Large motion analysis of compliant structures using euler parameters

The large motions that a compliant offshore structure experiences were analysed using Euler parameters. Firstly, the equations of motion of a rigid body undergoing large translations and rotations were obtained using the Lagrangian formulation. Secondly, the hydrodynamic forces acting on the structure were calculated using the modified Morison's equation. A tension-leg platform (TLP) subjected to an oblique incident wave was then analysed using the above formulation. This was followed by an analysis of an articulated tower for comparison with the results of other researchers. An example showing the tower undergoing subharmonic oscillations was also included.     

Offshore pile foundations in sand under earthquake loading

A new approach to the analysis of pile foundations, developed recently for the analysis of a pile supported offshore structure, is described. The method uses a coupled soil-pile analysis which takes into account the non-linear resistance of the pile to lateral deformation and the effect of progressively increasing pore water pressures on that resistance. The analysis allows also for radiation of energy away from the site. Typical of results given in the paper are: (1) the effect of pore water pressure increases on the API cyclic loading curves, (2) the degradation in lateral stiffness due to pore pressure increases for piles with fixed and free heads, (3) variations in deflections and moments with depth due to pore water pressure from those predicted using current API procedures.     

A Synthetic Haematite Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Application to Iron Oxide‐Cu‐Au Systems

In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe₂O₃) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe₂O₃ were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology.     

Securing supply: governing drinking water in the Northern Territory

ABSTRACT

This article considers the spatial and material implications of drinking water regulation in the Northern Territory (NT) of Australia. Responding to water contamination and scarcity events in remote NT communities, we argue that the politico-bureaucratic edifice of uniform drinking water governance and service provision across the NT is a state-curated fiction. The article outlines the available legislative protections for drinking water supply in the NT, which include minimum quality standards, water allocation mechanisms, testing regimes, and so on. These are shown to vary significantly between geographic locations and we argue that this produces a racialised ‘archipelago’ of differentiated islands of drinking water governance (Bakker 2003. “Archipelagos and Networks: Urbanization and Water Privatization in the South.” The Geographical Journal 169 (4): 328–341). Using the Gulf country town of Borroloola as a case study, the article then examines the colonial and land rights bases of this spatial variegation, and its significance for drinking water infrastructure provision and remediation. In doing so, we consider how the entropic materialities of ageing infrastructures work to further confound effective drinking water regulations and their practical enactments. The article argues that it is crucial to understand the limits of drinking water regulation in the NT, in order to elucidate the racialised distribution of potential environmental harms, and to mitigate further toxic inheritances.     

1-D and 2-D analyses of weak motion data in Fraser Delta from 1966 Duvall earthquake

The 1996 Duvall earthquake in Washington State triggered ground motion stations in the Fraser Delta, British Columbia, located on varying depths of Holocene and Pleistocene soils to a maximum depth of 800 m and one station on bedrock. Recorded ground motions were used to examine the applicability of 1-D and 2-D site response analyses for amplification studies in the Delta. 1-D response analysis gave a good indication of the period of peak response. Response spectra computed by 1-D analysis did not compare well with recorded spectra except at very deep sites. The use of 2-D analyses to include buried topography generally improved the predictions of site response spectra at the shallow sites. However, for the shallow earth sites, the recorded motions showed a strong spectral response at short periods in the range of 0.1–0.25 s. Neither 1-D nor 2-D analysis predicted this response.     

Analysis of ground motions at Treasure Island site during the 1989 Loma Prieta earthquake

Site response analyses and coherence studies were conducted at the Treasure Island site where surface motions were recorded during the Loma Prieta earthquake. The analyses were conducted using a nonlinear dynamic effective stress method which took into account the effects of the liquefaction that occured at the site. The rock motions recorded at nearby Yerba Buena Island were used as input motions. Computed and recorded ground motions transverse to the direction of wave propagation and associated response spectra were in good agreement. Agreement was also good in the radial direction, except in certain frequency bands higher than 1·25 Hz. Coherence studies showed that some of these discrepancies may be due to low coherence between the Treasure Island and Yerba Buena motions in these same frequency bands.     

The Asosa region of western Ethiopia: a golden exploration opportunity

Gold mining has a legendary history in Ethiopia, with Ethiopian mines providing gold to the ancient Egyptian empire and possibly even King Solomon's Mines and the Queen of Sheba. Today, gold occurs in the Pan‐African age schist belt and Tertiary basaltic lavas of the Asosa region of Benishangul‐Gumuz, western Ethiopia. There is widespread artisanal gold production in the Asosa region, with moderate activity by small numbers of local workers producing relatively large amounts of gold. There is a strong relationship between predominantly shear zone‐hosted gold deposits and the Kuluck shear zone, suggesting a structural control on gold accumulation. Gold is also commonly associated with secondary sulphide mineralization and magnetite alteration in Asosa rocks. The source of the gold is thought to be the sub‐volcanic intrusions generated during the subduction of the oceanic crust at the trench island‐arc system, akin to what we see today in epithermal and porphyry type gold systems. Historical workings and anomalous gold concentrations in rock, soil and stream sediments point to a potentially significant untapped gold resource in the Asosa region of western Ethiopia.     

Interpreting erosion rates from cosmogenic radionuclide concentrations measured in rapidly eroding terrain

A combination of numerical analysis and ¹⁰Be concentrations measured in sediment samples from the high‐relief Torrente catchment, southern Spain, allows us to investigate the sampling requirements for determining erosion rates using cosmogenic nuclides in high‐relief, landslide‐dominated terrain. We use simple modelling to quantify the effect of particle spalling and/or landsliding on erosion rates determined using a cosmogenic in‐situ produced isotope. Analytical results show that the cosmogenic nuclide concentration of a surface experiencing regular detachment of a grain or block may be considered to be in steady state, and ‘in‐situ’ erosion rates estimated, when an appropriate number of spatially independent samples are amalgamated. We present equations that enable calculation of the number of bedrock samples that must be amalgamated for the estimation of mean erosion rates on an outcrop experiencing regular detachment of a grain or chip of thickness L every T years. Our findings confirm that mean catchment erosion rates may be reliably estimated from ¹⁰Be concentrations in fluvial sediment in high‐relief rapidly eroding terrain. These catchment‐wide integrated erosion rates can be calculated where erosion is primarily accomplished through shallow (<3 m) spalling processes; where deep‐seated (>3 m) landslides are the dominant mode of erosion only minimum erosion rates can be determined. Lastly, we present erosion rate measurements from the Torrente catchment that reveal variation of two orders of magnitude (0·03–1·6 m ka^?1) quantifying the high degree of spatial variation in erosion rates expected within rapidly uplifting catchments. Copyright © 2006 John Wiley & Sons, Ltd.     

Fatal ingestion of floating net debris by two sperm whales (Physeter macrocephalus)

In 2008 two male sperm whales (Physeter macrocephalus) stranded along the northern California coast with large amounts of fishing net scraps, rope, and other plastic debris in their stomachs. One animal had a ruptured stomach, the other was emaciated, and gastric impaction was suspected as the cause of both deaths. There were 134 different types of nets in these two animals, all made of floating material, varying in size from 10 cm² to about 16 m². The variability in size and age of the pieces suggests the material was ingested from the surface as debris rather than bitten off from active gear. These strandings demonstrate that ingestion of marine debris can be fatal to large whales, in addition to the well documented entanglements known to impact these species.