Cascadia Subduction Zone Earthquake Scenario Project

CREW (Cascadia Region Earthquake Workgroup) is the only organization that focuses its attention on the entire Cascadia region. This region crosses three states and one international boundary. As a private/public, non-profit organization, CREW can initiate interactions across jurisdictions and compile region-wide information of importance to both the public and private sector.

A scenario describing the likely scope and nature of the effects of a future Cascadia Subduction Zone earthquake is essential to the development of effective multi-state and international earthquake risk reduction strategies. The occurrence of recent subduction zone earthquakes elsewhere provide insight into the likely severity, kinds of impact, and complexities of managing wide-scale, regional disasters. However, differences in population density, building codes, land use planning, cultures, and commercial infrastructure make the lessons learned in these earthquakes only partially transferable to the Pacific Northwest and southwestern British Columbia.

A Cascadia Subduction Zone earthquake scenario will portray the unique characteristics and serious consequences of a Cascadia Subduction Zone earthquake on the people and business that reside in the region. This better understanding will provide a basis for multi-state and international earthquake risk-reduction strategies. A Cascadia Subduction Zone earthquake scenario will illustrate private sector dependencies on the continued functioning of public sector infrastructure, such as transportation networks, to carry out their own response and recovery actions.

The Cascadia Subduction Zone earthquake scenario provides a framework into which CREW, or others, can integrate more detailed, but spatially limited scenario efforts. Over time, the continued addition of detailed inventory and scientific data to the Cascadia scenario framework will provide an increasingly clearer portrait of vulnerabilities and potential economic impact which could occur from central British Columbia, Canada to northern California. CREW's Cascadia Subduction Zone scenario will provide a comprehensive tool for compiling data collected by many different sources in different locations of the Cascadia region.

Background Information
The Cascadia Subduction Zone is the major fault zone that extends offshore parallel to the Pacific coast from central Vancouver Island, Canada south to northwestern California. Geologic evidence, primarily well-documented elevation changes in coastal marshes, is interpreted as indicating the repeated occurrence of great earthquakes along this zone. These great quakes generate water waves, called tsunamis, capable of causing damage to coastal areas on both sides of the Pacific. Using detailed tsunamis records from Japan, geologists have been able to date the last Cascadia earthquake as occurring on January 26, 1700. On the Oregon coast, a preserved native American fire pit covered with tsunami deposits inplaced at the same time the marshy site subsided, shows that Pacific coast residents were clearly affected by this earthquake. The geologic record indicates intervals between these great earthquakes of 500 to 600 years.

The Cause for Concern about Cascadia Earthquakes
In less than 50 years, a number of great Cascadia-like earthquakes have occurred around the Pacific Rim, including Chile (1960), Alaska, (1964) and Mexico (1985). A unique aspect of a great Cascadia earthquake is the strong likelihood that the three greater metropolitan areas of Portland, Seattle, and Vancouver will simultaneously feel the effects of strong and sustained ground shaking. This wide-spread ground shaking combined with accompanying elevation changes and the likely generation of a tsunami along the Pacific coast, will cause loss of life, property damage, and business interruption in vulnerable locations through out southwestern British Columbia, Washington, Oregon, and northwestern California. The broad geographic distribution of damaging impacts will generate special challenges and severely stress the response and recovery resources of the three Pacific states and British Columbia.

The regional exposure of people and property to earthquake hazards in the Pacific Northwest and southwestern British Columbia has continued to expand over the past century. In just the period of 1980 to 1990, the population in the state of Washington increased by nearly 20% (US Census). This increased exposure is reflected in dense urbanization along the I5 corridor and in southwestern British Columbia, the development of forestry and fishery industries along the coast, and the continued expansion of Pacific Rim trade involving Ports like Vancouver, Seattle, Tacoma, and Portland.

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