RSS sections and groups meeting reports

Merseyside local group meeting: Anticipating extreme events

Written by Maria Sudell on . Posted in Sections and local group meeting reports

On the 6th June 2017, the RSS Merseyside local group hosted an afternoon session concerning 'Anticipating extreme events'. There were 20 people in attendance, approximately two thirds of whom were RSS members. As usual, the majority of attendees were from a range of departments at the University of Liverpool. In addition there were also attendees from United Utilities, the Health and Safety Executive, and Leeds University.

The afternoon originally was scheduled to contain two talks, however due to unforeseen circumstances, only one speaker was able to present at the event. As such, we enjoyed a fascinating talk from Professor Jonathan Rougier of Bristol University titled 'Assessing the risk from large volcanic eruptions: Understanding the historical record'.

The talk began with a description of how a volcanic eruption could affect human civilisation, namely that it is not the size of the volcano but the magnitude of the eruption that is the issue. Roughly, an eruption of magnitude 4 would constitute a problem for a region, 5 for a country, 6 for surrounding countries, 7 for the continent and 8 for the entire world (an event that would affect the entire human civilisation). So in the analysis of volcanic data, interest focuses on probability of exceedance curves – the probability of at least one eruption of at least a given magnitude within the next year. The reciprocal of this probability then gives the expected number of years to wait until such an eruption, termed the return period.

Two main issues with volcanic data that could affect estimation of these values were identified. Firstly, when the magnitudes of recorded volcanic eruptions are plotted, a rounding issue is apparent. More eruptions of integer magnitude values are recorded than non-integer values. This problem of rounding bias is eliminated only when magnitudes are binned into bins of width 1. Secondly, there is an issue with under recording of volcanic eruptions. The rate of large eruptions globally is relatively constant, and so a plot of eruptions of magnitude between (for example) 6 and 7 should produce a linear graph. However the graphs indicated an under-recording issue, with a larger amount of under recording for lower magnitudes of eruption. The best method to account for the under-recording was to use data only from the modern period, where recording of eruptions is more reliable, leading to fewer data points, but a more reliable dataset.

When these two issues are accounted for in the analysis, the estimates of the return period for a magnitude 8 eruption vary considerably to previous research. Previously, one paper reported an estimated return period for a magnitude 8 eruption as 710,000 years. In comparison, an analysis accounting for rounding bias and under reporting gave a return period for a magnitude 8 eruption of 17,000 years. As such, the question becomes 'Does policy for other risks change given that a super-eruption occurs more regularly than previously thought?'

The event concluded with a question and answer session, which covered a variety of issues from the possibility of spatial or time correlation of eruptions, to policy for eruptions, to further questions about the under-reporting issues.

The next meeting of the RSS Merseyside local group will take place on Wednesday the 11th October, and is titled 'Predicting Injuries in Sport', with first confirmed speaker Dr Sean Williams of the University of Bath. Further details of this, and all future talks, are available on the Merseyside local group website: https://sites.google.com/site/rssmerseyside/

Merseyside local group

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