Presentations

IDRC 2014, Davos, Switzerland, August 28, 2014

Session on “Global Disasters: Addressing the Risk Associated with Extreme Geohazards”

Organized by the GHCP.

Recognizing, Imperfectly Assessing, and Partially Mitigating Extreme Geohazards in the Presence of Deep Uncertainty

Seth Stein, Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208 USA

The great earthquake that struck Japan's Tohoku coast on March 11, 2011, was much larger than predicted by sophisticated hazard models, and so caused a tsunami that overtopped giant seawalls. An immediate question that arose was if and how coastal defenses should be rebuilt, because the defenses fared poorly and building ones to withstand tsunamis as large as March 2011's is too expensive. A similar issue soon arose along the Nankai Trough to the south, where new estimates warning of giant tsunamis 2-5 times higher than in previous models raised the question of what to do, given that the timescale on which such events may occur is unknown and likely to be of order 1000 years. In one commentator's words, "the question is whether the bureaucratic instinct to avoid any risk of future criticism by presenting the worst case scenario is really helpful... What can (or should be) done? Thirty meter seawalls do not seem to be the answer." The policy question, in the words of Japanese economist H. Hori, is “What should we do in face of uncertainty? Some say we should spend our resources on present problems instead of wasting them on things whose results are uncertain. Others say we should prepare for future unknown disasters precisely because they are uncertain.”

This situation illustrates the problem we face in dealing with extreme geohazards. Typically, these involve deep uncertainties, which arise when the probabilities of outcomes are poorly known, unknown, or unknowable. This occurs when we have multiple possible models with poorly known parameters, either because we do not adequately understand the system or it has inherently unpredictable elements. In such situations, past events may give little insight into future ones. We are faced with the challenge of how much resources to divert from other needs to prepare for possible highly destructive events whose probabilities we cannot usefully assess. Hence in addition to improving scientific knowledge to reduce uncertainty, we need new decision making approaches to find sensible solutions given deep uncertainty.


Last edited 02 December 2016
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