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On October 12, 2013 an earthquake with Mw=6.5 occurred in the southern Hellenic Arc, about 20km off the west coast of Crete. The mainshock, whose focal depth is of the order of 40km, was followed by aftershocks felt in the nearby cities and villages, even though the aftershock sequence was rather poor. The epicenter is located at about 60 km from the CRE receiver of the European VLF/LF Radio Network. Some day before the earthquake a clear disturbance appeared in one of the ten radio signals sampled by the CRE receiver . The disturbance, considered as an anomaly, appears in the 216 kHz radio signal radiated by the transmitter MCO that is the main broadcasting facility for long and medium wave broadcasting of Radio Monte Carlo near Roumoules, France. The site is an exclave of Monaco and extraterritorial area. The signal radiated by MCO transmitter can be well received, mainly at night time, in whole Europe. The radio path MCO-CRE crosses exactly the epicenter area of the previous earthquake. Here we present a detailed study of the anomaly by means of statistical and spectral tools and analyze also the behavior of other sampled radio signals in the European network, and take into account other possible causes of disturbances. We conclude that the possibility that the disturbance in the MCO radio signal is a precursor of the earthquake is rather convincing., peer-reviewed

The evaluation of the expected peak ground motion caused by an earthquake is of great importance in seismicity and earthquake engineering studies. In the present study, weak-motion data related to small earthquakes are used, in order to extrapolate peak ground motion parameters beyond the magnitude range of the weak-motion dataset, on which they are calculated. A complete description of the seismic ground-motion characteristics in the Gulf of Corinth region in Greece is provided, with parameterization of the attenuation of seismic ground motions with distance and their variability in excitation with earthquake magnitude. We use over 1000 earthquakes recorded at the Hellenic Unified Seismic Network (HUSN) with magnitudes larger than 2.5 ML. Following a regression analysis of this large number of weak-motion data, we determine a frequency-dependent crustal quality factor, a geometrical spreading function and the absolute source scaling. In order to calibrate sufficiently the source scaling, it is necessary to use the available moment magnitude values of events from the selected dataset. The National Observatory of Athens Moment Tensor Database (NOA-MTs) is used, which includes 52 events in the range 3.3 to 5.4 MW for the time period in analysis. Complementary, we calculate moment tensor solutions with high-quality for small events not included in the NOA-MTs catalogue, using the 'Cut And Paste' technique. Results on region-specific crustal attenuation and source scaling, together with the effective duration of seismic ground motion in the region, are used to estimate the peak ground motion parameters, such as PGA, PGV, and SA at different frequencies. Using stochastic ground motion simulations, we predict the absolute level of ground shaking and compare them with strong motion data in the region. The attenuation of simulated ground motion is compared with recent global and regional ground motion prediction equations (GMPEs). The performance of the stochastic model is also tested against moderate sized earthquakes (~5-6 MW) recorded by HUSN in the area under study., peer-reviewed

About two centuries ago, the Earth entered the Anthropocene, a new geological epoch in which man has a marked impact on climate and the environment. In comparison with the slow passing of previous millennia, our species has, in a very short time, radically altered the world's ecosystems. For some years now, interest in Italy has been increasing in Geoethics and the ethical, sociological and cultural implications of Earth Sciences. This involves amplifying the prospects and expectations of Geosciences and highlighting the fundamental role of geological and geographical studies in finding solutions to the practical problems that man faces which are also compatible with the preservation of nature and the planet. Indeed, man can even be an active participant in natural catastrophes in the sense that he is able to amplify the damage and natural dynamics. On the other hand, as much as these phenomena can only be foreseen to a limited extent, intervention is possible with regards the parameters of risk which are dependent upon anthropisation, such as those of vulnerability and exposed value that mark the difference between a natural event and a calamity. Therefore, through information about and knowledge of risk, it is possible to keep damage to a minimum by refining techniques of prevision and prevention. Geographical studies orientated towards examining descriptive natural elements and analysing social behaviour when people are faced with natural risks generated by assumed given and exogenous sources can be historically placed within the area of research into the perception of natural risk. In this context, a questionnaire was given to primary and middle school pupils in an area of Calabria which has recently been affected by an on-going seismic sequence, widely felt by the population. The same questionnaire was given to students in Malta, a zone of low-to-moderate seismic hazard where earthquake awareness is not culturally strong. The Maltese islands have, however, been affected historically by a number of earthquakes, the epicentres of which were in Eastern Sicily, the Sicilian Channel or as far away as the Hellenic arc. Some of these earthquakes produced considerable damage. In this way, the knowledge effectively possessed (relating to age, experience and area of origin), and the analogous and differing perceptions of earthquakes in different areas are highlighted. The data collected will be used to project and create new informative instruments through which students will become "geographic information volunteers", studying natural risks such as earthquakes and augmenting the territory's level of resilience. Consequently, local institutions will be able to refer to information about individuals' perception of seismic phenomena and use it to realise effective environmental planning and an efficient strategy of prevention., peer-reviewed

The Central Mediterranean is a region of active tectonics characterised by the interaction of a number of varied and sometimes poorly understood processes. Superimposed on the convergent scenario of the African plate pushing northwestward, a NE-SW directed extensional regime is active in the Sicily Channel, expressed in the form of a seismically active east-west trending system of strike-slip lineaments and a series of pull-apart grabens. The offshore seismicity of the Sicily channel, generally limited to magnitudes below 4.5, is normally difficult to quantify precisely, due to poor station coverage, yet it is believed that its analysis will considerably improve our understanding of the processes affecting the region. We present recent improvements to real and virtual seismic networking in the Central Mediterranean, based at the Seismic Monitoring and Research Unit (SMRU), University of Malta. Within the project SIMIT (B1-2.19/11) funded by the Italia-Malta Operational Programme 2007-2013, earthquake monitoring on the Maltese Islands is being upgraded through the installation of a further two broadband stations, one of which will be on the smaller island of Gozo. A new network, ML (Malta Seismic Network), has been internationally registered with the FDSN. At the same time, the installation and implementation of SeisComP3 has enabled the setting up of a virtual, real-time Central Mediterranean network, made up of 18 stations in Southern Italy (including Sicily, Lampedusa and Pantelleria) belonging to the Istituto Nazionale di Geofisica e Vulcanologia, 3 stations in Tunisia (National Institute of Meteorology of Tunisia) and the 3 stations on the Maltese Islands. This will allow us to rapidly perform more accurate hypocentral locations in the region. The virtual network, which also incorporates a number of more distant stations, has been tuned to issue SMS alerts for potentially felt events in the Sicily Channel detected by the network, and for strong earthquakes elsewhere. Within the SIMIT project, the alert system will include Civil Protection departments in Malta and Sicily. Small magnitude earthquakes, especially those located to the south and south-east of the Maltese Islands, may still go undetected by the network. In this case, use is made of a single-station polarization analysis method (LESSLA) developed at SMRU. The integration of data from the above methods allows us to produce a more comprehensive seismicity map for the Sicily Channel, which will be interpreted in terms of the dynamics of the Sicily Channel Rift System., peer-reviewed

The aim of this work is to study some particular geological sequences on the Maltese islands and in the city of Catania (Southern Italy). Geologically the two sites are quite different but several measurement points in both localities are characterised by sequences that represent a significant shear wave velocity inversion. The Maltese is- lands in the Central Mediterranean are composed of a simple 4-layer sedimentary sequence of Oligocene–Miocene limestones and clays. In particular, limestones overlying a clayey formation represent the shallower lithotypes that characterize the surficial geology in a large portion of the Maltese archipelago. On the contrary, the present geo- logic features of the Catania area are the result of tectonic uplift, sea level changes and lava flows originating from Etna eruptions. The area shows complex features with lateral heterogeneities at a local scale, due to the presence of volcanic and sedimentary units. In this study we make use of ambient noise recordings as well as moderate mag- nitude earthquakes in order to study the role of local geology on the site response in Catania. The recorded data were processed through standard and horizontal-to-vertical spectral ratios. Results of ambient noise and earthquake analysis, although showing significant differences in amplitude, are comparable in frequency. On the lava flows spectral ratios, significant amplification of the vertical component, that appear related to velocity inversion, were observed. Our findings appear linked to the complex wave-field generated by the lithologic heterogeneities existing in the area which seem to be related to alternating outcropping sediments and basaltic lavas. On the Maltese islands the main aim of this study was to identify any differences in site response, both in frequency and amplification, observed on different outcrops. All the investigated sites exhibit a clear and consistent peak in the frequency range of 1 Hz to 2 Hz. This is tentatively attributed to the presence of the buried clay formation layer everywhere below a variable thickness layer of limestone formation. The site effect induced by the clay layer has implications for the assessment of seismic risk, as well as for the validity of using Vs30 as a proxy for site class and site amplification., peer-reviewed

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International audience