Developing probabilistic eruption forecasts for dormant volcanoes: a case study from Mt Taranaki,New Zealand     

Michael B. Turner  Shane J. Cronin  Mark S. Bebbington  Thomas Platz 《Bulletin of Volcanology》2008,70(4):507-515

The majority of continental arc volcanoes go through decades or centuries of inactivity, thus, communities become inured to their threat. Here we demonstrate a method to quantify hazard from sporadically active volcanoes and to develop probabilistic eruption forecasts. We compiled an eruption-event record for the last c. 9,500 years at Mt Taranaki, New Zealand through detailed radiocarbon dating of recent deposits and a sediment core from a nearby lake. This is the highest-precision record ever collected from the volcano, but it still probably underestimates the frequency of eruptions, which will only be better approximated by adding data from more sediment core sites in different tephra-dispersal directions. A mixture of Weibull distributions provided the best fit to the inter-event period data for the 123 events. Depending on which date is accepted for the last event, the mixture-of-Weibulls model probability is at least 0.37–0.48 for a new eruption from Mt Taranaki in the next 50 years. A polymodal distribution of inter-event periods indicates that a range of nested processes control eruption recurrence at this type of arc volcano. These could possibly be related by further statistical analysis to intrinsic factors such as step-wise processes of magma rise, assembly and storage.  相似文献   

Investigating a time‐shift extended imaging condition in a Kirchhoff pre‐stack depth migration algorithm          下载免费PDF全文

Gareth Shane O'Brien  Sean Joseph Delaney  Michael Igoe  John Doherty  Andrew Colhoun 《Geophysical Prospecting》2018,66(4):688-706

Extracting true amplitude versus angle common image gathers is one of the key objectives in seismic processing and imaging. This is achievable to different degrees using different migration techniques (e.g., Kirchhoff, wavefield extrapolation, and reverse time migration techniques) and is a common tool in exploration, but the costs can vary depending on the selected migration algorithm and the desired accuracy. Here, we investigate the possibility of combining the local‐shift imaging condition, specifically the time‐shift extended imaging condition, for angle gathers with a Kirchhoff migration. The aims are not to replace the more accurate full‐wavefield migration but to offer a cheaper alternative where ray‐based methods are applicable and to use Kirchhoff time‐lag common image gathers to help bridge the gap between the traditional offset common image gathers and reverse time migration angle gathers; finally, given the higher level of summation inside the extended imaging migration, we wish to understand the impact on the amplitude versus angle response. The implementation of the time‐shift imaging condition along with the computational cost is discussed, and results of four different datasets are presented. The four example datasets, two synthetic, one land acquisition, and a marine dataset, have been migrated using a Kirchhoff offset method, a Kirchhoff time‐shift method, and, for comparison, a reverse time migration algorithm. The results show that the time‐shift imaging condition at zero time lag is equivalent to the full offset stack as expected. The output gathers are cleaner and more consistent in the time‐lag‐derived angle gathers, but the conversion from time lag to angle can be considered a post‐processing step. The main difference arises in the amplitude versus offset/angle distribution where the responses are different and dramatically so for the land data. The results from the synthetics and real data show that a Kirchhoff migration with an extended imaging condition is capable of generating subsurface angle gathers. The same disadvantages with a ray‐based approach will apply using the extended imaging condition relative to a wave equation angle gather solution. Nevertheless, using this approach allows one to explore the relationship between the velocity model and focusing of the reflected energy, to use the Radon transformation to remove noise and multiples, and to generate consistent products from a ray‐based migration and a full‐wave equation migration, which can then be interchanged depending on the process under study.  相似文献   

Application of microcosm experiments for quantifying lateral flow and evapotranspiration on recovering bog ecotypes     

Michael M. Swenson  Shane Regan  Laurence W. Gill 《水文研究》2020,34(22):4211-4225

The importance of characterizing the ecohydrological interactions in natural, damaged/drained, and restored bogs is underscored by the importance of peatlands to global climate change and the growing need for peatland restoration. An understudied aspect of peatland ecohydrology is how shallow lateral flow impacts local hydrological conditions and water balance, which are critical for peatland restoration success. A novel method is presented using microcosms installed in the field to understand the dynamics of shallow lateral flow. Analysis of the difference in water table fluctuation inside and outside the microcosm experimental areas allowed the water balance to be constrained and the calculation of lateral flow and evapotranspiration. As an initial demonstration of this method, a series of four microcosm experiments were set up in locations with differing ecological quality and land management histories, on a raised bog complex in the midlands of Ireland. The timing and magnitude of the lateral flow differed considerably between locations with differing ecological conditions, indicating that shallow lateral flow is an important determining factor in the ecohydrological trajectory of a recovering bog system. For locations where Sphagnum spp. moss layer was present, a slow continuous net lateral input of water from the upstream catchment area supported the water table during drought periods, which was not observed in locations lacking Sphagnum. Consistent with other studies, evapotranspiration was greater in locations with a Spaghnum moss layer than in locations with a surface of peat soil.  相似文献   

Consequences of artificially opening coastal lagoons on their fish assemblages     

Shane Paul Griffiths 《International Journal of Salt Lake Research》1999,8(4):307-327

The consequences of artificially opening lagoon entrances on the fish assemblages of coastal lagoons in south-eastern Australia were investigated. Impacts of lagoon opening were assessed by comparing changes in the fish assemblages of Werri and Shellharbour Lagoons, both of which intermittently opened to the sea with that of Lake Illawarra, a third coastal lagoon which remained closed during the study period. Numbers of fish species and individuals did not differ significantly after lagoon openings at Werri Lagoon and Shellharbour Lagoon. However, higher numbers of species and individuals were found in Lake Illawarra before the other lagoons had opened. Abundances of some economically significant species (namelyMugil cephalus, Myxus elongatus andLiza argentea) significantly increased after openings, mainly due to small juveniles (<40 mm FL) recruiting to the seagrass beds. In contrast, these species were caught as larger juveniles (>70 mm FL) in Lake Illawarra. Furthermore, their abundance in Lake Illawarra declined during successive months, coinciding with declining salinity. Abundances of resident species (such asPseudomugil olorum andAfurcagobius tamarensis) remained largely unchanged after openings. Although it was clear that marine-spawning species must benefit from lagoon openings, the number and composition of species able to move into lagoons from adjacent waters may be dependent upon the frequency, duration and time of year that the entrance is connected to the sea. The present study thus provides data which may be useful for fisheries management in intermittently open lagoons. However, these results should not be cited as reason to artificially open lagoon entrances as further detailed studies of other aspects of lagoon biota, such as their invertebrate and avian faunas, are also needed to provide sufficient basis for broader management frameworks.  相似文献   

Interpreting Auckland’s volcanic governance through an institutional lens     

Catherine Murray  Garry McDonald  Shane Cronin 《Natural Hazards》2015,75(1):441-464

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Contamination level of mercury in red meat products from cetaceans available from South Korea markets     

Endo T  Yong-Un M  Baker CS  Funahashi N  Lavery S  Dalebout ML  Lukoschek V  Haraguchi K 《Marine pollution bulletin》2007,54(6):669-677

Levels of total mercury (T-Hg) were surveyed in red meat (n=73) and liver (n=3) from toothed whales, dolphins and porpoises (odontocetes) sold for human consumption in the coastal cities of South Korea. High concentrations of T-Hg were found in the liver products of finless porpoises (18.7 and 156 microg/wet g) and common dolphins (13.2 microg/wet g). The T-Hg concentrations in red meat products were highest in the false killer whale (9.66+/-12.3 microg/wet g, n=9), bottlenose dolphin (10.6+/-12.6 microg/wet g, n=3) and killer whale (13.3 microg/wet g, n=1), and lowest in Cuvier's beaked whale and the harbour porpoise (0.4-0.5 microg/wet g). Thus, most of the products that originated from odontocetes exceeded the safety limit of 0.5 microg/wet g for T-Hg set by the South Korean health authorities for the fishery industry. Pregnant women and other vulnerable sectors of the population living in South Korea should therefore limit their consumption of odontocete products.  相似文献   

Impacts on agriculture following the 1991 eruption of Vulcan Hudson, Patagonia: lessons for recovery   总被引：1，自引：1，他引：0  

Thomas Wilson  Jim Cole  Shane Cronin  Carol Stewart  David Johnston 《Natural Hazards》2011,57(2):185-212

Large explosive eruptions have the potential to distribute heavy ashfalls across large areas, resulting in physical and chemical impacts on agriculture, and economic and psycho-social impacts on rural communities. This study investigates how affected agriculture and rural communities have adapted, absorbed and mitigated impacts following a range of ashfall thicknesses (>2 m?C<1 mm) from the 12?C15 August 1991 eruption of Vulcan Hudson, one of the largest eruptions of the twentieth century. An estimated 1 million livestock died after the eruption due to pasture burial by ashfall and ongoing suppression of vegetation recovery. Horticulturalists suffered ongoing damage to crops from wind-blown ash and changes to soil properties increased irrigation and cultivation requirements. Real or perceived impacts on human health and impacts on farm productivity from the ashfall resulted in evacuation of farms and small towns in the short term. Long-term farm abandonment occurred in areas of heavy ashfall (upper Ibáñez valley) and highly stressed farming systems, even where ashfall was relatively thin (<50 mm), such as the Argentine steppe. The mono-agricultural system of sheep farming in the steppe region had few options other than destocking, proving less resilient than the diverse high-intensity horticultural and pastoral mix in irrigated valleys, which allowed more rapid adaption through diversification of production. Farms with natural advantages and greater investment in capital improvements led to greater damage potential initially (at least in cost terms), but ultimately provided a greater capacity for response and recovery. Better soils, climate and significantly greater access to technological improvements such as cultivation tools, irrigation and wind breaks were advantageous, such as at Chile Chico (Chile), Los Antiguos and Perito Moreno (Argentina). Cultivation increased chemical and physical soil fertility, especially when used in combination with fertilisation and irrigation. Appropriate use of seeds and cropping techniques within the new soil and growing conditions was important. Government agencies had a vital role in the dissemination of information for appropriate farm management responses, ash chemistry analysis, evacuations and welfare, and in the longer term to provide technical and credit assistance to facilitate recovery.  相似文献   

Gravitational wave bursts from the Galactic massive black hole     

Clovis Hopman  Marc Freitag  Shane L. Larson 《Monthly notices of the Royal Astronomical Society》2007,378(1):129-136

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Contrasting punctuated zircon growth in two syn-erupted rhyolite magmas from Tarawera volcano: Insights to crystal diversity in magmatic systems     

Sonja Storm  Phil Shane  Axel K. Schmitt  Jan M. Lindsay 《Earth and Planetary Science Letters》2011,301(3-4):511-520

Two mineralogically and chemically distinct rhyolite magmas (T1 and T3) were syn-erupted from the same conduit system during the 21.9 ka basalt intrusion-triggered Okareka eruption from Tarawera volcano, New Zealand. High spatial resolution U–Th disequilibrium dating of zircon crystals at the ~ 3–5 μm scale reveals a protracted yet discontinuous zircon crystallization history within the magmatic system. Both magma types contain zircon whose interiors predate the eruption by up to 200 ka. The dominant age peak in the T1 magma is ~ 30 ka with subordinate peaks at ~ 45, ~ 75, and ~ 100 ka, whereas the T3 magma has a dominant zircon interior age peak at ~ 90 ka with smaller modes at ~ 35 and ~ 150 ka. These patterns are consistent with isolated pockets of crystallization throughout the evolution of the system. Crystal rim analyses yield ages ranging from within error of the eruption age to at least ~ 90 ka prior to eruption, highlighting that zircon crystallization frequently stalled long before the eruption. Continuous depth profiling from crystal rims inward demonstrates protracted growth histories for individual crystals (up to ~ 100 ka) that were punctuated by asynchronous hiatuses of up to 30 ka in duration. Disparate zircon growth histories can result from localized thermal perturbations caused by mafic intrusions into a silicic reservoir. The crystal age heterogeneity at hand-sample scale requires considerable crystal transport and mixing. We propose that crystal mixing was achieved through buoyancy instabilities caused by mafic magma flow through crystal mush. A terminal pre-eruptive rejuvenation event was capable of mobilizing voluminous melts that erupted, but was too short (< 10²–10³ years) to result in extensive zircon growth. The contrasting, punctuated zircon histories argue against closed-system fractional crystallization models for silicic magmatism that require protracted cooling times following a mostly liquid starting condition.  相似文献   

A Test of Central Place Theory Using Shuttle Imaging Radar (SIR‐A) of China's North Central Plain     

Christopher Shane Davies  Robert K. Holz  David Robertus 《国际地球制图》2013,28(1):14-23

Abstract

This study utilizes radar imagery to test the application of Walter Christaller's central‐place theory on China's North Central Plain. Examination of the spatial order and layout of settlements reveal that central place theory's transportation principle, k=4 exists. The study distinguishes four hierarchical settlement sizes and shows how effective rural societies are in evolving settlement structures whose spatial order and regularity avoids spatial inefficiencies. The advent of space based imaging systems such as SIR‐A radar imagery has permitted tests of new sites where the restrictive conditions of central place theory exist. These studies allow parallels to be drawn between the postulates of this theory of settlement structure and whether the theory is matched in reality.

This work is needed because of such scarcities. It allows the theory to undergo further subjections, a scrutiny needed for the validation, or otherwise of its postulates. The work adds to a large body of literature on this topic whose limitation has been the scarcity of actual test sites where theory and reality can be compared. The study presents positive indications that central place theory exists in reality, a compliment to the remarkable perceptions of Walter Christaller.  相似文献