50th Anniversary of the Great M9.2 Alaska Earthquake of March 27, 1964
March 27, 2014 marks the 50th anniversary of the great Alaska earthquake. On March 27, 1964 at 5:36 pm local time a magnitude 9.2 earthquake began, ultimately breaking a fault about 400 miles long and a few 100 miles wide, rupturing from beyond the western edge of Kodiak Island to the eastern side of Prince William Sound and from well offshore inland to Upper Cook Inlet. The earthquake lasted approximately 4.5 minutes and is the largest earthquake in U.S. history and the second largest globally, next to the great 1960 M9.5 Chile earthquake. The earthquake was felt in Dutch Harbor, 800 miles west of Anchorage, and in Seattle 1200 miles to the southeast of Anchorage. Water well levels rose and fell in 47 states of the U.S.
Middleton Island, Alaska. This rock platform was uplifted about 11 feet in tens of seconds by the 1964 Alaska earthquake. White specks are seagulls. Photo was taken near 7-foot tide stage on April 4, 1964. Figure 36, U.S. Geological Survey Professional paper 543-I; Figure 4-A, Circular 491.
As more recent great subduction zone earthquakes have demonstrated, the vast majority of the fatalities were caused by locally generated tsunamis; only 9 of the 129 fatalities attributed to the 1964 Alaska earthquake were caused directly by strong ground shaking. Property losses totaled $2.3 Billion in 2014 dollars. Key practical scientific lessons were learned from the 1964 Alaska earthquake: 1) widespread liquefaction brought about the development of modern methods for assessing liquefaction hazard, 2) the potential for activation of large-scale secondary faulting became clear, and 3) the first direct evidence for how far-traveled tsunamis are generated led to a basic understanding of tectonic tsunami generation and inundation mapping around the globe.
The rails near the head of Turnagain Arm outside Anchorage were torn from their ties and buckled during the 1964 earthquake. Figure 24, U.S. Geological Survey Professional paper 541.
In the 50 years since 1964 economies and social structures from widespread States and countries have become much more intertwined, so a repeat of the great 1964 Alaska earthquake will likely have greater impacts on the Pacific Northwest and elsewhere. The greatest far-flung impacts from the 1964 earthquake along west coast of North America were due to its tsunami waves. In British Columbia communities along the southwest coast of Vancouver Island were hit hardest, with 21-foot waves damaging and flooding the cities of Alberni and Port Alberni. Along the Washington coast, 5- to 6-foot tsunami waves struck Ocean City and collapsed the bridge over Copalis River. Wave heights at Moclips, Sea View, La Push and Wreck Creek reached an estimated 11, 12, 5, 7, and 15 feet, respectively. In Oregon the tsunami took four lives. Seaside, struck by a 10-foot wave, was the hardest hit. Tsunami wave heights reached 10 to 11.5 feet at Depoe Bay, Newport, Florence, Reedsport, Brookings, and 14 feet at Coos Bay. Four people died at Beverly Beach State Park. California lost 12 people to the tsunami. 10 of these fatalities occurred in inundation-prone Crescent City, which was struck by an unusually large 21-foot wave owing to the shape of the ocean bottom just offshore. Cities all the way to San Diego experienced significant tsunami waves, with one fatality in Los Angeles occurring when the 6-foot tsunami surge struck the Cerritos Channel.
Many institutions are commemorating the 1964 Alaska earthquake by taking stock of preparations and practicing future earthquakes. The State of Alaska is conducting the Alaska Shield Exercise, which simulates the ground shaking and tsunami effects that occurred during the 1964 earthquake and exercises today’s response plans capabilities. The Alaska Shield scenario is the centerpiece of the FEMA National Exercise Program Capstone Exercise for 2014, which has participants from across the U.S.
For lots more information check out http://earthquake.usgs.gov/earthquakes/events/alaska1964/. Additional information includes 1964 Alaska Earthquake Fact Sheet and a Online Resources Handout