The U.S. Oregon and Washington states, and the Canadian province of British Columbia form part of the geologically active continental margin of North America. This region--often referred to as central-northern Cascadia or the Pacific Northwest (PNW)--includes large-scale tectonic and volcanic features including the subducting Gorda/Juan de Fuca/Explorer oceanic plate system, the Cascadia accretionary margin and forearc, and the Cascade Volcanos. These features represent major geohazards for the local populations and infrastructure of this region.

At the Cascadia Subduction Zone, the ongoing descent of the Juan de Fuca plate system beneath the northwestern coast of North America has generated large earthquakes and associated tsunamis in the past. The last great earthquake at Cascadia occurred on January 26, 1700 AD and is estimated to have been a magnitude 9, similar to the devastating 2011 earthquake in Japan. Studies of the history of earthquakes along the margin indicate they occur every 300 to 550 years at Cascadia and scientists estimate an ~14% chance that the next great earthquake will happen in the coming 50 years. The subduction zone at present is eerily quiet with little seismicity detected within the Oregon to Washington portion. Scientists believe this lack of seismicity reflects the “locked” state of the megathrust at present and that stress is currently quietly accumulating as the Juan de Fuca plate system steadily descends beneath North America. With the paucity of recorded seismicity, little is known of the properties of the subduction zone fault interface (i.e., depth, roughness, thickness, and acoustic impedance, among others) within the mega-thrust earthquake zone and how they vary along and across the Oregon to British Columbia margin.  The current observations allow for a wide range of possible future earthquake and tsunami scenarios. Comprehensive characterization of this zone is needed to quantify earthquake and tsunami hazards within the region.

This summer scientists from a number of U.S. and Canadian academic and federal institutions are conducting 3 related geophysical investigations to provide the observations and data necessary to address fundamental science questions relevant for understanding the structures and processes that contribute to, and result from, earthquakes, tsunami, and associated geohazards in the PNW. The studies include use of marine multi-channel seismic imaging techniques and deployment of ocean-bottom instrumentation to record seismic waves from marine acoustic pulses, using the  R/V Marcus G. Langseth, the R/V Oceanus, and ocean bottom seismic instrumentation from the US Ocean Bottom Seismometer Instrument Pool (OBSIP).  A large array of land seismometers in Oregon and southern Washington has been deployed to  record seismic waves from Langseth's marine sources as well as natural seismicity.