Abstract
The 2011 Tohoku earthquake and tsunami motivated an analysis of the potential for great tsunamis in Hawai‘i that significantly exceed the historical record. The largest potential tsunamis that may impact the state from distant, Mw 9 earthquakes—as forecast by two independent tsunami models—originate in the Eastern Aleutian Islands. This analysis is the basis for creating an extreme tsunami evacuation zone, updating prior zones based only on historical tsunami inundation. We first validate the methodology by corroborating that the largest historical tsunami in 1946 is consistent with the seismologically determined earthquake source and observed historical tsunami amplitudes in Hawai‘i. Using prior source characteristics of Mw 9 earthquakes (fault area, slip, and distribution), we analyze parametrically the range of Aleutian–Alaska earthquake sources that produce the most extreme tsunami events in Hawai‘i. Key findings include: (1) An Mw 8.6 ± 0.1 1946 Aleutian earthquake source fits Hawai‘i tsunami run-up/inundation observations, (2) for the 40 scenarios considered here, maximal tsunami inundations everywhere in the Hawaiian Islands cannot be generated by a single large earthquake, (3) depending on location, the largest inundations may occur for either earthquakes with the largest slip at the trench, or those with broad faulting over an extended area, (4) these extremes are shown to correlate with the frequency content (wavelength) of the tsunami, (5) highly variable slip along the fault strike has only a minor influence on inundation at these tele-tsunami distances, and (6) for a given maximum average fault slip, increasing the fault area does not generally produce greater run-up, as the additional wave energy enhances longer wavelengths, with a modest effect on inundation.
Highlights
This analysis is the basis for creating an extreme tsunami evacuation zone, updating prior zones based only on historical tsunami inundation
The March 11, 2011, great Tohoku earthquake and tsunami in Japan served as a wake-up call to coastal communities in the Pacific, re-emphasizing the lesson learned in the Indian Ocean in 2004: the potential for a giant Mw 9 earthquake to inflict a devastating tsunami both locally and across the ocean
As TV showed in real time, the tsunami waves approaching the Japanese coast, overtopping the carefully planned and constructed system of seawalls, inundating cities and the countryside, and severely damaging a nuclear power plant, the question posed by Butler (2012) is whether Hawai‘i is prepared for a worst-case scenario like Tohoku
Summary
The March 11, 2011, great Tohoku earthquake and tsunami in Japan served as a wake-up call to coastal communities in the Pacific, re-emphasizing the lesson learned in the Indian Ocean in 2004: the potential for a giant Mw 9 earthquake to inflict a devastating tsunami both locally and across the ocean. Often lethal, have impacted Hawai‘i from Japan, Kamchatka, the Aleutian Islands, Alaska, and Chile (Fig. 1). These events include 4 of the 5 largest earthquakes (Mw C 9) since the invention of the Richter scale—the 5th occurred in the Indian Ocean—the largest earthquakes have not produced Hawai‘i’s largest tsunamis. This distinction belongs to the two Mw 8.6 events in the Aleutian Islands (Fig. 2).
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