The Richter scale was developed to measure the magnitude of earthquakes and tops out at 10 – this being an epic event that has not yet happened. The more modern MMS (moment magnitude scale) has no upper limit, but by either system the great Alaska earthquake of 1964 registered over 9 and was then the second-largest megathrust quake then recorded (the biggest being Chile’s Valdivia earthquake four years previously).
Had this violent four-minute event taken place within shaking distance of a major population center, the consequences would have been unimaginable, with casualties up with the tens or even hundreds of thousands claimed by history’s few super-quakes. As it was, the epicenter was off the mouth of College Fjord in the Prince William Sound region of thinly populated Alaska. But while the death toll was light for such a severe earthquake, it was felt over a vast area and damage was widespread across the state.
Wild water caused most of the casualties and much of the damage. An open-ocean tsunami assaulted British Columbia, Washington State, Oregon and California, with damage recorded as far away as Hawaii and Japan. Terrifying local waves reached the awesome height of 70 m (230 ft) at Valdez, which subsequently had to be relocated to higher ground. There were landslides and fissuring that significantly realigned the landscape, and all Alaska’s major towns and cities were affected to some degree, though the fact that many buildings – especially houses – were constructed of wood ensured that property damage did not reach epic proportions. Anchorage, however, was hit hard. Many buildings and much of its infrastructure was destroyed and the village of Chenga in Prince William Sound vanished, along with the hamlets of Girdwood and Portage. Aftershocks were felt for 18 months.
When: March 27 1964
Where: Alaska, USA
Death toll: 131 (115 in Alaska and 16 in Oregon and California)
You should know: The great Alaska earthquake had a long reach. A series of seismic waves travelled round the world, with water rising and falling as far away as South Africa. There was also considerable aquatic disturbance nearer home, right down to Texas and Florida on the other side of the continental USA, where the effects were so intense in enclosed areas like harbors and marinas as far south as Louisiana that a number of boats were sunk.