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Slow-slip phenomena in Cascadia from 2007 and beyond; a review

Joan Gomberg, Paul Bedrosian, Paul Bodin, Michael Bostock, Michael Brudzinski, Ken Creager, Herb Dragert, Gary Egbert, Abhijit Ghosh, Joe Henton, Heidi Houston, Honn Kao, Pat McCrory, Tim Melbourne, Simon Peacock, Evelyn Roeloffs, Justin Rubinstein, David Schmidt, Anne Trehu, John Vidale, Kelin Wang and Aaron Wech
Slow-slip phenomena in Cascadia from 2007 and beyond; a review
Geological Society of America Bulletin (July 2010) 122 (7-8): 963-978


Recent technological advances combined with more detailed analyses of seismologic and geodetic observations have fundamentally changed our understanding of the ways in which tectonic stresses arising from plate motions are accommodated by slip on faults. The traditional view that relative plate motions are accommodated by a simple cycle of stress accumulation and release on "locked" plate-boundary faults has been revolutionized by the serendipitous discovery and recognition of the significance of slow-slip phenomena, mostly in the deeper reaches of subduction zones. The Cascadia subduction zone, located in the Pacific Northwest of the conterminous United States and adjacent Canada, is an archetype of exploration and learning about slow-slip phenomena. These phenomena are manifest as geodetically observed aseismic transient deformations accompanied by a previously unrecognized class of seismic signals. Although secondary failure processes may be involved in generating the seismic signals, the primary origins of both aseismic and seismic phenomena appear to be episodic fault slip, probably facilitated by fluids, on a plate interface that is critically stressed or weakened. In Cascadia, this transient slip evolves more slowly and over more prolonged durations relative to the slip in earthquakes, and it occurs between the 30- and 40-km-depth contours of the plate interface where information was previously elusive. Although there is some underlying organization that relaxes nearly all the accrued plate-motion stresses along the entirety of Cascadia, we now infer that slow slip evolves in complex patterns indicative of propagating stress fronts. Our new understanding provides key constraints not only on the region where the slow slip originates, but also on the probable characteristics of future megathrust earthquakes in Cascadia. Herein, we review the most significant scientific issues and progress related to understanding slow-slip phenomena in Cascadia and highlight some of their societal implications. We provide a comprehensive review, from the big picture as inferred from studies of regional-scale monitoring data to the details revealed by innovative, focused experiments and new instrumentation. We focus on what has been learned largely since 2007, when several major investments in monitoring and temporary deployments dramatically increased the quality and quantity of available data.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 122
Serial Issue: 7-8
Title: Slow-slip phenomena in Cascadia from 2007 and beyond; a review
Affiliation: U. S. Geological Survey, Seattle, WA, United States
Affiliation: Cascadia 2007 and Beyond Working GroupInternational
Pages: 963-978
Published: 201007
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 108
Accession Number: 2010-050179
Categories: Solid-earth geophysicsStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., sketch maps
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201027
Program Name: USGSOPNon-USGS publications with USGS authors
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