South Puget Sound Earthquake (pre)History by Timothy J. Walsh Washington Department of Natural Resources Division of Geology and Earth Resources P. O. Box 47007, Olympia, WA 98504-7007 Photo by Bill Shilts Geologic Hazards • Landslides • Earthquakes • Tsunamis Landslides that have caused significant damage in Washington are generally deep-seated and slow moving or shallow and rapid. Deep-seated landslides tend to have a delayed response to climatic events, generally being triggered by the accumulation of rainfall over weeks or even years. Shallow, rapid landslides respond quickly to large storms and commonly accompany major floods. Either can be triggered by earthquakes. Significant historic deep-seated lanslides include Aldercrest-Banyan in Kelso that destroyed 135 homes in 1998, costing $50 million in federal disaster aid; Carlyon Beach in northwest Thurston County in 1998, destroying 36 homes; Rolling Bay on Bainbridge Island in 1997, destroying a home and killing its 4 occupants; Piper-Rock Creek in Stevenson in 2007 and continuing to the present, destroying 2 homes and endangering a sewage treatment plant; and the SR 530 slide that killed 43 people. Head scarp, Aldercrest-Banyan landslide, 1998 136 homes were lost in this landslide Coastal Zone Atlas, Carlyon Beach Slope stability map of the Carlyon Beach area, northwest Thurston County (near Olympia), 1980 Carlyon development Mapped as intermediate to unstable terrain Carlyon Beach Landslide In February 1999, after 3 consecutive years of above- average rainfall, movement began on a dormant landslide near Olympia, eventually forcing thirty-six families from their homes. This landslide into Tacoma Narrows occurred 3 days after the 1949 earthquake and generated an 8 ft tsunami at Gig Harbor that reflected back and drowned all of these houses 3 ft deep This landslide at Salmon Beach,triggered by the Nisqually earthquake (2001) damaged the houses that survived in 1949 Shallow rapid landslides occur during and soon after significant rain or rain-on-snow events. The National Flood Insurance Program includes mudflows in its definition of flood, so statistics on damage from shallow rapid landslides are not readily separable from flood damage statistics. The 1997 disaster cost about $300 million, and it appears that well more than half of that was from debris flows. Flood disasters in 1981-82, 1984, 1996, 2006, 2007, and 2009, have significant contributions from debris flows. Including deep-seated landslides, a reasonable average annual loss from landslides over the last 35 years is >>$20 million. Perkins Lane Landslide 1997 This reactivated slide area on Perkins Lane in the Magnolia District of Seattle eventually claimed five houses. This dive shop in west Seattle was destroyed by a landslide that came through its back wall and out the front (January, 1997) This landslide 2 weeks later knocked five rail cars into Puget Sound Rolling Bay, Bainbridge Island, 1997 WA DOE Website Tragedy struck on January 19th, 1997. Within three seconds, 2,000 tons of rock, trees, and soil crushed the Herren home, killing all four family members. On December 3, 2007, following an intense rain, a small slump that picked up water in the stream, bulked up, and transformed into this destructive debris flow... Foundation of brown building and destroyed this restaurant just outside of Olympia, which was rebuilt on the same foundation These houses were damaged by debris flows in January, 2009 And North Fork Stillaguamish on March 22, 2014 What tools are available for planners to mitigate landside hazards? Unfortunately, the availability and quality are uneven. Puget Sound coastal bluff landslide hazard maps for Thurston Co. Landslide hazard mitigation begins with hazard identification. The Division of Geology inventories landslides at https://fortress.wa.gov/dnr/geology/?Theme=natural_hazards Zooming in allows delineation of individual landsides With the identify tool, any individual landslide can be queried for source and for more information The interactive map application (https://fortress.wa.gov/dnr/g eology/) allows you to choose which layers to overlay (for example, compare hazard zones with the underlying geology). Point data can be viewed in relation to surface geology and base map information. The application currently has different map themes, each of which can be accessed through the mapping application itself, or the Washington State Geologic Information Portal main page (http://www.dnr.wa.gov/geol ogyportal). However, this inventory was not systematically collected, is not well documented, is geographically spotty, and is of uneven quality. LIght Detection And Ranging • Airborne scanning laser rangefinder • Differential GPS • Inertial Navigation System 30,000 points per second at ~15 cm accuracy • $400–$1000/mi2, 106 points/mi2, or 0.04–0.1 cents/point Extensive filtering to remove tree canopy (virtual deforestation) Largely as a consequence of the Oso landslide, the Division of Geology received an increase in funding for the 2015-2017 Biennium Received $4.6 million and 7 employees Five in landslide hazards group Two to run a state-wide lidar survey; $1.2 million/year to collect lidar 10-meter DEM from contours 12-ft DEM from LIDAR Landslide mapping • Inventory > Susceptibility > Hazard > Risk Mapping Type Definition 1. Inventory Location and characteristics of existing landslides Location and characteristics of potential landslide; 2. Susceptibility areas with a potential to experience future landslides 3. Hazard Estimated annual probability of a landslide Estimated probability of the occurrence and the 4. Risk probability of the consequence Safeguarding Against Landslide Hazards • Research into property • Get advice from licensed geologist or engineering geologist • Leave a safe setback from steep slopes / bluffs • Keep plants on slopes below house • Reduce surface erosion – avoid discharge onto slope • Reduce ponding and infiltration • Maintain and improve vegetation • Maintain drainage • Don’t irrigate or put drainfields at top of slope / bluff • Don’t dump on slope • Don’t change natural drainage • Don’t cut into the toe of slope • Don’t overlook slide hazards (may slide once every several decades or so) Avoidance is your safest bet! Geologic Hazards • Landslides • Earthquakes • Tsunamis Washington has a high exposure to earthquake and has experienced 15 damaging events since 1872. Geologic evidence demonstrates substantial hazard from faults that have not ruptured since European settlement of the Pacific Northwest. These include the Seattle, Tacoma, Olympia?, southern Whidbey Island, Devil’s Mountain, Canyon River, Boulder Creek, Toppenish Ridge, and Saddle Mountain faults, which are all capable of earthquakes larger than M6.5 at shallow, and therefore highly damaging, depths. Additionally, there is substantial evidence that the Cascadia subduction zone is active and has generated earthquakes >M9.0 (Atwater and others, 2005) The earliest record of earthquakes in south Puget Sound is from 1833 FORT NISQUALLY, PUGET SOUND Saturday, June 29, [1833] "Mr. Heron returned about 9 this morning to breakfast. Afterwards we mounted the north bank of Coe by the path & were occupied nearly all day in collecting specimens of the soil at every hundred yards length from the summit of bank to the ploughed land. H. & I on horseback. While thus engaged our three attendants, McKie, Brown & Peter Tahi, the islander, felt the earth under them shake violently at least twice. Brown first exclaimed, & seemed much alarmed - He & McKie were on their knees at the time & felt violently lifted up, the sensations of Peter I could not ascertain, Mr. H[eron] & I [on horseback] did not perceive anything remarkable - this happened at 20 minutes from 2 by Rendall's watch, which is not far wrong. On returning to the house we learn't that the shock had been felt there, the boards in the floor of house rattling together. The Indians were much struck & said "The Chief's (Heron's) medicine is strong, he has gone up the hill to shake the grounds." In some quarter of the globe, perhaps the Almighty has wrought some dire devastations by earthquake, one of the most powerful & calamitous instruments of chastisement employed against Mankind. The steep & broken faces to Eastward of the islands in the sound render it probable, that they have been severed from the main shore by an earthquake." Washington has earthquake hazards from three different source zones Pioneer Square,1949 Pioneer Square,2001 Deschutes Parkway, 1965 Deschutes Parkway, 2001 Salmon Beach, 2001 Salmon Beach, 1949 BCF DDMF SPF,UPF LRF SWIF SMF FCF SF RMF CRF TF OF SMF TRF SHZ SPF OWL LRF, Little River fault; SMF, Saddle Mountain East and West faults; FCF, Frigid Creek fault; CRF, Canyon River fault; OF, Olympia fault; SHZ, St. Helens Zone; TF, Tacoma fault; SF, Seattle fault; SWIF, Southern Whidbey Island fault; SPF, Strawberry Point fault; UPF, Utsalady Point fault; DDMF, Darrington-Devil’s Mtn. Fault; RMF, Rattlesnake Ridge fault; TRF, Toppenish Ridge fault; SPF, Satus Pass fault; SMF, Saddle Mountain fault; OWL, Olympic-Wallowa Lineament. From Sherrod and others, 2008 SMF CRF from Clement and others, BSSA, 2010 In order to assess faults, we need to use new technologies to locate faults and dig trenches to expose them for study from Clement and others, BSSA, 2010 Another suspected fault runs through the Olympia area. We call it the Olympia structure but some people call it the Olympia fault. It was initially identified on the basis of geophysical information. There is also paleoseismic data in support of an Olympia fault. Jack Odum and Bill Stephenson have recently done seismic reflection profiling along Steamboat Island Road and have preliminarily made some interpretationsof the Olympia structure (or maybe it is a fault). Skokomish Delta terrain and magnetic contacts. This map shows SRTM topography. D The scarp shows up clearly, even in these Shuttle data. Notice the topographic lineament northwest of and on strike with the scarp (yellow arrow). This lineament is intriguing but has a sense of offset (southwest side up) opposite from the sense of the scarp.