https://www.um.edu.mt/library/oar/handle/123456789/403 2026-08-25T10:56:13Z https://www.um.edu.mt/library/oar/handle/123456789/148652 Title: Seismic anisotropy indicates organized melt beneath the Mid-Atlantic Ridge aids seafloor spreading Authors: Kendall, J. M.; Schlaphorst, D.; Rychert, C. A.; Harmon, N.; Agius, Matthew; Tharimena, S. Abstract: Lithospheric plates diverge at mid-ocean ridges and asthenospheric mantle material rises in response. The rising material decompresses, which can result in partial melting, potentially impacting the driving forces of the system. Yet the geometry and spatial distribution of the melt as it migrates to the ridge axis are debated. Organized melt fabrics can cause strong seismic anisotropy, which can be diagnostic of melt, although this is typically not found at ridges. We present anisotropic constraints from an array of 39 ocean-bottom seismometers deployed on 0–80 Ma lithosphere from March 2016 to March 2017 near the equatorial Mid- Atlantic Ridge (MAR). Local and SKS measurements show anisotropic fast directions away from the ridge axis, which are consistent with strain and associated fabric caused by plate motions with short delay times, δt (<1.1 s). Near the ridge axis, we find several ridge-parallel fast splitting directions, φ, with SKS δt that are much longer (1.7–3.8 s). This is best explained by ridge-parallel sub-vertical orientations of sheet-like melt pockets. This observation is much different than anisotropic patterns observed at other ridges, which typically reflect fabric related to plate motions. One possibility is that thicker sub-ridge lithosphere with steep subridge topography beneath slower spreading centers focuses melt into vertical, ridge-parallel melt bands, which effectively weakens the plate. Associated buoyancy forces elevate the subridge plate, providing greater potential energy and enhancing the driving forces of the plates. 2023-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/148598 Title: Deterministic quantum computation with one-clean-qubit model as an open quantum system Authors: Xuereb, Jake; Campbell, Steve; Goold, John; Xuereb, Andre Abstract: The deterministic quantum computation with one-clean-qubit model (DQC1) complexity class, or power-ofone qubit model, is examined as an open quantum system.We study the dynamics of a register of qubits carrying out a DQC1 algorithm and show that, for any algorithm in the complexity class, the evolution of the logical qubit can be described as an open quantum system undergoing a dynamics which is unital. Unital quantum channels respect the Tasaki-Crooks fluctuation theorem, and we demonstrate how this is captured by the thermodynamics of the logical qubit. As an application, we investigate the equilibrium and nonequilibrium thermodynamics of the DQC1 trace estimation algorithm. We show that different computational inputs, i.e., different traces being estimated, lead to different energetic exchanges across the register of qubits and that the temperature of the logical qubit impacts the magnitude of fluctuations experienced and quality of the algorithm. 2023-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/148524 Title: Time-dependent horizontal-to-vertical spectral ratio (HVSR) analysis of ambient seismic noise Abstract: Existing local research has employed the horizontal-to-vertical spectral ratio (HVSR) for static microzonation and long-term groundwater monitoring. Building on this work, this thesis provides the first high-resolution quantification of how sub-daily meteorological fluctuations, specifically wind-driven noise and atmospheric variables, directly modulate seismic site response parameters across the stations of the Malta Seismic Network in the Maltese archipelago. By establishing these correlations, this study enhances the methodological accuracy of HVSR in the Maltese context, providing a framework to isolate meteorological noise from geological signals and enabling more reliable site response assessments for local engineering and microzonation projects. This study analyses four years (2017-2020) of continuous seismic data recorded by the Malta Seismic Network to investigate temporal variability in HVSR parameters. The research evaluates how HVSR peak frequency and amplitude evolve and examines the potential influence of meteorological variables, including wind speed, precipitation, temperature, and relative humidity. Statistical analysis is used to identify stations that exhibit sensitivity to environmental forcing and to assess the extent to which such factors may influence the stability and interpretation of HVSR measurements in the Maltese Islands. Forward modelling was also used to confirm whether the observed meteorological effects can potentially create subsurface parameter changes, such as variations in soil moisture or density, which could affect the HVSR measurements. This thesis further confirms that HVSR parameters are sensitive to wind strength and reveals that two stations (MELT and CBH9) have a heightened sensitivity to wind speed compared to other stations within the Malta Seismic Network. Hence, caution should be exercised when analysing data from these stations during windy days. Association between HVSR and other meteorological parameters, including precipitation, revealed weak effect sizes, indicating that other short-term meteorological forcing is not registered by HVSR. Description: B.Sc. (Hons)(Melit.) 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/148517 Title: The variability of Heteracris adspersa (Redtenbacher, 1889) re-examined (Orthoptera : Acrididae, Eyprepocnemidinae) Authors: Cassar, Louis F.; Lanfranco, Sandro; Massa, Bruno Abstract: A new subspecies of Heteracris adspersa was described in 1978 on the basis of morphometrics and structure configuration of the male subgenital plate from specimens collected in Sardinia. The present study examines specimens (n=175) from a broad suite of localities, ranging from the Middle East across to the western Mediterranean. Statistical analyses are subsequently carried out on a revised dataset comprising 94♂♂ and 55♀♀. Microscopic examination of the subgenital plate is also conducted on specimens from Sardinia, Sicily, Malta and Yemen and compared with those published in the original description. Findings demonstrate that the subspecies massai is practically an artefact of unintended consequence, essentially a case of taxonomic inflation, in view of evident intra and interpopulation variability across a wide geographic area; consequently, H. a. massai is synonymised. 2026-01-01T00:00:00Z