LANDSLIDE AND LIQUEFACTION MAPS FOR THE LONG BEACH PENINSULA, PACIFIC COUNTY, WASHINGTON: Effects on Tsunami Inundation Zones of a Cascadia Subduction Zone Earthquake by Stephen L. Slaughter, Timothy J. Walsh, Anton Ypma, Kelsay M. D. Stanton, Recep Cakir, and Trevor A. Contreras WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Report of Investigations 37 October 2013 DISCLAIMER Neither the State of Washington, nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the State of Washington or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the State of Washington or any agency thereof. WASHINGTON STATE DEPARTMENT OF NATURAL RESOURCES Peter Goldmark—Commissioner of Public Lands DIVISION OF GEOLOGY AND EARTH RESOURCES David K. Norman—State Geologist John P. Bromley—Assistant State Geologist Washington Department of Natural Resources Division of Geology and Earth Resources Mailing Address: Street Address: MS 47007 Natural Resources Bldg, Rm 148 Olympia, WA 98504-7007 1111 Washington St SE Olympia, WA 98501 Phone: 360-902-1450; Fax: 360-902-1785 E-mail: [email protected] Website: http://www.dnr.wa.gov/geology Publications List: http://www.dnr.wa.gov/researchscience/topics/geologypublications library/pages/pubs.aspx Online searchable catalog of the Washington Geology Library: http://www.dnr.wa.gov/researchscience/topics/geologypublications library/pages/washbib.aspx Washington State Geologic Information Portal: http://www.dnr.wa.gov/geologyportal Suggested Citation: Slaughter, S. L.; Walsh, T. J.; Ypma, Anton; Stanton, K. M. D.; Cakir, Recep; Contreras, T. A., 2013, Landslide and liquefaction maps for the Long Beach Peninsula, Pacific County, Washington—Effects on tsunami inundation zones of a Cascadia subduction zone earthquake: Washington Division of Geology and Earth Resources Report of Investigations 37, 3 sheets plus 27 p. text. Published in the United States of America © 2013 Washington Division of Geology and Earth Resources Contents Introduction ........................................................................................................................1 Seismically Induced Ground Failures .................................................................................2 Soil Liquefaction ......................................................................................................... 2 Landslides .................................................................................................................... 4 Regional Geology and Physiography ..................................................................................4 Method of Analysis .............................................................................................................5 Results and Discussion .......................................................................................................5 Recommendations ...............................................................................................................7 Acknowledgments ..............................................................................................................8 References Cited .................................................................................................................9 Appendix A. Technical Description of Landslide Vulnerability Modeling from a Cascadia Subduction Zone M9+ Earthquake ................................................. 13 Introduction ............................................................................................................... 13 Background ................................................................................................................ 13 Methods ..................................................................................................................... 14 Topography ......................................................................................................... 14 Geology and Soils .............................................................................................. 14 Groundwater ....................................................................................................... 15 Shallow Landslides ............................................................................................. 16 Discussion and Results .............................................................................................. 17 Shallow Rapid Landslides .................................................................................. 17 Newmark’s Analysis .................................................................................... 18 Deep-Seated Landslides ..................................................................................... 18 Other Landslide Hazards .................................................................................... 18 Appendix B. Technical Description of Liquefaction Susceptibility and Initiation Modeling from a Cascadia Subduction Zone M9+ Earthquake ................. 19 Introduction ............................................................................................................... 19 Background ................................................................................................................ 19 Methods ..................................................................................................................... 20 Geotechnical Borehole Logs .............................................................................. 20 Groundwater and Wetlands ................................................................................. 21 Liquefaction Susceptibility and Initiation Analysis ............................................ 21 Seismic Survey ................................................................................................... 22 Liquefaction Hazard Mapping ............................................................................ 22 Discussion and Results .............................................................................................. 22 Liquefaction Susceptibility and Initiation .......................................................... 23 Seismic Survey to Determine Shear-wave Velocity ........................................... 24 Appendix C. Analyzed Borehole Data Table .................................................................... 26 iii FIGURES Figure 1. Location of the Long Beach Peninsula study area.. .............................................2 Figure 2. Photos of seismically induced liquefaction damage to transportation networks ...............................................................................................3 Figure 3. Map showing documented liquefaction sites from the 2010 Chile M8.8 earthquake ................................................................................................4 Figure 4. Block diagram of the Cascadia subduction zone .................................................5 Figure 5. Tsunami inundation zones from a tsunami initiated by a M9+ Cascadia subduction zone earthquake on the Long Beach Peninsula. .........................6 Figure A1. Graphs of groundwater levels from select wells. ............................................ 15 Figure A2. Map of groundwater monitoring sites on the Long Beach Peninsula. ............ 16 Figure B1. Map of an evacuation route crossing several peat deposits and wetlands on the Long Beach Peninsula ............................................................... 23 Figure B2. Graph of active and passive shallow seismic survey Vs100 data at five locations in the study area .............................................................................. 25 TABLES Table B1. USCS soil properties for boreholes analyzed for the report area ...................... 20 Table B2. Characterization of overall site susceptibility to liquefaction hazards ............. 21 Table B3. Criteria used in this report to provide a soil liquefaction hazard rating ............ 22 Table B4. National Earthquake Hazards Reduction Program recommended site classifications ..................................................................................................... 25 Table C1. Initiation of liquefaction in terms of the factor of safety for a layer ................. 26 SHEETS Sheet 1. Shallow landslide vulnerability during a dry period for a Cascadia subduction zone magnitude 9+ earthquake for the Long Beach Peninsula, Pacific County, Washington Sheet 2. Shallow landslide vulnerability during a wet period for a Cascadia subduction zone magnitude 9+ earthquake for the Long Beach Peninsula, Pacific County, Washington Sheet 3. Liquefaction initiation hazard for a Cascadia subduction zone magnitude 9+ earthquake for the Long Beach Peninsula, Pacific County, Washington iv Landslide and Liquefaction Maps for the Long Beach Peninsula, Pacific County, Washington: Effects on Tsunami Inundation Zones of a Cascadia Subduction Zone Earthquake Stephen L. Slaughter, Timothy J. Walsh, Anton Ypma, Kelsay M. D. Stanton, Recep Cakir, and Trevor