ResilienceCascadia initiative gathers information on Northwest Pacific seismic risks

Early data coming in from a massive, four-year deployment of seismometers onshore and offshore in the Pacific Northwest are giving scientists a clearer picture of the Cascadia subduction zone, a region with a past and potential future of devastating “megathrust” earthquakes.

The preliminary results from the Cascadia Initiative include a report of previously undetected, small earthquakes offshore, and seismic imaging that reveals new offshore structures at the subduction zone. The reports, to be published as a focus section in the September-October 2015 issue of Seismological Research Letters (SRL), also provide an update on how well the Initiative’s instruments are operating, including a look at how seafloor pressure monitors can detect tsunamis in the region.

The Cascadia subduction zone (CSZ) is a 680-mile Pacific fault that runs roughly from Cape Mendocino, California in the south to northern Vancouver Island, British Columbia. The zone marks the place where the Juan de Fuca and Gorda tectonic plates slip beneath the North American plate at a rate of about 2.3 to 4 centimeters (.9 to 1.6 inches) per year. At subduction zones like this throughout the globe, the tremendous strain built up in these crustal collisions has been released in the world’s largest recorded earthquakes. These megathrust quakes include the 2004 magnitude 9.1 Sumatran Andaman earthquake that devastated parts of Indonesia, and the 2011 magnitude 9.0 Tohoku earthquake in Japan.

Although the CSZ has been relatively quiet in recent years, researchers have compiled a historical record of full and partial ruptures of the massive fault, with a magnitude 9.0 earthquake and tsunami last occurring in 1700. Scientists estimate that these megathrust quakes occur at 400 to 600-year intervals. Agencies such as the U.S. Federal Emergency Management Agency (FEMA) and others have warned of catastrophic damage along the U.S. Northwest coast in the wake of a megathrust quake.

The Seismological Society of America (SSA) notes that the Cascadia Initiative, funded from 2011 to 2015 by the National Science Foundation, was designed in part to collect information on the potential seismic threat of the CSZ. The project includes twenty-seven new inland seismic stations, upgrades to 232 other land stations, and the deployment of sixty new seismometers on the ocean bottom, spread across the tectonic plates. The data collected by the initiative is openly available to the full scientific community in a database managed by the Incorporated Research Institutions for Seismology (IRIS) Data Management Center.