Sebastiano D'Amico

Performance evaluation of Wied Dalam (WDD) seismic station in Malta

The continual operation of a permanent seismograph, now exceeding a couple of decades in some cases, naturally involves changes of hardware and soft- ware over time. Nonetheless, the long-term, consistent performance of the seismic station, and the good quality of its data, is very important for national seismic stud- ies investigating the local seismicity, and also important for the international seismological community research- ing regional tectonics and deep Earth structures. Here we investigate the data availability and quality of the currently only seismic station on Malta (WDD) since its installation in 1995, and establish spectral patterns in the seismic data that may be inuenced by diurnal vari- ations, seasonal weather changes, and/or site-specic settings. The results are important for the future de- ployment of permanent seismic stations on the Maltese islands, and for the analysis of local seismic hazard and ground motion studies.

Radial basis function neural networks to foresee aftershocks in seismic sequences related to large earthquakes

Radial Basis Function Neural Network are known in scientific literature for their abilities in function approximation. Above all, this particular kind of Artificial Neural Network is applied to time series forecasting in non-linear problems, where estimation of future samples starting from already detected quantities is very hardly. In this paper Radial Basis Function Neural Network was implemented in order to predict the trend of n(t) for aftershocks temporal series, that is the numerical series of daily-earthquakes number occurred after a great earthquake with magnitude M > 7.0 Richter. In particular we implemented the RBF-NN for the Colfiorito seismic sequence. The seismic sequences considered in this work are obtained following criteria already known in scientific literature [1], [2]. Results of proposed approach are very encouraging.

Ground-penetrating Radar Prospection at the Jesuits' Church in Valletta, Malta

In this paper, results of Ground-Penetrating Radar measurements performed at the church of the Jesuits in Valletta, Malta, are presented. This experimental activity was carried out during an International Training School on “Ground-Penetrating Radar for civil engineering and archaeology,” organized by COST Action TU1208 “Civil engineering applications of Ground-Penetrating Radar” and hosted by the University of Malta on January 25-29, 2016. The reported case study is of particular interest, as it shows that the well-known and commonly-adopted method of the diffraction hyperbolas, for the estimation of the propagation velocity from the measured radargrams, is not always reliable. As an alternative, a sequential migration with progressively lower trial propagation velocities was proposed and successfully used. Results presented in this paper include a series of B-Scans and depth slices. Several tombs were detected and located in the subsurface of the main nave of the church.

Heuristic advances in identifying aftershocks in seismic sequences

Soft computing techniques are known in scientific literature as capable methods for function approximation. Within this framework, they are applied to forecasting time series in non-linear problems, where estimation of the sample starting from actual measurements is very difficult. In this paper, we exploited soft computing techniques in order to predict the number of earthquakes (i.e. aftershocks) occuring after a large earthquake. The forecasting involves the aftershocks occuring day by day after a large earthquake, i.e. an earthquake having a magnitude M>=7.0 Richter. In particular, a comparison between radial basis function neural networks and support vector regression machines has been carried out, in order to overcome some problems related to the so called Delta/Sigma method, i.e. a probabilistic approach already used to detect aftershock events with magnitude M>5.5 after a large earthquake. A database for the Pacific area is used for the study, and the obtained results are very interesting.

Integrated GPR and passive seismic investigations at cultural heritage sites: Case studies in Malta

In this paper we report results from an integrated measurement campaign performed on the island of Malta. Both GPR and seismic noise data were gathered in two sites close to the sea, where two watchtowers built by the Order of St. John are located. The two investigations were performed on the top of the cliff inGolden Bay, close to the Ghajn Tuffieha Tower, and at the Madliena Tower in Pembroke. The main goal of the survey was to investigate the possible presence of natural or man-made elements that might affect the preservation of these monuments in the future. The investigations were therefore both on the two historical buildings and on a portion of soil nearby to also check the geological stability of the cliff since the towers are located right on its edge. The measurements were carried out with an innovative stepped frequency GPR system and with passive seismic instrumentation. In the following the main achievements will be presented.

Evaluation of seismic site response in the Maltese archipelago

The investigation of local ground conditions is an important part of seismic hazard assessment (Fäh et al., ). It is now well–established that earthquake ground shaking is not only a function of the earthquake magnitude and epicentral distance, but also of the site conditions, including soft layers in the sub–soil stratification and topographical features. Local geology can greatly alter the seismic waves from earthquakes by amplifying their amplitude, changing the frequency content and increasing the shaking duration during an earthquake (Kramer, ). In fact, several unconsolidated soft sites have suffered significantly greater damage than rock sites. One case was the  Michoacán earthquake which showed low peak ground acceleration near the epicenter, yet caused severe damage in Mexico City, which is found more than  km away and is characterized by soft shallow sediments (Campillo et al., ). The main parameters responsible for such effects are the shear– wave velocity (VS) structure and thickness of the sedimentary cover, the impedance contrast between the soft sediments and the underlying bedrock as well as the geometry of their interface (Parolai et al.,). Knowledge of the VS structure and/or the resonance frequency of soft soil layers is of utmost importance for the prevention or mitigation of earthquake disasters (Arai and Tokimatsu, ). Such information should contribute to earthquake–hazard mitiga-

Overview of the seismic hazard in the Sicily channel archipelagos

A joint Italo–Maltese research project (Costituzione di un Sistema Integrato di Protezione Civile Transfrontaliero Italo–Maltese, SIMIT) was financially supported by the European community. One of the aims of SIMIT was to improve the geological and geophysical information in Lampedusa and in Malta and ultimately to mitigate natural hazards. Although this region lies on the Sicily Channel Rift Zone, a seismically active domain of Central Mediterranean, the knowledge about seismotectonic and seismic hazard is not satisfactory. At present, seismic hazard assessment (SHA) for Italy (MPS Working Group, ), Tunisia (Ksentini and Romdhane, ) and more generally for whole European areas (Giardini et al., ) do exist, whereas no specific SHA for the Sicily channel archipelagos are available. The Sicily Channel appears to be a region of moderate seismic activity, with the seismicity mainly located in the surrounding areas (Fig. ). For the Malta archipelago a first catalogue, listing historical and felt earthquakes, was made by Galea (), whereas the Database Macrosismico Italiano (DBMI; Locati et al., ) does not list any data as regards earthquakes felt in Lampedusa. For this reason, in the present study, a theoretical seismic history was derived (Fig. ) for Lampedusa and Malta, using the European–Mediterranean Earthquake Catalogue (EMEC) (Grünthal and Wahlström, ) and the attenuation relationship for macroseismic intensity data by Pasolini et al. (). The two study areas do not appear to have been affected by strong earthquakes occurring in the Sicily channel, but they were somehow struck by major earthquakes occurring in the surrounding area. Although the present description seems to exclude large shaking effects, SHA for the study region is

The University of Malta (Seismic Monitoring and Research Unit), University of Basilicata and Imaa-CNR (Italy) operations during the 2012 Emilia seismic sequence

On 20th May 2012 (02:03 UTC), and on 29th May 2012 (07.00 UTC) two major earthquakes occurred in Northern Italy. The two earthquakes caused 27 people to be killed (7 on 20th May and 20 on 29th May), at least 400 injured, and up to 45, 000 homeless in total, with initial estimates placing the total economic loss at several billion Euros. The main goal of this communication is to describe the operations and efforts of several researchers and Institutions during the seismic crises of the Emilia sequence. The acquired data can provide tools to reduce the impact of future earthquakes on the local communities.