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| 2014–2016 Cascadia tremor | |
|---|---|
| Name | 2014–2016 Cascadia tremor |
| Date | 2014–2016 |
| Location | Cascadia Subduction Zone, Pacific Northwest |
| Magnitude | episodic tremor and slip |
| Depth | shallow to mid-crustal |
| Type | slow slip event and non-volcanic tremor |
| Affected | British Columbia, Washington, Oregon, Northern California |
2014–2016 Cascadia tremor was a prolonged episode of episodic tremor and slip (ETS) within the Cascadia Subduction Zone beneath the Pacific Northwest that produced widespread non-volcanic tremor and slow slip from 2014 through 2016. The event attracted attention from institutions such as the United States Geological Survey, Natural Resources Canada, University of Washington, Oregon State University, and Simon Fraser University for its duration, spatial extent, and implications for megathrust earthquake hazard. Researchers from agencies including the Pacific Northwest Seismic Network, Canadian National Seismograph Network, Geological Survey of Canada, and the California Geological Survey used seismic, geodetic, and geodynamic tools to document tremor migration, slow slip, and strain accumulation.
The phenomenon occurred along the interface of the Juan de Fuca Plate and the North American Plate in the Juan de Fuca Ridge region adjacent to the Cascadia Subduction Zone, an area historically studied after paleoseismic investigations at Willapa Bay, Crescent City, California, Clayoquot Sound, and Cape Mendocino. Episodic tremor and slip was first characterized in the Nankai Trough context and later observed in the Pacific Northwest following deployments by groups associated with IRIS, USArray, British Columbia Ministry of Forests, and university observatories including Vancouver Island University. The 2014–2016 episode followed earlier ETS episodes documented in 2004, 2008, and 2010 that involved cooperation among National Science Foundation, Natural Environment Research Council, and provincial partners.
From late 2014 through 2016, seismic networks recorded bursts of non-volcanic tremor and slow slip that migrated along the margin between northern Vancouver Island and southern Oregon Coast Range, with notable activity near Tofino, British Columbia, Portland, Oregon, Seattle, Washington, Astoria, Oregon, and Newport, Oregon. Initial tremor onset was detected by the Pacific Northwest Seismic Network and corroborated by the Canadian Hazard Information Service, with episodes of intensified tremor in 2015 concurrent with elevated slow slip measured by continuous GPS stations operated by UNAVCO, Geoscience BC, and university networks. The sequence included episodic migration both northward and southward reminiscent of ETS episodes in Shikoku and the Kii Peninsula, and concluded in 2016 with diminished tremor rates but persistent geodetic adjustments.
Seismic records from broadband instruments operated by IRIS and regional arrays showed low-frequency, emergent signals characteristic of non-volcanic tremor similar to signals from the Nankai Trough, Taiwan ETS, and Mexico slow slip observations. Geodetic displacements on continuous GPS monuments indicated transient aseismic slip across patches of the megathrust with surface deformation patterns analyzed using methods developed at Scripps Institution of Oceanography, Caltech, and Massachusetts Institute of Technology. Tremor episodes were spatially correlated with areas of high pore-fluid pressure inferred from receiver function analyses by researchers at University of British Columbia and University of Victoria, and with fault zone properties modeled in studies at Stanford University and Purdue University.
Investigators interpreted the event as a manifestation of frictional heterogeneity and fluid-driven fault weakening along the locked-to-creeping transition of the Cascadia Subduction Zone megathrust, invoking concepts developed in laboratory studies at Los Alamos National Laboratory and Lawrence Livermore National Laboratory. Hypotheses included transient increases in pore-fluid pressure, rate-and-state frictional behavior, and dynamic triggering by teleseismic waves from distant events such as those recorded by Japan Meteorological Agency networks. Numerical simulations by groups at University of California, Berkeley, ETH Zurich, and University of Oxford reproduced migration patterns via slow rupture and fluid diffusion models.
The tremor sequence produced minimal direct damage but heightened concern among emergency agencies including the Federal Emergency Management Agency, British Columbia Emergency Management organizations, Washington Emergency Management Division, and municipal bodies in Vancouver, Victoria, Seattle, and Portland because ETS episodes can modulate stress on locked patches of the megathrust near population centers. Indirect impacts included increased public attention from media outlets such as the Vancouver Sun, Seattle Times, The Oregonian, and scientific briefings to legislative bodies in Ottawa, Sacramento, and Olympia, Washington. Tsunami hazard from the tremor itself was negligible, yet the association with megathrust behavior underscored preparedness initiatives by NOAA, PNSN, and coastal municipalities.
A coordinated response engaged institutions including USGS, Natural Resources Canada, National Oceanic and Atmospheric Administration, University of Washington, Oregon State University, Simon Fraser University, University of Victoria, and international collaborators from University of Tokyo and University of Auckland. Efforts expanded seismic station density via deployments by IRIS, UNAVCO, and the Pacific Northwest Seismic Network, and enhanced marine geodetic surveys by research vessels affiliated with Woods Hole Oceanographic Institution, Institute of Ocean Sciences, and University of Washington Oceanography. Data sharing through networks such as SCEC and international workshops facilitated rapid analysis by teams at Jet Propulsion Laboratory, NOAA Pacific Marine Environmental Laboratory, and Geological Survey of Canada.
The episode informed seismic hazard models used by USGS National Seismic Hazard Model, Geological Survey of Canada assessments, and regional resilience planning by agencies like Federal Emergency Management Agency and provincial emergency management offices. Findings influenced retrofit priorities in cities including Seattle, Portland, Vancouver, and Victoria and informed tsunami planning coordinated with NOAA National Weather Service and coastal municipalities. Continued research by centers such as Pacific Northwest Seismic Network, Scripps Institution of Oceanography, and university consortia aims to refine the relationship between ETS and megathrust rupture to improve probabilistic forecasts used by policymakers in Olympia, Washington, Sacramento, California, and Victoria, British Columbia.
Category:Earthquakes in the Pacific Northwest Category:Cascadia Subduction Zone