Tsunamigenic Earthquakes: Past and Present Milestones

Abstract

We review a number of events which, taken individually, have significantly affected our understanding of the generation of tsunamis by earthquake sources and our efforts at mitigating their hazards, notably through the development of warning algorithms. Starting with the 1700 Cascadia earthquake, we examine how significant tsunamis have changed our views in fields as diverse as seismotectonics, the diversity of earthquake cycles, the development of warning algorithms, the response of communities at risk to warnings, and their education, the latter being either formal or rooted in ancestral heritage. We discuss in detail lessons from the 2004 Sumatra disasters and review the performance of warning centers and the response of affected populations during the nine significant tsunamis which have taken place since 2004.

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

“…Following a similar approach, Okal [68] has used an algorithm developed in the context of the discrimination of man-made explosions as recorded on hydroacoustic signals [69] to characterize source duration through a parameter τ 1/3 expressing the time that the envelope of a teleseismic P wave filtered along Ni et al's [61] protocol is sustained at more than one-third its maximum amplitude. Then E and τ 1/3 can be compared through the parameter Φ = log 10 τ 1/3 − 1 3 log 10 E + 5.86 (2.3) (τ 1/3 in seconds, E in ergs), which should be invariant under scaling laws and with the constant (5.86) adjusted to give it a zero average value.…”

“…Then E and τ 1/3 can be compared through the parameter Φ = log 10 τ 1/3 − 1 3 log 10 E + 5.86 (2.3) (τ 1/3 in seconds, E in ergs), which should be invariant under scaling laws and with the constant (5.86) adjusted to give it a zero average value. In the case of 'tsunami earthquakes', τ 1/3 is expected to be anomalously long, while E should be deficient, both properties resulting in an increase in Φ, which reaches values in excess of 0.35 and as high as 1.5 [68], and can thus serve as an efficient discriminant for this class of events. Finally, Lomax & Michelini [70] have used a somewhat more intricate approach in which they reconstruct an estimate of the earthquake's moment from E and a duration T R from the square root of the product (ET 3 R ), and then compare this energy-derived estimate to other determinations of the moment (presumably made at lower frequencies) to detect any anomalous behaviour in the source.…”

“…The wisdom index is simply colour-coded from 'black' (abysmal) through red (bad), yellow (average), blue (fair) and green (good). It was introduced in our previous publication [68], to which the reader is referred; however, here we simplify its concept by suppressing the intermediate orange colour between red and yellow, and the ultimate (gold) level, now combined with green. We further reclassify the lone 'olive' rating as 'blue', and we obviously extend the grading to the events postdating Okal [68], most notably to the 2011 Tohoku disaster.…”

“…It was introduced in our previous publication [68], to which the reader is referred; however, here we simplify its concept by suppressing the intermediate orange colour between red and yellow, and the ultimate (gold) level, now combined with green. We further reclassify the lone 'olive' rating as 'blue', and we obviously extend the grading to the events postdating Okal [68], most notably to the 2011 Tohoku disaster. As detailed in Okal [68], we emphasize that the assignment of the index is based not on quantitative measurements (e.g.…”

“…We start by recapping the events of the years 2004-2010, which were covered in Okal [68], to which the reader is referred for a more detailed discussion: -The 2004 Sumatra-Andaman event gets a blackstar, on account of the total absence of warning, especially for far-field shores, where many deaths could have been prevented. In addition, informal real-time warnings transmitted to government authorities in Thailand were not heeded, allegedly on account of their potentially negative impact on the large tourist community.…”