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Earthquake hazards and risks – some selective, provocative thoughts SAPPUR, Bristol 15 – 17 September 2009 Willy Aspinall, Earth Sciences, Bristol University

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Earthquakes have claimed several million human lives over the last two millenia … due to application of earthquake codes and better construction techniques? Or a short-term statistical fluctuation? But recent urban growth has been accompanied by a decline in fatality rate when expressed as a percentage of instantaneous population…. The recent annualised average global fatality count from earthquakes has been about 100,000/year, a rate that is determined mainly by the larger but less frequent seismic disasters Half worlds population now lives in cities and a significant number of these cities are located in earthquake-prone regions An increasing fraction of the worlds population reside in poorly-constructed dwellings with high susceptibility to seismic damage - building collapses accounting for more than 75% of human casualties in earthquake Some basic remarks:

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Probabilistic seismic hazard assessment Long record of UK methodological advances, but mostly unpublished and inaccessible Basic hazard calculational model unchanged from Cornell 1968…major simplifying assumptions and data transformations to make problem tractable (Gutenberg-Richter relation)… New insights into earthquake processes and occurrence relations have potential implications for seismic hazard assessment Of considerable importance (in common with other hazards) is the need to comprehend the role and best statistical treatment of uncertainties in real data …. not beyond the bounds of credibility that earthquake prediction could be advanced by such work – very very contentious. More fundamental problems: hidden thrust faults; issues of expert judgment and quantifying uncertainties…..

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Prediction, forecasting and warnings of imminent earthquakes ……TIPcasting: development of ways to assimilate different strands of evidence (e.g. seismicity patterns, radon, stress transfer, geodetic strain changes – multidisciplinary networking) On the seismological edge……. Traditionally, seismologists have eschewed earthquake forecasting in the absence of certainty. Investigation of ways to measure forecast skill in probabilistic hazard assessment, and issues of estimating and minimizing false positive rates for earthquake predictions Issues of scientific acceptability of research into earthquake prediction sensu lato

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Fault heterogeneity and earthquake scaling; stress transfer relations among faults and earthquakes (e.g. Steacy, McCloskey & colleagues) Conventional research NERC should continue to fund…. Long-range elastodynamic interactions of faults and hidden micro- correlations - important for insurance portfolio losses

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