Browsing by Author "Clark, K"

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    Deposits, flow characteristics, and landscape change resulting from the September 2009 South Pacific Tsunami in the Samoan Islands
    (Elsevier Science, 2011-07-01) Richmond, B; Buckley, M; Etienne, S; Chagué-Goff, C; Clark, K; Goff, JR; Dominey-Howes, D; Strotz, L
    The September 29th 2009 tsunami caused widespread coastal modification within the islands of Samoa and northern Tonga in the South Pacific. Preliminary measurements indicate maximum runup values of around 17 m (Okal et al., 2010) and shore-normal inundation distances of up to similar to 620 m (Jaffe et al., 2010). Geological field reconnaissance studies were conducted as part of an UNESCO-IOC International Tsunami Survey Team survey within three weeks of the event in order to document the erosion, transport, and deposition of sediment by the tsunami. Data collected included: a) general morphology and geological characteristics of the coast, b) evidence of tsunami flow (inundation, flow depth and direction, wave height and runup), c) surficial and subsurface sediment samples including deposit thickness and extent, d) topographic mapping, and e) boulder size and location measurements. Four main types of sedimentary deposits were identified: a) gravel fields consisting mostly of isolated cobbles and boulders, b) sand sheets from a few to similar to 25 cm thick, c) piles of organic (mostly vegetation) and man-made material forming debris ramparts, and d) surface mud deposits that settled from suspension from standing water in the tsunami aftermath. Tsunami deposits within the reef system were not widespread, however, surficial changes to the reefs were observed. Published by Elsevier B.V.
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    Lacustrine paleoseismometers reveal spatial and temporal patterns of rupture during the last ten large earthquakes on the Alpine Fault, New Zealand
    (American Geophysical Union, 2014-12-19) Howarth, JD; Fitzsimons, SJ; Langridge, R; Clark, K; Cochran, UA; Norris, RJ; Jacobsen, GE
    The rarity of long, well-dated paleoseismic records from sites along plate boundary transform faults is a major constraint on the development and evaluation of conceptual models of fault rupture behaviour. This is the case for the 800 km long, high slip rate (27±5 mm yr-1), dextral strike-slip Alpine Fault at the boundary between the Pacific and Australian plates in southern New Zealand. We use lacustrine paleoseismology to evaluate the hypothesis that the Alpine Fault exhibits self-similar behaviour, that is, the fault always produces earthquakes at or near a maximum magnitude of Mw8. The hypothesis is tested using reconstructions of high intensity shaking from five lakes situated along 240 km of the Alpine Fault's Central section. Sedimentological investigation of lake cores shows that high intensity shaking events are recorded in the lake sediments as turbidites formed by subaqueous slumping. These turbidites are overlain by terrigenous sediment from co- and post-seismic landsliding on hillslopes in the lakes' mountainous catchments. Chronologies derived from Bayesian modelling of AMS 14C dates on terrestrial leaf macrofossils precisely constrain the timing of earthquakes at the lake sites, facilitating along-strike correlation. Shaking events correlate between the sites and with known ruptures of the Alpine Fault, confirming the seismic origin of the deposits and allowing thresholds of shaking intensity for deposit formation to be determined using isoseismal modelling. Modelled shaking intensities for the last two Alpine Fault earthquakes show that subaqueous slumping occurs when shaking intensities exceed Modified Mercalli scale (MM) VI-VII, and that increased fluvial sediment fluxes from earthquake-induced landslides occur when shaking intensities exceed MM IX. The record of synchronous MM IX shaking at the lake sites provides first order constraint on the rupture length of the last ten earthquakes on the central Alpine Fault. Rupture scenarios for these earthquakes are augmented by correlating event timing with long earthquake records from the South Westland section and geomorphic reconstructions of the slip distribution for the most recent ruptures to explore the best-fit model of fault behaviour and to test the hypothesis that the Alpine Fault always ruptures in great (Mw8) earthquakes.
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    The use of boulders for characterising past tsunamis: lessons from 2004 Indian Ocean and 2009 South Pacific tsunamis
    (Elsevier, 2011-07-01) Etienne, S; Buckley, M; Paris, R; Nandasena, AK; Clark, K; Strotz, L; Chagué-Goff, C; Goff, JR; Richmond, B
    Tsunamis are high energy events capable of transporting extremely heavy loads including boulders. We compare boulder deposits created by two modern tsunami events, the 2004 Indian Ocean and the 2009 South Pacific tsunamis, where the boulder sources were in similar topographic settings, and for which we have accurate data on the wave characteristics. Boulder distribution, preferential orientation and numerical simulation of boulder transport are discussed. A comparison between the impacts of the South Pacific and Indian Ocean tsunamis shows similar characteristics, such as limited landward extent and the absence of landward fining. Differences between the results from modelling and field data are most probably caused by variables such as coastal plain roughness (buildings, trees), microtopography, particle shape, and boulder collision during transport that are summarised as coefficients in the mathematical models. Characterising modern events through coarse sediment deposits provides valuable information to help identify and interpret palaeo-tsunami imprints on coastal landscapes. (C) 2011 Elsevier B.V.