March 22, 2000
Kingdome implosion could give greater understanding of Seattle Fault
Since the discovery of the Seattle Fault in the early 1990s, many people have worried how the region’s most-recognizable sports stadium would fare in a major earthquake. Now scientists hope the planned destruction of the Kingdome will give them a better picture of the fault and its associated risks to downtown Seattle.
Researchers with the U.S. Geological Survey and the University of Washington Geophysics Program plan to install more than 200 seismometers from the southern border of the city to just north of Green Lake to record shock waves from Sunday’s dome implosion. The detectors will be spaced about one-sixth of a mile apart on the property of volunteers.
On the day of the implosion, the USGS first plans to set off four early-morning detonations in deep boreholes, two in areas south of the dome and two to the north. The waves generated will be recorded by the seismometer array in place to document the dome’s destruction.
The Kingdome experiment is the third phase of Seismic Hazards Investigation in Puget Sound, or SHIPS, a project in which scientists are trying to better understand earthquake hazards in the region.
The charges being used on Sunday will be half as powerful as those used last fall by the USGS in another phase of the SHIPS experiment, but they might be felt mildly in some areas of the city, said Bill Steele, UW Seismology Laboratory coordinator. The lab will be staffed in the early morning hours for anyone who feels the detonations and wants to ask questions. The number is (206) 685-8180.
The Kingdome implosion is scheduled for 8:32 a.m. Sunday. The array of seismic monitors won’t record the explosion itself but rather the crashing of thousands of tons of concrete.
“It’s the falling of the roof to the ground that’s really going to send out shock waves,” Steele said.
Razing the dome to make way for a new football stadium for the Seattle Seahawks presents an ideal opportunity for seismologists to learn more about the Seattle Fault in an area where their information is the sketchiest, said Thomas Brocher of the U.S. Geological Survey in Menlo Park, Calif., director of the SHIPS experiment.
The Seattle fault runs from Bainbridge Island across Puget Sound to an area near the dome, then roughly follows the path of Interstate 90 to the Cascade foothills.
Scientists have clear images of the fault to the west and east of downtown Seattle, Brocher said. However, the presence of large structures and continuous construction disturbances have left them with only a hazy idea of the fault’s characteristics – including its precise location – in the downtown area, where the risk from substantial earthquake damage is perhaps the greatest. The fault is believed to pass about five blocks south of the dome.
Recording the shock waves from the dome’s demolition will allow scientists to study how the ground in various parts of the city amplifies the shaking and to develop a three-dimensional image of the rocks and geological structures within and near the Seattle Fault. The information will add to what already has been learned in the first two phases of the SHIPS experiment.
“We’re not 100 percent sure that the vibrations from the Kingdome demolition will give us useful information, but we’re pretty confident that it will, and the location of the Kingdome is too good an opportunity for us to pass up,” Brocher said.
In the first phase of SHIPS, air guns were fired into Puget Sound from the UW research vessel Thomas G. Thompson and the resulting seismic waves were recorded. Scientists gained knowledge of the geometry and location of the Seattle fault, and about the newly recognized Tacoma Narrows fault near Tacoma.
Preliminary findings suggest the Tacoma Narrows fault is a major geologic structure that could account for observations of rapid 10-foot rise of marsh deposits about 900 A.D., Brocher said. That fault will be the target of future studies to determine whether it is an active earthquake fault and, if so, to determine its history of large earthquakes.
The second phase of SHIPS recorded seismic waves from detonations in deep boreholes sunk at 2- to 3-mile intervals from Olympic National Park to the Cascades. Six detonations were set off in Seattle to study the Seattle basin, a depression filled with sedimentary rocks prone to shake harder than bedrock. The basin lies under Seattle north of the Seattle fault. Brocher said the information from Dry SHIPS “is already yielding important information about major geologic structures east of Seattle.”
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For more information, contact Steele at (206) 685-2255 or bill@geophys.washington.edu; or Brocher at (650) 329-4737 or brocher@andreas.wr.usgs.gov; or Craig Weaver, U.S. Geological Survey, Seattle, at (206) 553-0627 or craig@geophys.washington.edu.
NOTE: A news conference involving scientists from the University of Washington and the U.S. Geological Survey will be held at 10 a.m. Friday (March 24) at the SHIPS Experiment Staging Area, Building 32 of NOAA’s Sandpoint facility, 7600 Sandpoint Way N.E. in Seattle. The scientists will discuss the Kingdome implosion phase of the SHIPS experiment and announce new findings from the first two phases of SHIPS.
