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

Slope stability map of the Carlyon Beach area, northwest Thurston County (near Olympia),1980

Carlyon development

Mapped as intermediate to unstable terrain

Coastal Zone Atlas, Carlyon Beach

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.

Carlyon Beach Landslide

This landslide at Salmon Beach,triggered by the Nisqually earthquake (2001) damaged the houses that survived in 1949

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

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

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.

WA DOE Website

Rolling Bay, Bainbridge Island, 1997

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...

and destroyed this restaurant just outside of Olympia, which was rebuilt on the same foundation

Foundation of brown building

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/geology/) 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/geologyportal).

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 BienniumReceived $4.6 million and 7 employees

Five in landslide hazards groupTwo 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 Definition1. Inventory Location and characteristics of existing landslides

2. Susceptibility Location and characteristics of potential landslide; areas with a potential to experience future landslides

3. Hazard Estimated annual probability of a landslide

4. Risk Estimated probability of the occurrence and the 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

Salmon Beach, 1949

Salmon Beach, 2001

Deschutes Parkway, 2001Deschutes Parkway, 1965

CRF

FCFSMF

OF

TF

SF

SWIF

DDMF

SPF,UPFLRF

RMF

SMF

TRF

SPF

OWL

SHZ

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.

BCF

From Sherrod and others, 2008

CRF

SMF

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. 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. Also notice that the magnetic contact along the southwest margin of the magnetic low (anomaly B) continues northwest of the scarp and along the topographic lineament.

The purple dotted line shows the location of the profile in the next slide.

A

B

D

C

Some background. Washington is located in the northeast corner of the Ring of Fire

Distribution of magnitude 5

or greater earthquakes, 1980 - 1990

Distribution of some of

the world’s major

volcanoes

These trenches are the loci of large earthquakes that get progressively deeper as the subducting slab gets progressively deeper

Relationship of earthquake depth to subduction zones. This is the geological context of the earthquake and tsunami hazard in the Pacific Ocean.

And that was reasonable at the time. Note that there is no trench off the Pacific Northwest, even though there is a ridge system. Was there really an active subduction zone here?

Note that the coast of Washington has very few earthquakes, and none on the subduction zone. How did we get to our present understanding?

In 1969, the Pacific Northwest Seismic Network was installed, beginning with 6 stations. After a year of monitoring, no earthquakes had been detected on the plate interface and a Wadati-Benioff Zone was not obvious. Crossontentatively concluded that subduction had ceased.

In 1984, John Adams of the Geological Survey of Canada, suggested that if there were great earthquakes in Cascadia, they should trigger landslides from the edge of the continental shelf, and that oceanographic studies by Vern Kulm and Gary Griggs had identified deposits of these landslides.More on that later.

In 1979, Ando and Balasz, on the basis of limited vertical geodetic modeling, concluded that Washington was tilted down to the east and that subduction was still occurring but was aseismic.

In 1981, Savage and others, on the basis of horizontal geodetic modeling, concluded that the subduction zone should be seismically active and that the vertical geodetics of Ando and Balasz were difficult to reconcile.

Meanwhile, the Washington Public Power Supply System (WPPSS) attempted, with only a 20% success rate, to build 5 nuclear power plants in Washington. The last previous nuclear power plant in the northwest, Trojan in northwest Oregon, was licensed and began operating in 1975. The NRC, which was created in 1975 to replace the AEC, required a much more rigorous seismic safety review of these new plants and substantially funded research into Cascadia earthquake hazards.

The NRC funded Tom Heaton, then with the USGS at CalTech, to study the seismic potential of Cascadia, ostensibly with the hope that he would collaborate with CalTech professor Hiroo Kanamori, one of the world’s premier experts on subductionzone seismology. In 1984, their study concluded that Cascadia had much in common with seismically active subduction zones elsewhere and that Cascadia was probably seismically active as well.

At about this time, an estuarine paleoecologist with the USGS in Menlo Park transferred to the USGS office at the University of Washington and began to search for evidence of the coastal tilting modeled by Ando and Balasz. Instead of uplift, however, he found evidence of abrupt subsidence at the Waatch River near Neah Bay, followed by slow uplift. Eventually, Brian and many colleagues found this pattern repeated all along the Cascadia coast from northern California to the northern end of Vancouver Island.

The largest instrumentally recorded earthquake in history was a Magnitude 9.5 in southern Chile in 1960.

Queule, Chile, in Valdivia Province, before earthquake

Queule, Chile, in Valdivia Province, after earthquake and tsunami

And then in 1964a Magnitude 9.2 earthquake struck Alaska

Drowned forest in Girdwood, Alaska, killed in 1964

Drowned forest along the Copalis River, Washington, killed in A.D. 1700

Earthquake-induced ground crack

Placer River Silt

A.D. 1700 Ground surface

1,100 year old ground surface

from Brian Atwater

Here is what was happening. Between earthquakes, uplift along the coast causes the tilting that Ando and Balasz observed, but the earthquake causes the abrupt subsidence that Atwater and others have observed.

Tsunami sands

A.D. 1700 ground surface

Right, subsided marsh along the Niawiakum River, southwest Washington. Below, note pitfalls of working in tidal marshes.

But does the entire subduction zone rupture at once or is it filled by smaller events?

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Model by Kenji Satake

Regardless of the type of earthquake, reconnaissance liquefaction susceptibility and ground shaking amplification maps such as these made by Division of Geology for every county can help assess your local hazard and vulnerability. These need to be used in conjunction with the National Seismic Hazard map.

Geologic Hazards

• Landslides

• Earthquakes

• Tsunamis

Here is the historic context. On April 1, 1946, a magnitude 8.0 (Mw) earthquake with the source in the Aleutian Islands to the south of Unimak Island generated a tsunami that destroyed this five-story lighthouse, located 9.8 m above sea level.

Only the foundation and part of the concrete sea wall remained. All five occupants were killed. The waves deposited debris as high as 35 m above the sea. Although little damage occurred in Alaska, except at Scotch Cap, the tsunami was one of the most destructive ever to occur in the Hawaiian Islands. Photo credit: U.S. Coast Guard.

The school children noted that the water had receded. Many went down to the shore to watch

•At least 24 people were killed here, many of whom were children playing by the waterfront. The tragedy of the 1946 tsunami prompted the U.S. Coast and Geodetic Survey to establish the Tsunami Warning System

This woman was a small child at the time , living just above the inundation limit. She still places flowers here every day.

In 1964, a large earthquake in Alaska generated a tsunami that was damaging in Alaska and the west coast of the U. S. . from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527

Prince William Sound, Alaska 1964 March 28 03:36:14 UTC (March 27 local) Magnitude 9.2

This earthquake generated a Pacific Ocean-wide tsunami that killed 110 people, 8 here in Crescent City, CA. Note fire in background. This event led to the opening of a second tsunami warning center in Palmer, Alaska.

Highway 109 bridge over Copalis River

Highway 109 bridge over Joe Creek

Tsunami damage from the 1964 Alaska earthquake

House torn apart at Pacific Beach

The wave here was about 10-12 feet.

Tide gage records showing tsunami waves from the March 27, 1964, Alaska earthquake (M 9.2) as recorded at four sites in Pacific Northwest. Superimposed on the normal tides with a period of about 12 hours (see predicted curve at Friday Harbor) are more rapid oscillations with periods of about 1/2 hour caused by tsunami waves. Note the differences in tsunami wave amplitudes at different sites.

This tsunami led to the establishment of a second tsunami warning center in Palmer, Alaska.

It also led to studies of maximum expected tsunami heights along the west coast for earthquakes having return periods of 100 and 500 years for inclusion in the flood insurance program.

Only distantly generated tsunamis were considered

But now we know that near-field, or locally generated tsunamis generated by a Cascadia subduction zone earthquake can happen and will arrive on the Washington coast in less than 45 minutes. For these events, as was the case in Banda Aceh, the earthquake must be the warning. Citizens must know where to evacuate from and where to evacuate to, and must do so quickly and on foot. This problem was the driving motivation for the NTHMP inundation mapping program.

In the early 1990’s, a confluence of 3 events---the realization that the Cascadia subduction zone produced both major earthquakes and major tsunamis; the 1991 Petrolia earthquake, which generated a small local tsunami; and the 1994 Kuril Islands tsunami warning; ---led the Senate Appropriations Committee, chaired by Mark Hatfield, to direct NOAA to form a partnership with the 5 Pacific states to develop a plan to safeguard the west coast from local tsunamis

Civilization exists by geological consent—subject to change without notice

Will Durant