Browsing by Author "Whittaker, AK"

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    Earthquake hazard assessment uncertainty reduced by fragile geologic features in coastal Central California
    (Copernicus GmbH, 2020-05-04) Caklias, A; Rood, DH; Stirling, M; Madugo, C; Abrahamson, NA; Wilcken, KM; Gonzalez, T; Kottke, A; Whittaker, AK; Page, W; Stafford, P
    Probabilistic seismic hazard analysis (PSHA) models typically provide estimates of ground motions for return periods that exceed historical observations. It is therefore important to develop quantitative methods to evaluate and refine ground motion estimates for long return periods, especially in proximity to major earthquake sources where estimates can be very high. Here we provide empirical constraints over 10,000s years on ground motions from onshore and offshore seismic sources in central California using the distribution, age and fragility (probability of toppling given an intensity of ground shaking) of fragile geologic features. The fragility is estimated for seven precariously balanced rocks (PBRs) formed on uplifted marine terrace palaeo-sea stacks. The site is <10 km from the Hosgri fault, a major offshore fault considered part of the San Andreas fault system. PBR 3D models were constructed using photogrammetry and used to define normalized geometric measures that could be combined with empirical models to estimate the probability of toppling (i.e., fragility), over a range of vector ground motions (PGA and PGV/PGA). Using vector hazard and the fragility, the likelihood of survival was then computed. The PGA associated with a 50 percent chance of survival varies from ~0.4-1.3 g for the selected PBRs. We obtain fragility ages (time that each PBR achieved its current geometry) using Be-10 cosmogenic surface exposure dating. Extremely low Be-10 concentrations (~5000 at/g) in modern high-stand samples demonstrates minimal inheritance and reliability of chert age estimates. Additionally, the volume of colluvium surrounding the palaeo-sea stack outcrops, determined from LiDAR, combined with alluvial fan surface dating (using Be-10 and soil profile development indices) indicates low erosion rates (~2.5 mm/ky) and long-term stability. Exposure ages that bound the fragility age by approximating the removal of surrounding blocks range ~17-95 ky. The similar age distributions of block removal events around all of features suggests that all PBRs share a common evolution, and we interpret ~21 ka as the most defensible fragility age estimate of all seven PBRs, with negligible change to their fragility between that time and now. Despite the lack of constraints on the recurrence behaviour of the Hosgri Fault, the slip rate is such that the PBRs have almost certainly experienced multiple large-magnitude, near-field earthquakes, and therefore provide rare constraints on low frequency ground motions. Each estimate output from the PSHA model is evaluated against the ground-motion corresponding to the 95% probability of survival of the most fragile PBR over the 21 ka fragility age. The logic tree branches that produce estimates inconsistent with the survival of the PBR are removed from the PSHA model. From the consistent logic tree branches a new PSHA model is produced that has reduced mean ground-motion levels and reduced uncertainty between the estimates. At the 10-4 hazard level, the mean ground motion estimate is reduced by ~30% and the range of estimated 5th-95th percentile ground motions is reduced by ~50%. © Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 Licence.
  • No Thumbnail Available
    Item
    Hydration induced structural changes in native, denatured and protected soy glycinin (11s)
    (Institute of Food Technologists, 2007-07) Appelqvist, IAM; Rout, MK; Chanvrier, H; Dezfouli, M; Kelly, M; Htoon, AK; Kealley, CS; Gilbert, EP; Strounina, E; Whittaker, AK; Gidley, MJ; Lillford, PJ
    Proteins and other biomolecules undergo a dynamic transition to a glass-like solid state with small atomic fluctuations. This dynamic transition can inhibit biological function and alter their material properties.
  • Thumbnail Image
    Item
    Hydration of paper studied with solid-state magnetisation-exchange H-1 NMR spectroscopy
    (Walter de Gruyter, 2006-07) Garvey, CJ; Parker, IH; Simon, GP; Whittaker, AK
    The wide-line H-1 nuclear magnetic resonance (NMR) spectrum of paper in equilibrium with ambient humidity consists of super-imposed relatively broad and narrow lines. The narrower line is of the order of 2 kHz wide at half the maximum height, while the broader line is of the order of 40 kHz in width at half height. On the basis of these line widths, the narrow line is assigned to water sorbed to the paper, and the broad line to the polymeric constituents of the paper. It was not possible to distinguish between the various polymeric components of paper contributing to the H-1 NMR spectra. A modified Goldman-Shen pulse sequence was used to generate a spatial magnetisation gradient between the polymer and water phases. The exchange of magnetisation between protons associated with water and those associated with the macromolecules in paper was observed. The exchange of magnetisation is discussed within a heat transfer model for homonuclear dipolar coupling, with exchange being characterised by a spin-diffusion coefficient. Consideration of the magnitude of the initial rate of the exchange process and estimates of the spin-spin relaxation times based on H-1 line widths indicate that some water must exist in a sufficiently immobile state as to allow homonuclear dipolar interactions between adjacent polymer and water protons. Thus, water sorbed onto paper must exist in at least two states in mass exchange with each other. This observation allows certain conclusions to be drawn about the ratio of free/bound water as a function of moisture content and the dispersal of water within the polymer matrix. © 2006, Walter de Gruyter
  • No Thumbnail Available
    Item
    Structure and molecular mobility of soy glycinin in the solid state
    (American Chemical Society, 2008-10) Kealley, CS; Rout, MK; Dezfouli, MR; Strounina, E; Whittaker, AK; Appelqvist, IAM; Lillford, PJ; Gilbert, EP; Gidley, MJ
    We report a multitechnique study of structural organization and molecular mobility for soy glycinin at a low moisture content (<30% w/w) and relate these to its glass-to-rubber transition. Small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy are used to probe structure and mobility on different length and time scales. NMR (similar to 10(-6) to 10(-3) s) reveals transitions at a higher moisture content (> 17%) than DSC or SAXS, which sample for much longer times (similar to 10 to 10(3) s) and where changes are detected at > 13% water content at 20 degrees C. The mobility transitions are accompanied by small changes in unit-cell parameters and IR band intensities and are associated with the enhanced motion of the polypeptide backbone. This study shows how characteristic features of the ordered regions of the protein (probed by SAXS and FTIR) and mobile segments (probed by NMR and DSC) can be separately monitored and integrated within a mobility transformation framework. © 2008, American Chemical Society
  • No Thumbnail Available
    Item
    Surface-functionalized polymer nanoparticles for selective sequestering of heavy metals
    (Wiley-VCH Verlag Berlin, 2006-03) Bell, CA; Smith, SV; Whittaker, MR; Whittaker, AK; Gahan, LR; Monteiro, MJ
    Xanthate-mediated (reversible addition-fragmentation chain transfer) emulsion polymerization has been used to create novel polystyrene nanoparticles with functionalized surfaces (see Figure) for the selective sequestering of heavy metals from water below ppm levels. These nanoparticles show a high degree of selectivity for HgII over CoII. This technology has potential for the selective remediation of heavy metals from the human blood system. © 2006, Wiley-VCH Verlag Berlin