March 27th Marks the 50th Anniversary of the Great M9.2 Alaska Earthquake

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.

Picture2Middleton 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.

Picture1The 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

February 28 Marks the Anniversary of the M6.8 Nisqually Earthquake

February 28th marks the anniversary of the Nisqually Earthquake. The earthquake had a magnitude of 6.8, a depth of 52 km, with a hypocenter about 17.8 km NE of Olympia, Washington.  A clearinghouse with information about this earthquake can be found here.

314 Year Anniversary of the Great 1700 Cascadia Subduction Zone Earthquake

January 26, 2014 marked the 314-Year Anniversary of the last Cascadia Earthquake

SEATTLE— The last Cascadia Subduction Zone earthquake occurred one hundred years before Lewis and Clark saw the Pacific Ocean. It was a time when native traditions spoke of the ground shaking and the waters rising. There were no bridges to fall and no schools, hospitals and other critical infrastructure in tsunami inundation zones. It was a time when Cascadia was much more resilient than today. “The very advances that are the foundations of our modern communities create vulnerability along with convenience” said Michael Kubler, Cascadia Region Earthquake Workgroup (CREW) President. “The revised Cascadia scenario is a crucial tool for regional leaders to use in developing policies and plans for the next earthquake.”

Events over the last few years have expanded our understanding of earthquake science and the hazards faced by our region from a future Cascadia Subduction Zone earthquake. The Cascadia Subduction Zone extends along the coastlines of northern California, Oregon, Washington, and southern British Columbia. There’s no doubt that Cascadia is capable of producing earthquakes and tsunamis on the same scale as the magnitude 8.8 earthquake off Chile in 2010 and the magnitude 9.0 quake that devastated the east coast of Japan in 2011.

Cascadia’s last great earthquake occurred on January 26, 1700—stresses have been building on the fault ever since. While the full extent of the earthquake hazard was not realized until the 1980s, the Cascadia subduction zone is now one of the most closely studied and monitored regions in the world. “In 2005 CREW first published the Cascadia earthquake scenario, but so much new information has emerged that an update was needed” said Heidi Kandathil, CREW Executive Director. The newly updated Cascadia Scenario joins the list of other free products developed by CREW to help the region’s residents, schools, businesses, planners, and emergency managers prepare for future earthquakes. The Scenario and other materials are available online at http://tinyurl.com/m34v2ex.

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For more about CREW and the new Cascadia Subduction Zone Scenario, seeCascadia Factsheet.

Insurance Bureau of Canada reports on potential earthquake impacts

A new scientific study on the impact of a major earthquake in Canada, released in Ottawa on October 29th, 2013, by Insurance Bureau of Canada (IBC), leaves no doubt that Canada is not prepared to handle a major earthquake, which could happen at any time, and that the economic impact would be significant. IBC commissioned the study by AIR Worldwide, global experts in catastrophe modeling. The study is a peer-reviewed analysis of the impact of two major seismic events: one in British Columbia (western scenario) and the other in the Quebec City-Montreal-Ottawa corridor (eastern scenario).

Evacuation potential in SW Washington communities from Cascadia tsunami hazards

A new article in the journal Natural Hazards documents variations in population exposure in coastal communities of Pacific and Grays Harbor counties to Cascadia-related tsunami hazards as a function of modeled pedestrian travel time to safety. Results suggest that successful evacuations may be possible in some communities assuming slow walking speeds, are plausible in others if travel speeds are increased, and are unlikely in another set of communities given the large distances and short time horizon. Communities can use these results to help prioritize tsunami risk-reduction efforts, such as education and training in areas where evacuations are plausible and vertical-evacuation strategies in areas where they currently are not.

More information can be found at http://www.springerlink.com/content/a6177520x5k6080t/ or by emailing the lead author at nwood@usgs.gov.