Nisqually Earthquake, Washington Mw 6.8

WARNING: Provisional report, subject to revision

The Geologic Hazards Team from Golden, CO has sent 4 teams of earthquake investigators to the Seattle, WA area. These teams are gathering information on:

Aftershocks
Earthquake damage and felt reports
Building, highway, and bridge structural problems
Landslides, liquefaction, sand boils/blows, ground cracks/ruptures

Map

Map

Earthquake location map from National Earthquake Information Center (NEIC)

Earthquake location map from National Earthquake Information Center

Photo Gallery

Landslides, rockfalls, ground cracks related to the Nisqually earthquake.

General Meetings

Held at the University of Washington, Moore Hall, Seattle, WA

1st General Meeting held March 1, 2001

2nd General Meeting held March 2, 2001

3rd General Meeting held March 3, 2001

No more general meetings to be held after the 3rd.

Report #1

From Randy Jibson, U.S. Geological Survey, Geologic Hazards Team, Golden, CO. via phone conversation and in person.

U.S. Geological Survey, Geologic Hazards Team (Golden, CO), specialist in landslides related to earthquake triggers. After two days in the field there is very little evidence of landsliding. We have done follow up on media reported landslides, visiting most of the reported significant landslides and none are dramatic. There has been little shaking to trigger landslides, with less than 0.2 gravity acceleration . We have been determining the extent or furtherest limit of the triggered landslides by sending teams in different compass directions. Dave Keffer (USGS-Menlo Park, CA) covered South and Southeast, Rex Baum (USGS-Golden) and Alan Chleborad (USGS-Golden) covered Northeast, Ed Harp (USGS-Golden) the islands and the sound area.

Report #2

From Rex Baum, Al Chleborad, Ed Harp, Randall Jibson, David Keefer, and Scott Miles, U.S. Geological Survey Geologic Hazards Team, Golden, CO. and U. S. Geological Survey, Menlo Park, CA, written. Report is incomplete and preliminary as of this time. About half of the team are heading home either Sunday or Monday, March 3rd or 4th having completed their work.

Report #2 Follow-up (added March 6th, 2001, 9:35am)

Landslides triggered by the February 28, 2001, Seattle, Washington, earthquake are sparsely concentrated yet spread over a wide area. Due to the depth of the earthquake and the relatively low accelerations of the ground shaking, there appear to be no dense concentrations of landslides in any one area, however, the scattered failures that have occurred have resulted in considerable impact to people and property.

Three teams of landslide experts from Golden, Colorado, and Menlo Park, California, and Seattle, Washington, have been traveling throughout the earthquake-affected area to document the distribution and extent of the landslides and assess any remaining and future hazard posed by them. As hazards are noted , appropriate authorities are notified. Some of the most notable landslides are:

Salmon Beach Landslide

The landslide with the highest hazard to date is a rock/soil slide from the bluffs above the community of Salmon Beach north of the Tacoma Narrows bridge near Tacoma, Washington. A rock/soil slide of about 1000 cubic meters has demolished two houses located at the base of the steep bluff along the shores of Puget Sound. A larger slide of about 10,000-20,000 cubic meters of material remains poised on the slopes above the houses and threatens 5 to 6 additional dwellings. This larger slide has already slid 20 to 25 feet and has a scarp near the top of the bluff extending for about 60 meters below the top of the bluff. We have alerted Pierce County officials, they have dispatched a geotechnical engineer to evaluate the situation. She called back yesterday and reported that eight houses have been red tagged as a result of the inspection.

Maple Valley Landslides

Two notable landslides occurred near the suburb of Renton along the Cedar River drainage. The larger of the two blocked the Cedar River and created a landslide dammed reservoir for a time until earth-moving equipment could be sent to the site and a ditch dug through the slide debris. This landslide consisted of a rock fall in weakly cemented sandstone falling upon colluvium at the base of the slope which may have liquefied producing a highly fluid debris flow that dammed the river.

A second landslide just upstream from that damming the river formed within saturated colluvium at the base of a steep bluff. The failure appears to have been caused by the liquefaction of the colluvium. The debris flow slammed into a house about 70 m downslope nearly breaking it in two and filling about half of the structure with debris. A woman who had just run outside the house during the earthquake shaking narrowly avoided being buried by the landslide debris that filled the kitchen where she had been standing.

Landslide on U. S. 101 in Olympia

A debris flow of about 15,000 cubic meters occurred in the artificial roadway fill of the highway removing one lane of a four-lane highway and flowing downslope between two houses before ponding on the surface of a street about 250 m downslope. The failure may have resulted from liquefaction of the highway fill or from a broken water pipe that was observed in the landslide scarp. Steve Palmer, a geologist with Washington Department of Natural Resources, reported that the pipe was flowing water from the break when he observed the landslide on the day of the earthquake.

Capitol Lake Lateral-Spreading Landslides

Several lateral-spread landslides occurred around the margins of Capitol Lake in Olympia. The dike on the south margin of the lake failed in several places; some of the cracks that formed contained ejected silt, which indicates that liquefaction occurred. Water and sewer lines crossing the area were broken in places. Deschutes Parkway on the west margin of the lake is closed in several places owing to slumping along the edge of the lake.

Report #3

From Jim Dewey and Margaret Hopper, U.S. Geological Survey, Geologic Hazards Team, Golden, CO. Report via phone conversation.

We have been working in the Southern Puget Sound area in and east of Olympia. We see some similarity between damage caused by this shock and damage caused by the earthquake of April 13th, 1949. Olympia was strongly affected by both shocks, with many damaged chimneys in some parts of town, damage to the capitol buildings, and damage to upper walls and parapet walls of unreinforced masonry buildings.

These similarities in damaged are expected, because the 1949 and 2001 earthquakes occurred at nearly the same location and had nearly the same magnitudes. What we find surprising are the differences in effects of the 1949 and 2001 shocks in towns east of Olympia. We have visited a half dozen towns that experienced high damage in 1949 but only light damage in the recent shock. We are convinced that the shaking was less in these towns in this recent earthquake than it was in 1949, at least at the frequencies that caused damage to unreinforced masonry buildings. Although the faulting processes that produced the two earthquakes are generally similar, it is possible that differences in the details of the faulting process are responsible for the observed differences in shaking.

Report #4

From E.V. Leyendecker, U. S. Geological Survey, Geologic Hazards Team, Golden CO., structural engineer specialized in earthquake and structure response. Having completed my field survey I am leaving Sunday, March 4th.

I visited Olympia first and the noted that the State Capitol has cracks in the supporting columns that hold up the dome. I next visited Seattle, south of Pioneer Square and noted little major structural damage. I spent part of the day with a structural engineer from Seattle and coordinated access to a damaged building database when it becomes available. I also made contacts with the Department of Transportation in Olympia and will get additional data regarding bridge damage. The U.S. Geological Survey had another engineer here from Menlo Park, Ca., also surveying damage and collecting information.

Report #5

Post-Nisqually-Eathquake Investigations

Bucknam and Lidke, U. S. Geological Survey, Golden, CO., written communication.

Report #6:

Post-Nisqually-Eathquake Investigations

Alan Nelson, U. S. Geological Survey, Golden, CO., written communication.

Report #7

Dave Carver, Jack Odum, Tom Bice, and Chuck Mueller, U. S. Geological Survey, Golden, CO., in person discussion.

Our crew deployed 6 digital strong motion seismic recording stations in and around the Olympia, Washington area. One station was installed on bedrock, the others on sites that have been occupied in prior earthquakes investigations. After installing these instruments we moved our headquarters to Seattle and began collection of earthquake records from our 23 strong motion recorders in this area. All of our Seattle stations recorded the main event of February 28, 2001. 10:58am and all but one station recorded all the aftershocks. The data appears to be very good and will provide valuable information about this earthquake (Nisqually).