https://www.um.edu.mt/library/oar/handle/123456789/36020 Thu, 09 Apr 2026 20:29:29 GMT 2026-04-09T20:29:29Z https://www.um.edu.mt/library/oar/handle/123456789/73648 Title: Seismic input modelling for relevant earthquakes in eastern Sicily Abstract: Assessment of potential ground motions in seismically active regions is essential for purposes of seismic design and analysis. One key challenge in modern day engineering practices is to better understand the processes associated with ground shaking in order to mitigate the effects and to cope with future earthquakes. In recent years, ground motion simulations are becoming the most effective tool to study characteristics of the faulting mechanisms and regional seismic parameters. The fundamental approach in ground motion simulations is to mimic the source mechanisms, regional wave propagation properties and site conditions for estimating reliable synthetic records. A simulation technique, widely used in recent years, is based on the finite-fault stochastic method (EXSIM, Motazedian and Atkinson, 2005; Boore, 2009). It requires the specification of parameters describing source, path and site characteristics, into simple functional forms. These parameters are crucial for successful ground motion simulations, since the damage caused by earthquakes depends strictly on them. The main goal of this thesis is to understand the key parameters that locally control the ground motion, as well as to investigate the relative contributions of local site effects. The thesis includes two main parts. The first one is dedicated to the investigation of the site effects in the Etnean area and in the Hyblean Plateau. Seismic waves are greatly modified by the local geology and soil conditions. Since geometry and soil conditions of the sedimentary layer often vary over short distances, nature and levels of ground shaking can vary significantly within a small area. Records of both earthquakes and ambient noise, taken from the stations of the Permanent Seismic Network (RSP) of Eastern Sicily (INGV-Osservatorio Etneo, Catania) were analysed in detail and processed through spectral ratio techniques (Horizontal to Vertical Fourier spectral ratios; Horizontal to Vertical Response Spectra ratio) in order to compute the corresponding amplification functions and a new soil classification scheme. In particular, the soil classification was based on the estimation of the dominating period of site response. Two approaches were used, taking into account either the Fourier or the response spectra. The first approach is an indirect measurement of the local amplification since it calculates the average horizontal-to-vertical spectral ratios comparing them to the theoretical curves coming from literature information about the structure under every site. Then, amplification functions were computed and later grouped, thus finding an average amplification function for each class. The second approach performs a more direct estimate of site effects computing response spectral ratio of each station with respect to the response spectrum of a reference station, hence directly obtaining the transfer functions, that were then subdivided into groups. The 7 implemented classification scheme is similar to the one proposed by Zhao et al. (2006). In both methods, four classes were identified. The main objective of the second part is to validate the soil classification scheme with the corresponding amplification functions. Two real events, which were localized respectively at lower and higher depth beneath the Etna volcano, were simulated, using the obtained amplification functions and considering the seismological parameters regarding the source and the path reported in the literature. Simulated ground motion parameters and recorded data were finally compared. The obtained results prove the validity of the obtained site amplification functions, which can be used by scientific community as input to simulate ground motion for the studied areas (EXSIM program). They also demonstrate the validity of the proposed soil classification scheme. In the Etnean area, since it is characterized by alternating soft and rigid terrains, it is necessary to use a method that considers all the stratigraphic succession overlying the bedrock and thus different from the conventional VS30. Indeed, it is widely shown that a classification scheme of the main soil categories, founded on the average shear wave velocity of the upper 30 m alone, is not sufficient to categorise the seismic responses of geologically complex areas. Description: PH.D. Sun, 01 Jan 2017 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/73648 2017-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/73632 Title: Geophysical investigations for modelling of earthquake ground shaking in the Maltese islands Abstract: The Maltese islands have suffered damage from earthquakes in the historical past. Over the last few decades, the building density has increased dramatically, with building heights of more than five storeys becoming increasingly common. The urban development has even spilled out on to geologically more vulnerable areas. To date, no building codes are officially in force in the Maltese islands, and the National Annex for the EC8 guidelines is still in the process of being drafted. This study investigates the ground response of the islands to potential earthquake shaking, in particular on those areas characterised by a layer of clays and marls (up to 75m thick in places) embedded in the stratigraphy. The velocity inversion introduced by this layer makes the average shear-wave velocity in the uppermost 30 m (VS30), not always suitable for seismic microzonation purposes. Such a layer may still produce amplification effects, however would not contribute to the numerical mean of shearwave velocity (VS) in the upper 30 m. For this purpose, and for investigating possible local site effects over the islands, the first investigation was the establishment of shear-wave velocity profiles with a focus on areas characterised by a buried layer of clay. This was carried out through the inversion of surface wave dispersion data, using multi-station Extended Spatial Auto-Correlation (ESAC) together with single-station Horizontal-to-Vertical Spectral Ratio (H/V). Geophone arrays were set up in an L-shaped configuration at 27 sites and the effective Rayleigh wave dispersion curves extracted. At all sites characterised by the buried clay layer, the dispersion curve exhibited a normal dispersive trend at low frequencies, followed by an inverse dispersive trend at high frequencies. This lithological sequence also gave rise to a clear H/V peak that was observed consistently at all such sites in a narrow frequency range between 1 and 2 Hz. From the joint inversion procedure, the VS in the Blue Clay was found to vary between 350 and 580 m s−1, generally depending on the overburden thickness. A considerable variation in the VS within the Upper Coralline Limestone was also observed; related to the geological variety of regional facies within this formation, ranging from highly fractured (VS = 550 m s−1) to very competent (VS = 1100 m s−1). The spectral response to earthquake shaking of a surface sedimentary layer package with a measured VS profile was modelled through the equivalent linear programme SHAKE2000. The input earthquake time series was obtained from an appropriate selection of real seismograms, conformant with the local seismic hazard. Maps of amplification factors and 5% damped elastic response spectra confirm that the clay, even when buried under a hard outcropping layer can still produce significant amplifications at frequencies which are of engineering interest. As expected, sites where the clay outcrops, or lies at shallow depth below the surface, are particularly vulnerable. The amplification potential of the clay layer was also demonstrated directly through the Standard Spectral Ratio (SSR) method using a bedrock reference site. Description: PH.D. Sun, 01 Jan 2017 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/73632 2017-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/37155 Title: Development of an innovative integrated Maltese coastal map for navigational purposes Abstract: The main objective of this present study is to create a unique integrated map of the Gozitan coastline by combining all coastal features from several types of sources, from existing maps and from in-situ observations. Coastal population growth, urbanisation, marine pollution and the degradation in water quality have amplified the need for adequate research, management and monitoring protocols. Coastal mapping is a useful tool at displaying information in an understandable and accurate manner. Today, scientists and researchers make use of several geospatial tools, imagery and maps, to accurately present a wide range of data through several layers. The general public, stakeholders and managers can equally benefit from online geoinformatics services, such as Google Maps. In this project, the location of several coastal infrastructures along the coastline of Gozo, including ladders, slipways, restaurants, bars, parking areas, valleys and police stations to mention a few, are recorded, digitised and presented in an online and publicly available digital interactive map that is based on Google Maps API. Areas of interest like swimming zones are also delineated. It is important to mention that this is a phased approach as it can be broken down into a number of steps. Information pertaining to multiple users and related to characteristics of each coastal zone is presented. The interactive map, accessible through desktop and mobile devices can be accessed through the URL http://ioi.research.um.edu.mt/coastaldataneil/. The geo-referenced base of information collected in this study is intended to provide a baseline and support future management in the area of coastal mapping. Together with similar services, this prototype will enhance awareness and knowledge about the coastal zone and facilitate coastal navigation. Description: M.SC.APPLIED OCEANOGRAPHY Sun, 01 Jan 2017 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/37155 2017-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/37149 Title: A preliminary attempt at characterising beached material through aerial footage in the Maltese islands (central Mediterranean) Abstract: The study aims to elaborate a protocol based on the monitoring of Coastal Litter accumulation in the Maltese Islands while using a drone. Three locations are selected from the North East Marine Protected Area (NEMPA) situated in Malta: Qawra Point, the western side and the eastern side of Bahar ic-Caghaq. These areas are considered hotspots to check whether hydrodynamical conditions such as the wind parameters (wind speed, the average wind speed and the wind direction), measured with the anemometer, and the wave exposure index, calculated using the Thomas exposure index equation, are influencing the accumulation of litter along the coastlines. In addition, tourism or local activities are taken in consideration in order to check if they are determining this increase in marine and coastal pollution. Data is collected using a drone: this is an innovative way to acquire data through aerial footage. In fact, the drone has a capacity of approximately 30 minutes each battery, therefore each survey records items in large and not easily accessible area and in a short period of time. This thesis defines a new protocol which could be included in the achievement of a "Good Environment Status" of the Marine Strategy Framework Directive by 2020. In particular, the descriptor 10 of this Directive is based on Marine Litter, therefore the protocol could be used to implement the research on this nowadays important and urgent topic that must be recovered. In the next chapters, the defining of the protocol is explained and described (in the material and methods chapter), while results illustrate the recording of coastal litter and the statistical analyses done show which factor is influencing the accumulation of litter in the areas of study. Limitations of the protocol and further approaches are included in the study in order to be tackled in future projects based on aerial monitoring programme. Description: M.SC.APPLIED OCEANOGRAPHY Sun, 01 Jan 2017 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/37149 2017-01-01T00:00:00Z