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Cascadia Subduction Zone Earthquake Scenario

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CCaassccaaddiiaa SSuubbdduuccttiioonn ZZoonnee EEaarrtthhqquuaakkeess:: AA MMaaggnniittuuddee 99..00 EEaarrtthhqquuaakkee SScceennaarriioo Update, 2013 Cascadia Region Earthquake Workgroup Also available as Washington Division of Geology and Earth Resources Information Circular 116, Oregon Department of Geology and Mineral Industries Open-File Report 0-13-22, and British Columbia Geological Survey Information Circular 2013-3 Cascadia Region Earthquake Workgroup (CREW) CREW is a non-profit coalition of business people, emergency managers, scientists, engineers, civic leaders, and government officials who are working together to reduce the effects of earthquakes in the Pacific Northwest. Executive Board President: John Schelling, Washington Emergency Management Division Vice President: Michael Kubler, Emergency Management, Providence Health & Services, Portland, OR Past President: Cale Ash, Degenkolb Engineers Secretary: Teron Moore, Emergency Management, British Columbia Treasurer: Timothy Walsh, State of Washington Department of Natural Resources Executive Director: Heidi Kandathil Board of Directors Steven Bibby, Security and Emergency Services, BC Housing Josh Bruce, Oregon Partnership for Disaster Resilience Kathryn Forge, Public Safety Canada Jere High, Oregon State Public Health Division Andre LeDuc, University of Oregon Charlie Macaulay, Global Risk Consultants Ines Pearce, Pearce Global Partners Althea Rizzo, Oregon Emergency Management Bill Steele, University of Washington, Pacific Northwest Seismic Network Yumei Wang, Oregon Department of Geology and Mineral Industries Supporting members Tamra Biasco, FEMA, Region X Craig Weaver, U.S. Geological Survey Joan Gomberg, U.S. Geological Survey Nate Wood, U.S. Geological Survey Acknowledgments CREW would like to thank Tamra Biasco and Joan Gomberg for overseeing the development of this updated edition of Cascadia Subduction Zone Earthquakes: A Magnitude 9.0 Earthquake Scenario. We would also like to thank everyone who shared information and materials or contributed their time and expertise to this project. CREW extends special thanks to Tim Walsh for his many contributions to the project’s final stages of review and development. Support for this publication was provided by FEMA, Department of Homeland Security, under the National Earthquake Hazard Reduction Program (NEHRP) State Cooperative Agreements. Points of view or opinions expressed in this document are those of the authors and do not necessarily represent the official position or policies of FEMA or the U.S. Department of Homeland Security. Writing and editing support was provided by Dr. Kyra L. Nourse. Approved by the CREW Board of Directors on September 6, 2013. Cascadia Subduction Zone Earthquakes: A Magnitude 9.0 Earthquake Scenario Update, 2013 Cascadia Region Earthquake Workgroup CONTENTS One Day in Cascadia ................................................................................................................................................ 1 Discovering Our Region’s Earthquake Profile ......................................................................................................... 2 Tectonic Collision Zone ........................................................................................................................................................ 2 On the Trail of the Biggest Quake of All .............................................................................................................................. 4 Anatomy of a Cascadia Subduction Zone Earthquake ............................................................................................ 5 The Locked Zone Breaks ...................................................................................................................................................... 5 The Earthquake Hits ............................................................................................................................................................ 6 A Tsunami is Born ................................................................................................................................................................ 7 What Are the Odds? ............................................................................................................................................................ 8 Predicting the Effects of The Next Big Earthquake ................................................................................................. 8 If the Earthquake Happens Tomorrow.... ............................................................................................................................ 8 How Will Essential Infrastructure Perform? ...................................................................................................................... 10 What Will Happen to Buildings? ........................................................................................................................................ 13 What Will Happen to Communities on the Coast? ............................................................................................................ 15 Earthquake and Tsunami Refugees ................................................................................................................................... 16 Other Far-Reaching Impacts of a Cascadia Earthquake and Tsunami ............................................................................... 17 Preparing for the Big One...................................................................................................................................... 18 Risk Assessment ................................................................................................................................................................ 18 Raising Awareness ............................................................................................................................................................. 19 Resilience Planning and Mitigation Strategies .................................................................................................................. 19 Engineering for Earthquakes ............................................................................................................................................. 20 Earthquake Early Warning Systems ................................................................................................................................... 21 Preparing for Tsunamis ..................................................................................................................................................... 21 Living in Cascadia .................................................................................................................................................. 23 Next Steps Forward ........................................................................................................................................................... 23 THE CASCADIA SUBDUCTION ZONE: The geography of northern California, Oregon, Washington, and southern British Columbia is shaped by the Cascadia subduction zone, where the North American Plate collides with a number of smaller plates: the largest of these is the Juan de Fuca Plate, flanked by the Explorer Plate to the north and the Gorda plate to the south. These smaller plates “subduct” (descend) beneath the North American Plate as they converge along a 700-mile long (1,130 km) boundary. A large portion of the boundary between the subducting and overriding plates resists the convergent motion, until this part of the boundary breaks in a great earthquake. Above: Schematic view of the source area for the largest Cascadia earthquakes. (Image adapted from U.S. Geological Survey Professional Paper 1707 (page 8), Atwater et al., http://pubs.usgs.gov/pp/pp1707/) ONE DAY IN CASCADIA Photo by Writegeist Photo by It’s 8:16 on a chilly, wet morning in early spring. You’ve just arrived at work and are pouring a cup of coffee when you become aware of a low rumbling noise. Within seconds, the rumbling becomes a roar, the floor beneath you heaves, and the building begins to pitch and shake so violently that you’re thrown to the floor. The roaring is joined by a cacophony of crashing as windows shatter and every unsecured object in the room—from the desk chair to the coffee pot—is sent flying. Shaken loose by the shuddering and jolting of the building, dust and ceiling particles drift down like snow. Then the lights flicker and go out. Remembering to “drop, cover, and hold,” you crawl under the nearest table, hold on tight, and tell yourself that the shaking should last only a few seconds more . but it goes on and on. This is it: the Big One. The Cascadia subduction zone has just unleashed a magnitude 9.0 earthquake. Are you prepared? IF YOU LIVE IN NORTHERN CALIFORNIA, WASHINGTON, OREGON, OR BRITISH COLUMBIA, YOU LIVE IN CASCADIA, a region remarkable for its stunning mountain ranges, rich farmlands and vineyards, beautiful beaches, great rivers, and green forests. It is a region of vibrant communities, busy international ports, and thriving businesses. Residents and visitors alike enjoy the cultural offerings of Cascadia’s cities and the diversity of outdoor activities at its natural areas. But the geologic forces that shaped the Northwest are still active: Cascadia is a region of earthquakes. The Cascadia subduction zone is one of the principal sources of concern. Lying mostly offshore, this plate interface is a
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