The quest for wisdom: lessons from 17 tsunamis, 2004–2014

Abstract

Since the catastrophic Sumatra–Andaman tsunami took place in 2004, 16 other tsunamis have resulted in significant damage and 14 in casualties. We review the fundamental changes that have affected our command of tsunami issues as scientists, engineers and decision-makers, in the quest for improved wisdom in this respect. While several scientific paradigms have had to be altered or abandoned, new algorithms, e.g. the W seismic phase and real-time processing of fast-arriving seismic P waves, give us more powerful tools to estimate in real time the tsunamigenic character of an earthquake. We assign to each event a ‘wisdom index’ based on the warning issued (or not) during the event, and on the response of the population. While this approach is admittedly subjective, it clearly shows several robust trends: (i) we have made significant progress in our command of far-field warning, with only three casualties in the past 10 years; (ii) self-evacuation by educated populations in the near field is a key element of successful tsunami mitigation; (iii) there remains a significant cacophony between the scientific community and decision-makers in industry and government as documented during the 2010 Maule and 2011 Tohoku events; and (iv) the so-called ‘tsunami earthquakes’ generating larger tsunamis than expected from the size of their seismic source persist as a fundamental challenge, despite scientific progress towards characterizing these events in real time.

Tsunamis: bridging science, engineering and society

“…Validation of these laws, in the context of the widely used dislocation models would require pre-and post-event bathymetric measurements at sufficient resolution to allow for resolving 1 m seafloor displacements in thousands of metres of water depth. At any rate, the 2011 earthquake, with its coseismic displacement locally reaching 60 m, violates any interpretation of scaling laws, however stretched [27]. 2 It is thus quite clear that seismic inversions are not sufficient for accurate real-time forecasts for the largest of earthquakes, likely to have the most impact.…”

“…It was followed by the 12 December 1992 Flores tsunami, and by other tsunamis striking about once a year, on average, somewhere in the world. Most with run-up heights over 2 m were surveyed to measure inundation and run-up data, and allowing studies in detail of their parent earthquakes and tsunamis they triggered [27,34]. The Nicaraguan tsunami had three remarkable features.…”

“…Among them, the proposed control of maximum earthquake magnitude at subduction [96]. The seismic moment, epicentre location and earthquake mechanism are routinely determined in real time through the centroid moment tensor solution, except when they are not, the 2004 and later the 2011 events being good examples [27,97]. In addition, seismic scaling laws, relating earthquake magnitude to fault length, width and duration of rupture (essentially reducing the characterization of the earthquake to a single parameter) have not been confirmed for subduction zone mega events, especially regarding the so-called tsunami earthquakes, whose rupture velocities are significantly deficient.…”

“…The scientific challenge for mitigating the effects of tsunami hazards is perhaps best articulated by Okal [27]. He writes that 'our quest for wisdom in the management of tsunami hazard shares some conceptual philosophy with Zeno of Elea's paradox: like Achilles, our communities seem well armed to constantly gain in wisdom and progress towards mitigation of a perceived level of tsunami hazard, but individual new events often bring an element of diversity which redefines the goal, and like the Tortoise, keeps pushing it forward, in an everlasting challenge'.…”

“…We note that Bernard & Robinson [28] published the first textbook documenting the use of deep-ocean tsunami measurements to forecast real-time flooding along the coastline, while recently, Kânoglu & Synolakis [29] presented advances in validated and verified numerical codes for prediction of tsunami evolution and mitigation. To paraphrase Okal [27], our objective in what follows is to gain in wisdom and progress towards effective hazard mitigation, pursuing key recent events from which we learned, and which we think we understand better than earlier ones. …”