Estimating Fatality Rates for Earthquake Loss Models (2016)Emily So, by R J S Spence

But why Poets’ Corner? Well, Lewis was a poet as well. One of his poems was set to music by Paul Mealor and sung by the choir in the Abbey service. But the best answer to this question is for us to read the two contributions by Malcolm Guite and the two by the Master. Both Guite and Williams are, of course, themselves poets. They emphasise the power of words, not just of poetry, but of rhetoric and all literature, to express and convey the deepest truths. After all, the sentence inscribed round the memorial stone comes from Lewis’s marvellous essay, ‘Is Theology Poetry?’.

Brian Hebblethwaite (1963)

EMILY SO, Estimating Fatality Rates for Earthquake Loss Models (Springer 2016, 76pp)

In our technologically sophisticated world, earthquakes still regularly cause tragic loss of life and damage on a massive scale; and as Emily So rightly points out in the preface to this book, it is not the earthquakes themselves which kill, it is for the most part poorly built buildings and infrastructure. The first step to improving matters is to identify which communities and buildings are most at risk, so that they can be targeted for upgrading or replacement, and this is the aim of earthquake loss modelling. Earthquake loss models are complex structures, depending at least on seismological data on expected future earthquake magnitudes and recurrence frequencies, on engineering data on the resulting ground motion and the likely behaviour of buildings, and on medical data on the types and causes of casualties. Earthquake magnitude, location, ground motion prediction, building vulnerability and consequent casualties are all uncertain, so inevitably the resulting casualty estimate has a huge uncertainty attached to it; or, worse, it may be completely wrong if the simple cause-and-effect assumptions of the model are incorrect.

Emily So has been studying the causes of earthquake casualties and the estimation of casualty rates in earthquakes since the 2005 Kashmir earthquake in Pakistan, which killed some 80,000 people, first as a PhD study, then as a Mendenhall Research Fellow at the US Geological Survey, and subsequently with co-workers worldwide in the development of the Global Earthquake Model. The work has involved detailed investigations into the casualties in 25 fatal events over the last 40 years, many of them including post-earthquake fieldwork by the author. The book has relatively modest aims: it sets out

primarily to summarise what has been learnt, with the aim of improving future earthquake loss models.

At its heart is a review of the performance in earthquakes of buildings of each of the principal structural materials found worldwide, brick and mud masonry, timber, reinforced concrete and steel – how they fail and what are the ways in which their occupants are killed or injured – leading to some approximate estimates of casualty rates for different types of buildings once their structure fails. These are the kind of numbers which loss modellers will be glad to have and to make use of.

But Emily So also offers some important warnings about the use of such numbers. She points out that variations in the earthquake wave transmission through the underlying rock formation can dramatically alter the impact of a given size of earthquake, as happened in the 2015 Gorkha earthquake in Nepal, leading to a much lower than expected death toll; and that an earthquake’s shaking pattern may contain a warning low-level tremor which gives many occupants time to run outside, again limiting the number of casualties; and again that deaths in earthquakes from many factors other than building collapse (including landslides, and tsunamis as in Japan in 2011) have to be considered. Even more problematic for modellers is the frequent observation that a high proportion of all the deaths may occur in just a few buildings – sometimes historic but vulnerable places of worship like a cathedral or a mosque – rendering the whole idea of average casualty rates meaningless.

This book can and will be taken as a valuable set of quantitative data to improve future loss models: but viewed in a different way it constitutes a powerful critique of present approaches to loss modelling, and offers some suggestions of some additional factors they will need to incorporate if they are to provide credible loss estimates in the future.

R J S S