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.peer-reviewe

Moment tensor solutions, high-frequency ground motion scaling and earthquake simulations in southern Italy

The evaluation of the expected peak ground motion caused by an earthquake is an important problem in earthquake seismology. It is particularly important for regions where strong-motion data are lacking. With the approach presented in this study of using data from small earthquakes, it is possible to extrapolate the peak motion parameters beyond the magnitude range of the weak-motion data set on which they are calculated. To provide a description of the high frequency attenuation and ground motion parameters in southern Italy we used seismic recordings coming from two different projects: the SAPTEX (Southern Apennines Tomography Experiment) and the CAT/SCAN (Calabria Apennine Tyrrhenian – Subduction Collision Accretion Network). We used about 10,000 records with magnitudes between M=2.5 and M=4.7. Using regression model with the large number of weak-motion data, the regional propagation and the absolute source scaling were determined. To properly calibrate the source scaling it was necessary to compute moment magnitudes of several events in the data set. We computed the moment tensor solutions using the “Cut And Paste” and the SLUMT methods. Both methods determine the source depth, moment magnitude and focal mechanisms using a grid search technique. The methods provide quality solutions in the area in a magnitude range (2.5-4.5) that has been too small to be included in the Italian national earthquake catalogues. The derived database of focal mechanisms allowed us to better detail the transitional area in the Messina Strait between the extensional domain related to subduction trench retreat (southern Calabria) and the compressional one associated with continental collision (central-western Sicily). Stochastic simulations are generated for finite-fault ruptures using the derived propagation parameters to predict the absolute peaks of the ground acceleration for several faults, magnitude, and distance range, as well as beyond the magnitude range of the weak-motion data set on which the input parameters are calculated. Finally we derived a functional form for a predictive relationship valid in the study 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/

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

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 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

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

Investigating the use of UAV systems for photogrammetric applications : a case study of Ramla Bay (Gozo, Malta)

In this study, we present the 3D digital model of Ramla Bay (Gozo) obtained by using photograms taken from drones. The high-resolution 3D model of Ramla Bay allowed the construction of a detailed Digital Elevation Model (DEM). Comparison of an earlier LIDAR data derived DEM (ERDF 156 Data, 2013) and the photogrammetric DEM developed in this study allowed to make preliminary observations regarding the potential evolution of the coastal area over the last 5 years. This study serves as a proof of concept to demonstrate that coastal evolution can be quantitatively analysed in terms of changes of the sand dune systems. Furthermore, the technique used in this paper represents a good compromise in terms of cost effectiveness and a valid substitute for laser scanner survey. It is also useful for monitoring the dynamics of the beach-dune system and the characterization of the coast for the mitigation of coastal erosion.peer-reviewe