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Seismic anisotropy indicates organized melt beneath the Mid-Atlantic Ridge aids seafloor spreading

Sun, 01 Jan 2023 00:00:00 GMT

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.

Time-dependent horizontal-to-vertical spectral ratio (HVSR) analysis of ambient seismic noise

Thu, 01 Jan 2026 00:00:00 GMT

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.)

Thermal effluent exposure reveals early physiological constraints and the bioindicator potential of the invasive pearl oyster Pinctada radiata in a warming Mediterranean Sea

Thu, 01 Jan 2026 00:00:00 GMT

Title: Thermal effluent exposure reveals early physiological constraints and the bioindicator potential of the invasive pearl oyster Pinctada radiata in a warming Mediterranean Sea Authors: Marrone, Alessio; Geremia, Eugenio; Muscari Tomajoli, Maria Teresa; Esposito Marroccella, Sara; Petito, Adriana; Fasciolo, Gianluca; Donnarumma, Luigia; Venditti, Paola; Deidun, Alan; Napolitano, Gaetana Abstract: Thermal pollution from coastal power stations creates persistent local hotspots that can serve as in situ analogues of future ocean warming scenarios. We investigated the physiological and metabolic responses of the invasive pearl oyster Pinctada radiata (Leach, 1814) along a thermal gradient (26.3 °C, 27.1 °C, 28.5 °C) generated by the Delimara Power Station (Malta) cooling-water effluent. Redox-related biomarkers (reactive oxygen species [ROS] content; lipid hydroperoxides [HPs] and protein carbonyls [CO]; susceptibility to oxidants [ΔHPs]; total antioxidant capacity [TAC]; glutathione peroxidase [GPX] and glutathione reductase [GR] activity) and aerobic (cytochrome c oxidase [COX] activity) and anaerobic (lactate dehydrogenase [LDH] activity) metabolism were evaluated in gills and adductor muscles.; Gills exhibited no significant differences at 27.1 °C as compared to 26.3 °C. At 28.5 °C, reduced TAC, GPX, and GR, and increased HPs were indicative of oxidative damage. The adductor muscle exhibited a temperature-dependent response: at 27.1 °C, increased TAC, GPX, and GR, and reduced ΔHPs and CO, compared to 26.3 °C, were indicative of improved protection against oxidative damage; at 28.5 °C, the antioxidant profile was comparable to that at 26.3 °C. Interestingly, the increased ΔHPs and reduced TAC and GPX at 28.5 °C compared to 27.1 °C suggested a constraint of compensatory antioxidant mechanisms under higher thermal load. Metabolic analyses revealed unchanged COX activity in gills but reduced COX activity in the adductor muscle together with decreased LDH activity in both tissues, suggesting coordinated metabolic downregulation under prolonged thermal exposure. In conclusion, P. radiata exhibited thermal tolerance, although compensatory mechanisms became progressively constrained at the highest temperature. Further warming may therefore impair performance or shift distribution toward higher latitudes or deeper waters.

The diverse morphology of pockmarks around Aotearoa New Zealand

Sun, 01 Jan 2023 00:00:00 GMT

Title: The diverse morphology of pockmarks around Aotearoa New Zealand Authors: Hillman, Jess I. T.; Watson, Sally Joan; Maier, Katherine Leigh; Hoffmann, Jasper Justus Lutz; Bland, Kyle J.; Warnke, Fynn; Pecher, Ingo A.; Gorman, Andrew Robert; Davy, Bryan; Bull, Suzanne; Woelz, Susi Abstract: Seafloor pockmarks are abundant around Aotearoa New Zealand, occurring across a diverse range of tectonic, sedimentological and geomorphological settings. Globally, the formation and source of pockmarks is widely researched because they: 1) have potential links to subsurface hydrocarbon systems, 2) can provide important habitats for benthic organisms and 3) may be indications of fluid escape pathways or areas of sediment disturbance, which influence seafloor stability and could pose a risk to infrastructure. Pockmarks are widely associated with fluid release (such as gas or water) from subsurface reservoirs. However, the formation of pockmarks, the processes that shape and modify their morphology over time, and the relative timing of these events, remains enigmatic. Here, we compile the first national database of over 30,000 pockmarks around Aotearoa New Zealand, allowing us to begin to comprehend the dynamic processes that shape and affect pockmarks by exploring regional and inter-regional patterns in pockmark geometry and seabed characteristics. This compilation reveals several significant trends, including a distinct lack of correlation between active seafloor seeps and pockmarks, and a strong association of pockmarks with mud-rich seafloor substrate. Furthermore, we highlight key knowledge gaps that require further investigation moving forward, including a lack of constraint on the timing of pockmark formation, and limited modelling of the processes involved in their formation.