Seismic site response of unstable steep slope using noise measurements : the case study of Xemxija Bay area, Malta

Landslide phenomena involve the northern coast of Malta, affecting in particular the urban area of Xemxija. Limestones overlying a clayey formation represent the shallower lithotypes that characterize the surficial geology of this area, where lateral spreading phenomena and rockfalls take place. Ambient noise records, processed through spectral ratio techniques, were analysed in order to characterize the dynamic behavior of the rock masses affected by the presence of fractures linked to the landslide body existing in the area. Experimental spectral ratios were also calculated after rotating the horizontal components of the seismic signal, and a direct estimate of the polarization angle was also performed in order to investigate the existence of directional effects in the ground motion. The results of the morphologic survey confirmed the existence of large cliff-parallel fractures that cause cliff-edge and unstable boulder collapses. Such phenomena appear connected to the presence, inside the clay formation, of a sliding surface that was identified through the interpretation of the noise measurement data. The boundaries of the landslide area appear quite well defined by the pronounced polarization effects, trending in the northeastern direction, observed in the fractured zone and in the landslide body in particular.peer-reviewe

Seismic site response in Lampedusa

In the frame of a joint Italo–Maltese research project (Costituzione di un Sistema Integrato di Protezione Civile Transfrontaliero Italo– Maltese, SIMIT), financially supported by the European Community, a research plan was developed. Its final purpose is to mitigate natural hazards and to improve the geological and geophysical information in the area between the south–eastern Sicilian coast and the islands of Lampedusa and Malta. Although this region lies on the Sicily channel rift zone, a seismically active domain of the Central Mediterranean, knowledge about seismotectonic, seismic hazard and local seismic response is at present quite poor. In order to improve the awareness of problems linked to natural hazards and with the aim of toning down them, we investigated the island of Lampedusa (Pelagian archipelago). A multidisciplinary approach concerning tectonic, structural, morphologic and lithologic analyses was performed trying to contribute to fill up the information gap on the seismic features of this territory. The results of the geological–structural surveys were used to standardize the evaluation of the seismic hazard and, in particular, to understand the local seismic response of the distinct outcropping terrains and its influence on the dynamic behavior of existing buildings.peer-reviewe

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, 2004), Tunisia (Ksentini and Romdhane, 2014) and more generally for whole European areas (Giardini et al., 2013) 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. 1). For the Malta archipelago a first catalogue, listing historical and felt earthquakes, was made by Galea (2007), whereas the Database Macrosismico Italiano (DBMI11; Locatiet al., 2011) 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. 2) for Lampedusa and Malta, using the European–Mediterranean Earthquake Catalogue (EMEC) (Grünthal and Wahlström, 2012) and the attenuation relationship for macroseismic intensity data by Pasolini et al. (2008). 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.peer-reviewe

Seismic site response in Siracusa

In the frame of the Italo–Maltese research project (Costituzione di un Sistema Integrato di Protezione Civile Transfrontaliero Italo–Maltese, SIMIT), researches financially supported by the European Community were performed in the area between the south–eastern Sicilian coast and the islands of Lampedusa and Malta. Aim of these stud- ies is to mitigate natural hazards and to develop the geological and geophysical information in the investigated region. The damage to buildings further to a seismic input is tightly linked, besides their vulnerability, to both the characteristics of the maximum acceleration and frequency of the ground motion, as well as to the features of surface geology. From this point of view, the geophysical and geotechnical characterization of the soil conditions, down to the bedrock, is very important in order to identify the site effects, in terms of fundamental frequencies, for a correct planning of earthquake resistant structures.peer-reviewe

The role of slope instability on directional site effects observed at Fekruna Bay, Malta

The Maltese Archipelago is situated in the Mediterranean Sea, about 290 km NE of Tunisia and 90 km South of Sicily. It consists of three major islands: Malta and Gozo, the southerly and northerly islands respectively, and Comino which lies in the Comino straits separating the two largest islands. In order to better preserve the historical heritage, landscapes, and coastal areas and to promote tourism activities it has been proposed that the archipelago might be considered as an open air laboratory. In this context multidisciplinary studies integrating geology, geotechnical earthquake engineering, geomorphology as well as history and archeology were undertaken in order to develop and test methodologies for the assessment of the relationship between physical environment and cultural heritage (e.g., Soldati et al., 2008). The paper focuses on an integrated study about geomorphology and seismic site response in the Fekruna bay, in the area of Xemxija (northen-eastern part of the Malta Island, Fig. 1).N/

Dynamic properties of buildings evaluated through ambient noise measurements

It is well known that the damage level and its distribution during an earthquake is due to the combined effects of seismic hazard in the investigated area, the features of the local site response, based on the near–surface and subsurface ground conditions, as well as on the dynamic features of the erected buildings. The extent of building dam- age and its distribution is indeed tightly linked to the combined effect of local site response and the dynamic features of the human-made structures. The dynamic properties of a building are usually described through its natural frequency (or period T) and the damping ratio (ζ ), the latter representing the energy loss of an oscillating system. The damping ratio is important in seismic design since it allows to evaluate the ability of a structure to dissipate the vibration energy during an earthquake. Such energy causes a structure to have the highest amplitude of response at its fundamental period, which depends on the structure’s mass and stiffness. The knowledge of damping level and fundamental period of the building is therefore particularly important for estimating the seismic base shear force F in designing earthquake resistant structures.peer-reviewe

Shear wave velocity inversion and its influence on seismic site response : case studies from Malta and Catania (Italy)

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-reviewe

Influence of short-term storage on electrophoretic profile of bovine serum proteins

Storage represents a basic step of the pre-analytical phase for the accuracy of screening tests both in human and veterinary diagnostic laboratories. This study aimed to evaluate the effect of short-term storage on electrophoretic profile of serum proteins in dairy cows. Blood was collected from 18 clinically healthy cows and serum was divided into four aliquots. The first aliquot was immediately analysed (time 0). The second and the third aliquots were stored at +4°C for 24 and 48 h, respectively. The fourth aliquot was frozen at −20° C for 48 hours. A statistical analysis was performed on the obtained data. Albumin and α-globulins relative concentration and A/G ratio showed significant changes after 48 h storage. The results obtained in the current study showed that short-term storage influenced electrophoretic pattern of bovine serum proteins and the A/G ratio. Therefore, the refrigeration of bovine sera for 24 h at the most should be suggested to practitioners in order to obtain reliable serum protein..

Geophysical measurements for site response investigation : preliminary results on the island of Malta

The main goal of this study is to investigate the dynamic properties of main lithotypes outcropping on the island of Malta and to evaluate the general features of the local seismic response through the combined use of geophysical methods based on Rayleigh waves and horizontal to vertical noise spectral ratios. These kind of studies have unfortunately never been undertaken in Malta and, therefore, no shear wave velocity values and fundamental frequency of outcropping lithotypes have been published. The proposed preliminary results represent a valid set of data useful for evaluating seismic hazard and risk for the Maltese islands. Even if the seismic activity around the archipelago is generally of low to moderate magnitude the islands in the past were struck by large events in Sicily and the Hellenic arc resulting in considerable damage.peer-reviewe

Site effects on fault-zone : results from ambient noise measurements

It is well known that fault zones are generally characterized by a highly fractured low-velocity belt (damage zone), hundreds of meter wide, bounded by higher-velocity area (host rock) that can broaden for some kilometres (Ben-Zion et al,. 2003; Ben-Zion and Sammis, 2003, 2009 and references therein). Such geometrical setting and impedance contrast is in principle proficient to produce local amplification of ground motion (Peng and Ben-Zion, 2006; Calderoni et al., 2010; Cultrera et al., 2003; Seeber et al., 2000), as well as to support the development of fault zone trapped waves. There is a large number of papers that describe propagation properties of fault-guided waves (e.g., Li et al., 1994; Mizuno, Nishigami, 2006) in terms of ground motion amplification having a propensity to be maximum along the fault-parallel direction. These observations, both in theoretical and experimental approaches deal with almost pure strike slip faults such as the S. Andreas and the Anatolian faults (see Li et al., 2000; Ben Zion et al., 2003). Studies about local seismic response nearby fault zones have been performed in Italy and in California by Cultrera et al. (2003), Calderoni et al. (2010), Pischiutta et al. (2012) who observed evidences of ground motion amplification in the fault zone environments and strong directional effects with high angle to the fault strike. Similar studies, performed by Rigano et al. (2008) and Di Giulio et al. (2009) documented the presence of a systematic polarization of horizontal ground motion, near faults located on the eastern part of the Etnean area, that was never coincident with the strike of the tectonic structures. These directional effects were observed both during local and regional earthquakes, as well as using ambient noise measurements, therefore suggesting the use of microtremors for investigating ground motion polarization properties along and across the main tectonic structures of all the volcanic area. All the observations showed evidence of directional amplifications not parallel to the fault strike, as would have been expected for trapped waves. In the present study, the results of new measurements are shown and discussed. The data were recorded in newly investigated tectonic structures of the volcano located both on the western flank of Mt. Etna (Ragalna fault system) and on the eastern flank of the volcano (Piedimonte fault) as well as in a non-volcanic area (Malta Island), located in the Hyblean foreland. Moreover, several measurements were performed in areas significantly distant from the studied tectonic structures (Piano dei Grilli and Malta area), in order to observe how directional effects can change at increasing distance from the fault lines.peer-reviewe