WASHING1rON STATE EARTHQUAKE:HAZARDS by LINDA LAWRANCE NOS , ANTHONY QAMAR, AND GERALD W. THORSEN WASHING TON DIVISION OF GEOLOGY AND EARTH RESOURCE INFORMATION CIRCULAR 85 1988 WASHINGTON STATE DEPARTMENT OF Natural Resources Brian Boyle - Commissioner of Public Lands Art Stearns - Supervisor Division of Geology and Earth Resources Raymond Lasmanis, State Geologist Cover photo: Damage to an unreinforced masonry building in downtown Centralia in 1949. A man was killed by the falling upper walls of this two-story corner building. Unreinforced masonry walls, gables, cornices, and partitions were the most seriously damaged structures in the 1949 and 1965 earthquakes. Inferior mortar and inadequate ties between walls and floors compounded the damage. (Photo from the A. E. Miller Col­ lection, University of Washington Archives) -- WASHING TON ST ATE EARTHQUAKE HAZARDS by LINDA LAWRANCE NOSON, ANTHONY QAMAR, AND GERALD W. THORSEN WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES INFORMATION CIRCULAR 85 1988 • . ' NaturalWASHING10N STATE Resources DEPARTMENT OF Brtan Boyle • Commasloner 01 P\lbllc Lands Art Steorns • Supervisor Divisfon 0 1 Geology and Earth Resources Raymond Lasmanis. State Geo!ogisl The authors gratefully acknowledge review of the manuscript of this publication by members of the Geophysics Program. University of Washington. This report is available from: Publications Washington Department of N arural Resources Division of Geology and Earth Resources Mail Stop PY-12 Olympia, WA 98504 The printing of this report was supported by U.S. Geological Survey Earthquake Hazards Reduction Program Agreement No. 14-08-0001-A0509. This publication is free, but please add $1.00 to each order for postage and handling. Make checks or money orders payable to the Department of Natural Resources. Because we have a limited number of copies, please write or telephone ((206) 459-6372] the Division if you wish to place a large order. The contents of this book are not copyrighted. However, copies may not be reproduced for sale. This book is printed on acid-free paper. Printed in the United States of America. CONTENTS Summary ....... ....... ..... .. .. .. .. .. ... ................................. .. .. ..... .. .. .. l Introduction ... ......... .. .... .. .. .. .. .. ........... .. ............................. ..... .. ... 3 What are earthquakes? ..... ... .. ..... .. .. ........... .. .. .. .. ........................ ... .. ..... 5 How are earthquakes measured? . ....................................................... .... .... 11 What causes earthquakes? .. ... ............................................... ..... ............. 15 Plate tectonics theory .. ... ..................................................... ........ .... 15 Plate tectonics and earthquakes in the northwestern United States ................................. .... 15 Where do earthquakes in Washington occur? ..... .. ....................... ......... .................21 Washington's largest reported earthquakes ............................. .. ........... ............2 1 Earthquakes recorded by the University of Washington seismograph network ............... .. .. .. .. .. .2 1 When and where will the next big earthquake occur? .... ... .. .. ...................... .. ....... .. ... .27 What causes damage? .......... .. .. .. ... .. ... ...... .................... ... .. .. ............ 29 Direct causes . .. .. ... ..................................................... .... .............29 Secondary causes of earthquake damage .... .. ......... .. .................... .. ........ ... 30 Where has earthquake damage occurred in Washington State? ............... ..... .. .. ................. .49 1872 North Cascades earthquake ................................. ..... .. .. .. ............... ... .49 1936 Milton-Freewater earthquake ......................................... .. ... .............. 49 1939 Puget Sound earthquake . .. .. .... .. ............................. .. ............. ..49 1945 Puget/Cascades border region earthquake ........................ .. .. .. .. ...... ...........49 1946 Puget Sound earthquake . ..... ........... ........................ .. .. .. .. ............49 1949 Olympia and 1965 Seattle-Tacoma Puget Sound earthquakes . .. .. ... ......... ........... .. .. 50 How can we reduce earthquake losses in Washington? . .. .. .. .. ... .......... ................ ... ... 53 Understanding earthquake risk . .. .. ... ... .. ........ .......................... .. ...........53 Risk reduction .. ..... ..................................... .... .. ..................... .. .. 59 Risk reduction policy ........................................ ... ........................ ..6 1 Glossary .............. ........ ...................... .........................................63 References cited ....................................... .. ..................... ... .. ...... 67 Selected catalogs containing information about earthquakes in Washington and adjacent areas ...............73 Publications of the Federal Emergency Management Agency ................... ..... ....... ........ 77 ILLUSTRATIONS Figure 1. Block diagrams of fault types .... ....................... .. .. .. ........... .... ........ 5 Figure 2. Diagrams of near-surface ground motions produced by seismic waves . .. ...... .. ... ...... ... ... 6 Figure 3. Map showing location of active seismograph stations in the Pacific Northwest in 1987 . .. ..... .. ...... 7 Figure 4. Sketch of components and dimensions of a typical remost seismograph station . .. ............... ..... 8 Figure 5. Seismograms illustrating the range of ground motions commonly recorded in Washington and Oregon ... : .9 Figure 6. Method for calculating epicentral distance and magnitude of an earthquake ......... ............... 12 Figure 7. Isoseismal map for the Seattle-Tacoma earthquake of 1965 ............. ............... .. .. ..... 14 Figure 8. Map showing relation between major tectonic plates and earthquakes ........... ... .......... 16 Figure 9. Cutaway view of the Earth ............. ......................... .. ... ................... 17 Figure 10. Diagram illustrating three types of plate boundaries ............................... ............ 17 Figure 11. Cross sections of Washington showing plate convergence and earthquake hypocenter locations ...... 18 Figure 12. Map showing epicenters of selected earthquakes in the Pacific Northwest since 1960 . .. .. .......... 19 Figure 13. Map showing epicenters and dates of the largest Pacific Northwest earthquakes between 1872 and 1987 .23 Figure 14. Map showing epicenters of Washington earthquakes recorded from 1982 to 1987 (Mc~ 2.0) ......... 24 iii ILLUSTRATIONS, continued Figure 15. Map showing faults in Washington known to be active or thought to have been active in the last 10,000 years .......................... .. .. ..................... .. .........25 Figure 16. Aerial view of the Saddle Mountain faults near Lake Cushman, Olympic Peninsula ....... .... ... 30 Figure 17. Photograph showing evidence for subsidence in coastal Washington, buried marsh ............... ... 31 Figure 18. Photograph showing evidence for subsidence in coastal Washington, ghost forest ... ............... 31 Figure 19. Photograph of a landslide in fill near Olympia, 1965 .............. ................. ..........32 Figure 20. Photograph of landslide, Tacoma Narrows, 1949 .............................................. 34 Figure 21. Photograph of road damage caused by liquefaction, Olympia, 1965 ........................... .. 34 Figure 22. Photograph of sand blows, Olympia, 1965 . .................. .. ............................... 35 Figure 23. Tide gage records showing tsunami waves from the 1964 Alaska earthquake . ................ ....... 37 Figure 24. Map showing tsunami damage in coastal Washington from the 1964 Alaska earthquake ............38, 39 Figure 25. Photograph of stripped dunes, coastal Washington ............................................. 39 Figure 26. Diagram showing structural components of a building ....... ............ ............. ....... 40 Figure 27. Photograph showing failure of unreinforced masonry during the 1965 earthquake . .. ........... .... .40 Figure 28. Photograph of damage at the Fisher Flouring Mills, 1965 ..... .. ............................... .41 Figure 29. Photograph of collapsed roof, Puyallup High School, 1949 ... .. ............ .. .................. .42 Figure 30. Photograph of a collapsed parapet wall, Olympia, 1949 . .. ........... .........................43 Figure 31. Photograph of a damaged chimney, Kelso, 1949 ......... .................. .. .. ...............44 Figure 32. Photograph of fallen light fixtures in an Olympia school, 1965 . .............. .. ...............44 Fig\Jfe 33. Photograph of fallen library shelves, 1949 ....................................................44 Figure 34. Photograph of Boeing Company tapes scattered by the 1965 earthquake ........... .. ... ......... .45 Figure 35. Photograph of windows broken in a Tacoma store by the 1965 earthquake ........................ .45 Figure 36. Photograph of government files disturbed by the 1965 earthquake ................ .............. .45 Figure 37. Photograph of damaged radio tower, 1949 ................... .. ...............................46 Figure 38. Photograph of damage at Lower Van Norman Dam, California, 1971 ..............................47 Figure 39. Photograph of shifted ground in Seattle, 1965 ............... .. ................ ...............