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Determining reliable cable ampacities for marine High Voltage Cables is currently the subject of significant industry and academic reassessment in order to optimize (maximizing load while maintaining safe operating temperatures) design and reduce costs. Ampacity models can be elaborate, and inaccuracies are increasingly predicated on the uncertainty in environmental inputs. A stark example is the role of ambient temperature at cable depth, which, due to the scale of cables and the inaccessibility of the seafloor, is commonly estimated at 15 °C. Oceanographic models incorporating ocean bottom temperature are increasingly available, and they achieve coverage and spatiotemporal resolutions for cable applications without the requirement for project specific measurements. Here, a rudimental validation of the AMM15 and AMM7 mean monthly ocean bottom temperature models for the NW European Shelf indicates encouraging accuracies (MBE ≤ 1.48 °C; RMSE ≤ 2.2 °C). A series of cable case studies are used to demonstrate that cable ratings can change between −4.1% and +7.8% relative to ratings based on a common static (15 °C) ambient temperature value. Consideration of such variations can result in both significant ratings (and hence capital expenditure and operating costs) gains and/or the avoidance of cable overheating. Consequently, validated modelled ocean bottom temperatures are deemed sufficiently accurate, providing incomparable coverage and spatiotemporal resolutions of the whole annual temperature signal, thereby facilitating much more robust ambient temperatures and drastically improving ampacity estimates. [ABSTRACT FROM AUTHOR]

Heat flow measurements indicate hydrothermal activity in oceanic crust continues at least for 65 m.y. after formation. Hydrothermal activity progressively fills cracks and pores with alteration products, which is expected to lead to a trend of increasing seismic velocities with age. Compilations of seismic-P-wave velocity models inverted from ocean bottom seismometer (OBS) data have failed to detect such an aging trend beyond crustal ages of ca. 10 Ma. However, in these models, the velocities of the uppermost crust, where fluid flow would be most concentrated, are poorly resolved. This is because as the oceanic crust matures, the first crustal arrivals on OBS records (which best resolve upper crustal velocities using tomographic inversion), become hidden in the coda of the water wave. This may lead to the masking of any aging trend in the seismic velocities. For the first time, we show how including downward continuation (DC) in the analysis of OBS data collected across 65 Ma seafloor significantly improves measurements of the P-wave velocities of the upper crust. Our new analysis reveals a highly heterogeneous upper crust, with ridge-parallel P-wave velocity variations of 25%, implying local porosity values that are up to double that of global averages. Our new results, combined with other most recent advanced seismic analyses, reveal that seismic velocities indeed evolve with age up to at least 70 Ma, confirming that hydrothermal activity continues in mature oceanic crust. [ABSTRACT FROM AUTHOR]

Oceanic lithosphere carries volatiles, notably water, into the mantle through subduction at convergent plate boundaries. This subducted water exercises control on the production of magma, earthquakes, formation of continental crust and mineral resources. Identifying different potential fluid sources (sediments, crust and mantle lithosphere) and tracing fluids from their release to the surface has proved challenging1. Atlantic subduction zones are a valuable endmember when studying this deep water cycle because hydration in Atlantic lithosphere, produced by slow spreading, is expected to be highly non-uniform2. Here, as part of a multi-disciplinary project in the Lesser Antilles volcanic arc3, we studied boron trace element and isotopic fingerprints of melt inclusions. These reveal that serpentine—that is, hydrated mantle rather than crust or sediments—is a dominant supplier of subducted water to the central arc. This serpentine is most likely to reside in a set of major fracture zones subducted beneath the central arc over approximately the past ten million years. The current dehydration of these fracture zones coincides with the current locations of the highest rates of earthquakes and prominent low shear velocities, whereas the preceding history of dehydration is consistent with the locations of higher volcanic productivity and thicker arc crust. These combined geochemical and geophysical data indicate that the structure and hydration of the subducted plate are directly connected to the evolution of the arc and its associated seismic and volcanic hazards. Serpentine subducted below the Lesser Antilles volcanic arc supplies water to the arc, controlling the location of seismicity, volcanic productivity and thickness of crust. [ABSTRACT FROM AUTHOR]

Estimating the location of geologic and tectonic features on a subducting plate is important for interpreting their spatial relationships with other observables including seismicity, seismic velocity and attenuation anomalies, and the location of ore deposits and arc volcanism in the over-riding plate. Here we present two methods for estimating the location of predictable features such as seamounts, ridges and fracture zones on the slab. One uses kinematic reconstructions of plate motions, and the other uses multidimensional scaling to flatten the slab onto the surface of the Earth. We demonstrate the methods using synthetic examples and also using the test case of fracture zones entering the Lesser Antilles subduction zone. The two methods produce results that are in good agreement with each other in both the synthetic and real examples. In the Lesser Antilles, the subducted fracture zones trend northwards of the surface projections. The two methods begin to diverge in regions where the multidimensional scaling method has its greatest likely error. Wider application of these methods may help to establish spatial correlations globally. [ABSTRACT FROM AUTHOR]

The Sumatran subduction zone exhibits strong seismic and tsunamogenic potential with the prominent examples of the 2004, 2005 and 2007 earthquakes. Here, we invert travel-time data of local earthquakes for vp and vp=vs velocity models of the central Sumatran forearc. Data were acquired by an amphibious seismometer network consisting of 52 land stations and 10 ocean-bottom seismometers located on a segment of the Sumatran subduction zone that had not ruptured in a great earthquake since 1797 but witnessed recent ruptures to the north in 2005 (Nias earthquake, Mw D 8:7) and to the south in 2007 (Bengkulu earthquake, Mw D 8:5). The 2-D and 3-D vp velocity anomalies reveal the downgoing slab and the sedimentary basins. Although the seismicity pattern in the study area appears to be strongly influenced by the obliquely subducting Investigator Fracture Zone to at least 200 km depth, the 3-D velocity model shows prevailing trench-parallel structures at depths of the plate interface. The tomographic model suggests a thinned crust below the basin east of the forearc islands (Nias, Pulau Batu, Siberut) at ~180 km distance to the trench. vp velocities beneath the magmatic arc and the Sumatran fault zone (SFZ) are around 5 km s-1 at 10 km depth and the vp=vs ratios in the uppermost 10 km are low, indicating the presence of felsic lithologies typical for continental crust. We find moderately elevated vp=vs values of 1.85 at ~150 km distance to the trench in the region of the Mentawai Fault. vp=vs ratios suggest an absence of large-scale alteration of the mantle wedge and might explain why the seismogenic plate interface (observed as a locked zone from geodetic data) extends below the continental forearc Moho in Sumatra. Reduced vp velocities beneath the forearc basin covering the region between the Mentawai Islands and the Sumatra mainland possibly reflect a reduced thickness of the overriding crust. [ABSTRACT FROM AUTHOR]

The Sumatran subduction zone exhibits strong seismic and tsunamogenic potential with the prominent examples of the 2004, 2005 and 2007 earthquakes. Here, we invert travel time data of local earthquakes for vp and vp/vs velocity models of the central Sumatran forearc. Data were acquired by an amphibious seismometer network consisting of 52 land stations and 10 ocean bottom seismometers located on a segment of the Sumatran subduction zone that had not ruptured in a great earthquake since 1797 but witnessed recent ruptures to the north in 2005 (Nias earthquake, Mw=8.7) and to the south in 2007 (Bengkulu earthquake, Mw=8.5). 2D and 3D vp velocity anomalies reveal the downgoing slab and the sedimentary basins. Although the seismicity pattern in the study area appears to be strongly influenced by the obliquely subducting Investigator Fracture Zone to at least 200 km depth, the 3D velocity model shows prevailing trench parallel structures at depths of the plate interface. The tomographic model suggests a thinned crust below the basin east of the forearc islands (Nias, Pulau Batu, Siberut) at ~ 180 km distance to the trench. Vp velocities beneath the magmatic arc and the Sumatran fault zone SFZ are around 5 km/s at 10 km depth and the vp/vs ratios in the uppermost 10 km are low, indicating the presence of felsic lithologies typical for continental crust. We find moderately elevated vp/vs values of 1.85 at ~ 150 km distance to the trench in the region of the Mentawai fault. Vp/vs ratios suggest absence of large scale alteration of the mantle wedge and might explain why the seismogenic plate interface (observed as a locked zone from geodetic data) extends below the continental forearc Moho in Sumatra. Reduced vp velocities beneath the forearc basin covering the region between Mentawai Islands and the Sumatra mainland possibly reflect a reduced thickness of the overriding crust. [ABSTRACT FROM AUTHOR]

In the North Atlantic Ocean, a mid-ocean ridge bisects the Icelandic mantle plume, and provides a window into its temporal evolution. V-shaped ridges of thick oceanic crust observed south of Iceland are thought to record pulses of upwelling within the plume. Specifically, excess crust is thought to form during the quasi-periodic generation of hot solitary waves triggered by thermal instabilities in the mantle. Here we use seismic reflection data to show that V-shaped ridges have formed over the past 55 million years-providing the longest record of plume periodicity of its kind. We find evidence for minor, but systematic, asymmetric formation of crust, due to migration of the mid-ocean ridge with respect to the underlying plume. We also find changes in periodicity: from 55 to 35 million years ago, the V-shaped ridges form every 3 million years or so and reflect small fluctuations in plume temperature of about 5-10 °C. From 35 million years ago, the periodicity changes to about 8 million years and reflects changes in mantle temperature of 25-30 °C. We suggest that this change in periodicity is probably caused by perturbations in the thermal state at the plume source, either at the mantle-transition zone or core-mantle boundary. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

Objective: Remote patient monitoring (RPM) beat-to-beat blood pressure (BP) provides an opportunity to measure poststroke BP variability (BPV), which is associated with clinical stroke outcomes. BP sampling interval (SI) influences ambulatory BPV, but RPM BP SI optimisation research is limited. SI and RPM device capabilities require compromises, meaning SI impact requires investigation. Therefore, this study assessed healthy and stroke subtype BPV via optimised BP sampling, aiding sudden BP change identification and potentially assisting cardiovascular event (recurrent stroke) prediction., Methods: Leicester Cerebral Haemodynamic Database ischaemic [acute ischaemic stroke (AIS), n = 68] and haemorrhagic stroke (intracerebral haemorrhage, n = 12) patient and healthy control (HC, n = 40) baseline BP data were analysed. Intrasubject and interpatient SD (SDi/SDp) represented individual/population variability with synthetically altered SIs. Matched-filter approaches using cross-correlation function detected sudden BP changes., Results: At SIs between 1 and 180 s, SBP and DBP SDi staticised while SDp increased at SI < 30 s. Mean BP and HR SDi and SDp increased at SI < 60s. AIS BPV, normalised to SI1s, increased at SI30s (26%-131%) and SI120s (1%-274%). BPV increased concomitantly with SI. Cross-correlation analysis showed HC and AIS BP sudden change detection accuracy reductions with increasing SI. Positive BP deviation detection fell 48.48% (SI10s) to 78.79% (SI75s) in HC and 67.5% (SI10s) to 100% (SI75s) in AIS. Negative BP deviation detection fell 50% (SI10s) to 82.35% (SI75s) in HC and 52.27% (SI10s) to 95.45% (SI75s) in AIS., Conclusion: Sudden BP change detection and BPV are relatively robust to SI increases within certain limits, but accuracy reductions generate unacceptable estimates, considerable within RPM device design. This research warrants further SI optimisation., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)