth century many of the lessons had been largely forgotten and there were many examples of: poor seismic design of individual buildings; and the location of new residential and commercial areas that placed more people at greater risk from future extreme events. Indeed it is only recently have new regulations been enacted to prevent the construction of buildings in the vicinity of active faults and to control development in other hazardous zones

Applying the Disruption Index procedure to evaluate the urban seismic risk in the Mt. Etna area (Italy)

The Disruption Index is used here for the assessment of urban disruption in the Mt. Etna area after a natural disaster. The first element of the procedure is the definition of the seismic input, which is based on information about the historical seismicity and seismogenic faults. The second element is the computation of the seismic impact on the building stock and infrastructure in the region considered. Information on urban-scale vulnerability was collected and a geographic information system was used to organize the data relating to buildings and network systems (e. g., typologies, schools, strategic structures, lifelines). The central idea underlying the definition of the Disruption Index is the identification and evaluation of the impacts on a target community, considering the physical elements that contribute most to the severe disruption. The results of this study are therefore very useful for earthquake preparedness planning and for the development of strategies to minimize the risks from earthquakes. This study is a product of the European “Urban Disaster Prevention Strategies using Macroseismic Fields and Fault Sources” project (UPStrat-MAFA European project 2013).PublishedTorino, Italy3T. Pericolosità sismica e contributo alla definizione del rischioope

The 2015 version of the Italian Parametric Earthquake Catalogue (CPTI15)

The Italian Parametric Earthquake Catalogue (CPTI) represents the most extensive and reliable source of parameters for earthquakes in Italy and surrounding areas. Since its first introduction in 1999, CPTI benefits from the results of the 30-years-long Italian tradition in historical earthquake research that, still today, keeps on providing a wealth of studies and macroseismic data. Such data have been collected, homogenized and made available through several releases of the related macroseismic database (DBMI). In 2016, the fourth release of CPTI and DBMI, has been finalized. They provide the most advanced and updated sets of macroseismic and instrumental data and parameters, and cover the time-span 1000-2014 with earthquakes with maximum intensity I ≥ 5 or magnitude Mw ≥ 4.0. The catalogue lists 4574 events, 70% of which accompa- nied by intensity data points (about 125’000 as a whole). Macroseismic data derive from 185 studies, 54 of them are new with respect to the previous version CPTI11. Parameters related to historical earthquakes are completely re-assessed, and magnitudes from macroseismic data are derived with new intensity-to-Mw relationships. Such relationships are based on the same dataset that contributes updated instrumental magnitudes to the catalogue. Either Mw from moment tensor solutions or proxies calculated with new published conversion relationship are considered. If available, both macroseismic and instrumental parameters are provided, together with a set of “preferred ones”, which consist of a selection between the macroseismic and the instrumental epicentres, and the weighted average of the macroseismic and instrumental magnitudes.PublishedTrieste, Italy3T. Storia Sismica4T. Sismologia, geofisica e geologia per l'ingegneria sismica4IT. Banche dat

On assessing importance of components in dysfunction urban systems given an earthquake: the case of Mt. Etna region

Mt Etna region (Sicily, Italy) is one of the test areas studied in the European Project “Urban disaster Prevention Strategies using MAcroseismic fields and FAult sources” ( UPStrat-MAFA) to which the methodology of Disruption Index (hereafter DI), recently developed to evaluate the dysfunction of urban systems caused by earthquakes (Ferreira et al., 2014), has been applied on a trial basis