Regional ash fall hazard I: a probabilistic assessment methodology
Regional ash fall hazard I: a probabilistic assessment methodology
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区域火山灰坠落灾害 I：概率评估方法
作者：
S. Jenkins;C. Magill;J. McAneney;R. Blong
火山灰是影响最深远的火山灾害之一，大规模爆炸性喷发产生的火山灰有可能影响数千公里以外的社区。对火山灰坠落造成的危害进行量化是有问题的，部分原因是由于数据有限，使火山喷发的特征不确定，但也因为火山喷发时，火山灰的分布受时间和海拔变化的风力条件控制。任何一个地点都可能受到一个或多个火山的火山灰福尔斯的影响，因此，针对火山的研究可能无法充分掌握火山灰对火山活跃地区社区的危害。在试图处理这些不确定性，本文概述了一个概率框架，在区域范围内评估灰降危害。该方法采用了随机模拟技术，所依据的是可适用于任何地区的一般原则，但在此仅适用于亚太区域。根据每座火山的喷发历史，以及在缺乏数据的情况下，根据全球类似火山的平均喷发行为，确定了该区域190座火山大于或等于火山爆炸性指数4的喷发的平均重复间隔。喷发历史来自史密森尼学会的全球火山活动计划全新世事件目录和未发表的数据，全球类似物来自同一类型的火山：火山口，大锥，盾，熔岩圆顶或小锥。模拟了190，000种可能的喷发情景，每个情景的火山灰扩散都是使用对流扩散模型和当地风力条件确定的。关键不确定性由概率分布描述。模拟结果包括超过给定灰厚度的年度概率，所有喷发情景和火山的总和。一份配套文件介绍了亚太区域取得的成果
Volcanic ash is one of the farthest-reaching volcanic hazards and ash produced by large magnitude explosive eruptions has the potential to affect communities over thousands of kilometres. Quantifying the hazard from ash fall is problematic, in part because of data limitations that make eruption characteristics uncertain but also because, given an eruption, the distribution of ash is then controlled by time and altitude-varying wind conditions. Any one location may potentially be affected by ash falls from one, or a number of, volcanoes so that volcano-specific studies may not fully capture the ash fall hazard for communities in volcanically active areas. In an attempt to deal with these uncertainties, this paper outlines a probabilistic framework for assessing ash fall hazard on a regional scale. The methodology employs stochastic simulation techniques and is based upon generic principles that could be applied to any area, but is here applied to the Asia-Pacific region. Average recurrence intervals for eruptions greater than or equal to Volcanic Explosivity Index 4 were established for 190 volcanoes in the region, based upon the eruption history of each volcano and, where data were lacking, the averaged eruptive behaviour of global analogous volcanoes. Eruption histories are drawn from the Smithsonian Institution’s Global Volcanism Program catalogue of Holocene events and unpublished data, with global analogues taken from volcanoes of the same type category: Caldera, Large Cone, Shield, Lava dome or Small Cone. Simulated are 190,000 plausible eruption scenarios, with ash dispersal for each determined using an advection–diffusion model and local wind conditions. Key uncertainties are described by probability distributions. Modelled results include the annual probability of exceeding given ash thicknesses, summed over all eruption scenarios and volcanoes. A companion paper describes the results obtained for the Asia-Pacific region