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REPORT

Great Cascadia Earthquake Tricentennial

Seaside, Oregon
4–8 June 2000

Conveners:

John J. Clague
Dept. of Earth Sciences, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada, and Geological Survey of Canada, 101-605 Robson St., Vancouver, BC V6B 5J3, Canada
Brian F. Atwater
U.S. Geological Survey at Dept. of Geological Sciences AJ-20, University of Washington, Seattle, WA 98195
Kelin Wang
Pacific Geoscience Centre, Geological Survey of Canada, 9860 West Saanich Road, Sidney, BC V8L 4B2, Canada
Yumei Wang
Oregon Department of Geology and Mineral Industries, 800 NE Oregon St., No. 28, Portland, OR 97232
Ivan G. Wong
URS Greiner Woodward Clyde Federal Services, 500 12th St., Ste. 200, Oakland, CA 94607


Cosponsored by:
• U.S. Geological Survey, Geological Survey of Canada, and
• Oregon Department of Geology and Mineral Industries



The year 2000 marks the tricentennial of the last great (magnitude 8 or larger) earthquake at the Cascadia subduction zone, which is located along the Pacific coast of North America from British Columbia to northern California. Coastal and offshore work has confirmed that many great plate-boundary earthquakes have struck this region in the Holocene, and geodetic studies have shown that the subduction zone is accumulating strain that will be released in a future earthquake.

To commemorate the tricentennial, almost 100 geologists, geophysicists, engineers, and public officials gathered in Seaside, Oregon, in the first week of June 2000 to critically review current knowledge about great Cascadia earthquakes, clarify the hazards posed by these earthquakes, discuss appropriate strategies for reducing earthquake losses, and identify priority research directions. Further understanding of the great earthquake potential of the Cascadia subduction zone is required for seismic hazard characterization, engineering design, emergency planning and response, and other mitigation efforts in a region with a population of nearly 10 million people. Seaside was an appropriate place to hold the conference because much of the community, including the conference hotel, lies within the inundation zone of the tsunami of the 1700 earthquake!

The conference consisted of three days of indoor sessions, a field trip, and a public forum on Cascadia earthquakes and tsunamis. Sessions on the first day dealt with earthquake hazards and their mitigation. These initial sessions provided focus for subsequent sessions on regional earthquake histories, tectonics, and present-day seismicity and strain accumulation. Evidence for past Cascadia earthquakes was examined and discussed during a canoe trip along the Niawiakum River in southwestern Washington and at a nearby park where lake, tidal marsh, and deep-sea cores collected during previous paleoseismological investigations were displayed. The public forum, held on the first evening of the conference, attracted more than 200 people, including two state senators, and allowed conference participants to hear concerns of local residents. The forum and the conference as a whole were covered extensively in local newspapers.

A huge amount of progress has been made in understanding the behavior of the Cascadia subduction zone over the past two decades. Fifteen years ago, scientists were debating whether great earthquakes occur at the subduction zone. Today, few scientists doubt that great earthquakes occur in this region; rather, the discussion has shifted to questions such as the magnitude of the earthquakes and attendant tsunamis, the location and width of the seismogenic zone, and the involvement of crustal structures in plate-boundary rupture. These issues were topics of discussion and debate at the conference. Consensus was achieved on several important issues; major points of consensus are summarized below.

Additional Reading

Atwater, B.F., and Hemphill-Haley, E., 1997, Recurrence intervals for great earthquakes of the past 3500 years at northeastern Willapa Bay, Washington: U.S. Geological Survey Professional Paper 1576, 108 p.

Clague, J.J., 1997, Evidence for large earthquakes at the Cascadia subduction zone: Reviews of Geophysics, v. 35, p. 439–460.

Flück, P., Hyndman, R.D., and Wang, K., 1997, Three-dimensional dislocation model for great earthquakes of the Cascadia subduction zone: Journal of Geophysical Research, v. 102, p. 20,539–20,550.

Hyndman, R.D., and Wang, K., 1995, The rupture zone of Cascadia great earthquakes from current deformation and the thermal regime: Journal of Geophysical Research, v. 100, p. 22,133–22,154.

McNeill, L.C., Goldfinger, C., Yeats, R.S., and Kulm, L.D., 1998, The effects of upper plate deformation on records of prehistoric Cascadia subduction zone earthquakes, in Stewart, I., and Vita-Finzi, C., eds., Coastal tectonics: Geological Society of London Special Publication 146, p. 321–342.

Myers, E., Baptista, A.M., and Priest, G.R., 1999, Finite element modeling of potential Cascadia subduction zone tsunamis: Science of Tsunami Hazards, v. 17, p. 3–18.

Wang, Y., and Clark, J.L., 1999, Earthquake damage in Oregon, preliminary estimates of future earthquake losses: Oregon Department of Geology and Mineral Industries Special Paper 29, 59 p.

Conference Participants

Kenneth R. Aalto
Hans Abramson
John Adams
Jim Ament
Brian F. Atwater
Alfred A. Aya Jr.
Donald Ballantyne
Walter Barnhardt
John D. Beaulieu
James Bela
Thomas M. Brocher
Kevin M. Brown
Kenneth W. Campbell
Gary Carver
Marcos Cistemas
John J. Clague
George L. Crawford
Mark Darienzo
Lori Dengler
Herb Dragert
William M. Elliott
Brooke K. Fiedorowicz
Paul Flück
Carrie E. Garrison-Laney
Jan Glarum
David Gronbeck-Jones
Sean S.P. Gulick
Michael R. Hagerty
Tsuyoshi Haraguchi
Eileen Hemphill-Haley
Mark Hemphill-Haley
Jon Hofmeister
Tom Horning

Jonathan F. Hughes
Ian Hutchinson
Roy Hyndman
Thomas S. James
Ike Jensen
Joel E. Johnson
Robert Kayen
Harvey Kelsey
Steven Kramer
Roland LaForge
Robert Losey
Ian Madin
Ravindra K. Mahajan
Brian G. McAdoo
Pat McCrory
David McDaniel
Lisa McNeill
Dorothy Merritts
Edward Meyers
Meghan Miller
Ray Miller
Patrick Monahan
Takashi Nakata
Alan R. Nelson
Hans Nelson
Linda Noson
Dennis Olmstead
Simon M. Peacock
David M. Perkins
Curt D. Peterson
George Plafker
George R. Priest
Patrick Pringle

Tim Richter
James Roddey
Garry C. Rogers
Larry Ruff
Takeshi Sagiya
Kenji Satake
Yuki Sawai
Robert Schlichting
Ian Shennan
Brian Sherrod
Nobuo Shuto
John D. Sims
Irene Thomas
C.R.H. Thoms
Christopher Thompson
Robert M. Thorson
Christopher Tucker
Martitia P. Tuttle
Maillian Uphaus
Bev Vogt
Timothy J. Walsh
Kelin Wang
Yumei Wang
Zhenming Wang
Ray Wells
William S.D. Wilcock
Donald S. Windeler Jr.
Robert Witter
Ivan Wong
Robert Yeats
Robert Youngs