March 27th marks the 50th anniversary of the most powerful earthquake ever recorded in North America. It had a moment magnitude of 9.2 and affected some 200,000 miles of Alaska real estate, permanently raising some areas by as much as 30 feet and lowering other regions by as much as 8 feet. The earthquake took 139 lives in sparsely populated Alaska. Most died from the associated tsunamis. The United States Geological Survey has marked the occasion with an informative short video, which deserves your attention:
The event itself occasioned well-earned shock and awe… and some learning from the experience. For example, Port Valdez, in Prince William Sound, suffered liquefaction, a major underwater landslide, and loss of 30 lives from the resulting tsunami. In post-disaster surveys, geologists learned that something like nine similar events had occurred over the previous 5000 years, and that future earthquakes could be expected. Port Valdez was deemed vulnerable to similar liquefaction and flood damage in coming years. With that thought firmly in hand, the entire town was rebuilt at a higher elevation.
But there are signs that we’re failing to take the experience sufficiently to heart. Some points worth noting:
The risk is global. Similar threats exist elsewhere around the world. Events of this magnitude occur somewhere on the Earth on average perhaps once a decade. Recall the Indonesian earthquake and tsunami of 2004 and the Great Tohoku earthquake and tsunami that crushed Fukushima in 2011. Here in the United States, a similar event in the Cascadia subduction zone off the Pacific Northwest draws one day nearer every day. There’s little sign in the land use and development along our Pacific coast that we are adequately factoring this risk into our planning and thinking.
Magnitude 9.2 doesn’t represent the limit. The 1960 Valdivia earthquake in Chile attained a moment magnitude of 9.5. Earthquake scenarios – perhaps corresponding to magnitudes approaching 10? – affecting larger areas appear possible. It’s likely we have no records of these solely because we’ve maintained records over a short geological span. Because the scale is logarithmic, a magnitude-10 event would represent some 30 times the energy release of a magnitude 9 event.
Loss of life and business disruption would be far greater at other sites. The suffering and damage in rural, small-town Alaska was bad enough. But an event hitting the corridor between Vancouver, Canada and San Francisco, California would be catastrophic. Picture casualties in the thousands, and losses in the $1T range.
This 50th-anniversary? Perhaps a good day to reflect on what it means to do life on a planet conducting its business through extreme events. Is your family ready? Your workplace? Your community?