Probabilistic Volcanic Ash Hazard Analysis (PVAHA) I: development of the VAPAH tool for emulating multi-scale volcanic ash fall analysis

Abstract

Significant advances have been made in recent years in probabilistic analysis of geological hazards. Analyses of this kind are concerned with producing estimates of the probability of occurrence of a hazard at a site given the location, magnitude, and frequency of hazardous events around that site; in particular Probabilistic Seismic Hazard Analysis (PSHA). PSHA is a method for assessing and expressing the probability of earthquake hazard for a site of interest, at multiple spatial scales, in terms of probability of exceeding certain ground motion intensities. Probabilistic methods for multi-scale volcanic ash hazard assessment are less developed. The modelling framework presented here, Probabilistic Volcanic Ash Hazard Analysis (PVAHA), adapts the seismologically based PSHA technique for volcanic ash. PVAHA considers a magnitude-frequency distribution of eruptions and associated volcanic ash load attenuation relationships and integrates across all possible events to arrive at an annual exceedance probability for each site across a region of interest. The development and implementation of the Volcanic Ash Probabilistic Assessment tool for Hazard (VAPAH), as a mechanism for facilitating multi-scale PVAHA, is also introduced. VAPAH outputs are aggregated to generate maps that visualise the expected volcanic ash hazard for sites across a region at timeframes of interest and disaggregated to determine the causal factors which dominate volcanic ash hazard at individual sites. VAPAH can be used to identify priority areas for more detailed PVAHA or local scale ash dispersal modelling that can be used to inform disaster risk reduction efforts.

Probabilistic Volcanic Ash Hazard Analysis (PVAHA) II: assessment of the Asia-Pacific region using VAPAH

“…For a full account of the conceptual frame for PVAHA and the development and validation of the VAPAH algorithm, the reader is referred to the companion paper (Bear-Crozier et al 2016). A brief summary of the PVAHA framework as pertinent to the Asia-Pacific regional case study is provided below.…”

“…The VAPAH algorithm combines magnitudefrequency relationships, a catalogue of Ash Load Prediction Equations (ALPEs) and global scale meteorological conditions for a region of interest and integrates across all possible events to arrive at a preliminary annual exceedance probability for each site across the region of interest. The reader is referred to the companion paper Bear-Crozier et al (2016) for a detailed account of the development of the VAPAH algorithm. A brief summary of the VAPAH procedure is provided below and presented in Fig.…”

“…A framework for PVAHA was developed to investigate volcanic ash hazard in terms of the annual exceedance probability for each site across a region of interest (Bear-Crozier et al 2016). For a full account of the conceptual frame for PVAHA and the development and validation of the VAPAH algorithm, the reader is referred to the companion paper (Bear-Crozier et al 2016).…”

TephraProb: a Matlab package for probabilistic hazard assessments of tephra fallout

“…First, the GVP database is not a direct input to the probabilistic modelling in TephraProb and should be used as a support tool to develop eruption scenarios and identify critical ESPs with the full knowledge of the limitations and assumptions behind such databases (Biass and Bonadonna 2013;Dzierma and Wehrmann 2010;Jenkins et al 2012; Mendoza-Rosas and De la Cruz-Reyna 2008; Siebert et al 2010;Simkin and Siebert 1994). Second assessing the long-term probability of a future eruption is not trivial and should be achieved using a rigorous probabilistic framework in order to quantify and propagate various sources of uncertainties on final estimates (Bear-Crozier et al 2016;Connor et al 2003;Jenkins et al 2012;Marzocchi and Bebbington 2012;Sandri et al 2016;Sheldrake 2014;Thompson et al 2015). Probabilities resulting from a Poisson process should not be viewed as more than a first-order estimate, and only when the hypotheses of stable rate and independent events are satisfied (Borradaile 2003).…”

“…In the latter case, the hazard is quantified as a probability to exceed a given tephra accumulation and can be expressed either as conditional to the occurrence of the eruption scenario (e.g. scenariobased hazard assessment; Biass et al 2016;Bonadonna et al 2005;Scaini et al 2014;Volentik and Houghton 2015) or as absolute when the long-term probability of the eruption scenario is also quantified (Bear-Crozier et al 2016;Jenkins et al 2012;Marzocchi and Bebbington 2012;Sandri et al 2014Sandri et al , 2016Thompson et al 2015).…”