Tenth Anniversary of the Magnitude 9.2 Indian Ocean Earthquake and Tsunami

The day after Christmas will mark the tenth anniversary of the Magnitude 9.2 Indian Ocean earthquake that produced the single-most devastating tsunami in recorded history, killing more than 230,000 people throughout the countries along the Indian Ocean and leaving more than 1.7 million people homeless. The rupture of this megathrust earthquake initiated off the west coast of Sumatra along the Sunda trench subduction zone.

This devastation served as a strong reminder that Washington State is also vulnerable to this type of event. Tsunami deposits, drowned shorelines, and buried trees from the 1700 A.D. Magnitude 8.8–9.2 megathrust earthquake along the Cascadia subduction zone have been located in numerous places along the Washington, Oregon, California, and Vancouver Island coast. The 2004 Indian Ocean earthquake resulted in the Tsunami Warning and Education Act of 2006, wherein NOAA formalized and expanded the National Tsunami Hazard Mitigation Program, a partnership with Pacific states to protect the west coast from tsunamis.

To better prepare coastal communities for future earthquake-generated tsunamis, hazards geologists with the Division, the National Center for Tsunami Research at NOAA’s Pacific Marine Environmental Laboratory, and scientists with the University of Washington model tsunami inundation in population centers both along the Washington coast and within the Puget Sound. To do this complex math, they use software (Clawpack), developed by geeks at the Applied Mathematics Department of UW or the MOST model, developed by NOAA. The Division recently published tsunami inundation modeling for the Everett area, and is currently focusing efforts on the San Juan Islands.

Inundation modeling tells us where we are most vulnerable and helps guide innovative evacuation strategies for at-risk communities. In Westport, where evacuation is especially difficult, demolition has already begun on the Ocosta Elementary School (see photo below), and a vertical tsunami evacuation structure will soon be built in its place. The 28-ft-tall evacuation structure sits 55 ft above sea level, can hold over 1,000 people, and was designed to withstand a Magnitude 9 near-field earthquake. It was designed by Degenkolb Engineers and TCF Architecture, through the efforts of Project Safe Haven, which was launched by the Washington State Emergency Management Division in 2011.

Ocosta School elementary kids gleefully watching their school being demolished.
Ocosta School elementary kids gleefully watching their school being demolished.

Thanks to continuing efforts, a tsunami berm is also proposed adjacent to the Long Beach Elementary School. The landscaped berm would replace an existing bleacher there, and would hold about 800 people atop it during an emergency, while serving as an attractive amenity every day.

The Division documents tsunami-related news in our bi-monthly newsletter, TsuInfo.