Cascadia Initiative

Cascadia Initiative. The Cascadia Initiative was a large-scale, multi-institutional amphibious geophysical experiment focused on the Cascadia subduction zone. Running from 2011 to 2015, it represented an unprecedented effort to instrument both the offshore and onshore regions of this seismically active margin. The primary goal was to better understand megathrust earthquake and tsunami hazards by studying the structure and behavior of the Juan de Fuca Plate as it subducts beneath the North American Plate. The project was funded primarily by the National Science Foundation and constituted a flagship effort within the broader EarthScope program.

Background and objectives

The initiative was motivated by the significant seismic hazard posed by the Cascadia subduction zone, which is capable of generating magnitude 9.0 megathrust earthquakes similar to the 2004 Indian Ocean earthquake and tsunami and the 2011 Tōhoku earthquake and tsunami. Historical and geological evidence, including studies of coastal tsunami deposits and dendrochronology, indicated the last great earthquake occurred in January 1700. Key scientific objectives included imaging the subduction interface to understand locking and slip behavior, characterizing the structure of the Juan de Fuca Plate and overlying North American Plate, and monitoring seismicity and slow slip events across the entire plate boundary system. The project aimed to fill critical data gaps, particularly in the offshore environment where conventional land-based networks were blind.

Scientific instrumentation and deployment

The experiment's core was a dense array of ocean-bottom seismometers (OBS) deployed across the continental shelf, slope, and deep ocean of the Pacific Ocean. These instruments, provided by the Ocean Bottom Seismograph Instrument Pool (OBSIP), were complemented by a major expansion of onshore seismic stations from the Transportable Array component of EarthScope. Additional data streams included continuous Global Positioning System (GPS) measurements from both existing networks and new seafloor installations, as well as absolute pressure gauges. Deployments utilized multiple research vessels, including the R/V Atlantis and the R/V Thompson, with instruments serviced annually. This amphibious design created an integrated observing system spanning from the Gorda Ridge to Vancouver Island.

Key findings and scientific contributions

Data analysis revealed complex patterns of tectonic deformation, including detailed mapping of episodic tremor and slip (ETS) events along the subduction interface. Seismic imaging illuminated the geometry of the subducting slab, including potential zones of high fluid pressure that influence earthquake nucleation. Studies characterized abundant small-magnitude seismicity within the subducting Juan de Fuca Plate, providing insights into plate bending and hydration. The initiative also provided critical baseline data for assessing tsunami generation potential by constraining the shallow megathrust's locking state. Findings have been published in leading journals like Science and Nature, significantly advancing the field of subduction zone science and directly informing hazard assessments by the United States Geological Survey and Natural Resources Canada.

Operational challenges and logistics

Operating a major observatory on the seafloor presented formidable challenges, including extreme pressures, corrosive saltwater, and biological fouling of instruments. Recovery and redeployment cycles were constrained by harsh weather windows in the North Pacific Ocean. The high cost and technical complexity of offshore operations required meticulous planning by engineers from the Scripps Institution of Oceanography, the University of Washington, and Oregon State University. Data retrieval and management from hundreds of autonomous instruments created a substantial computational and archival burden, handled in part by the Incorporated Research Institutions for Seismology (IRIS) Data Management Center. Despite these hurdles, the project achieved an exceptionally high instrument recovery rate.

Collaboration and institutional involvement

The initiative was a model of broad scientific collaboration, led by a consortium of principal investigators from institutions like the University of California, San Diego, the University of Oregon, and the University of Texas at Austin. The National Science Foundation provided major funding through its Division of Ocean Sciences and Division of Earth Sciences. Essential infrastructure and support came from the Ocean Observatories Initiative, the U.S. Geological Survey, and Geological Survey of Canada. Data was made freely available to the global research community, fostering interdisciplinary studies in seismology, geodesy, marine geology, and physical oceanography. The project trained a generation of early-career scientists and engineers in amphibious geophysical research.