When news broke of the seismic shaking that accompanied the 67-yard touchdown run by Marshawn Lynch of the Seattle Seahawks at Qwest Field on January 8, I thought back to the greater shaking that resulted from the Kingdome’s implosion. Two months after the implosion, Richard L. Hill of the Oregonian wrote a report on its seismic impact:
The implosion that recently crunched Seattle’s Kingdome is proving to be more than a 16.8-second spectator sport. The earth-shaking event also is part of a unique experiment giving scientists a clearer picture of the city’s earthquake risks.
Before the blast, researchers with the U.S. Geological Survey and the University of Washington placed more than 200 seismometers throughout Seattle. The detectors were spaced about every eight or nine blocks from Boeing Field to the south of the Kingdome to Green Lake in the north.
Treating the demolition as an earthquake, scientists are using the seismic waves detected by the instruments to study how the ground in parts of the city amplifies shaking and to develop a three-dimensional image of the geological structures near the Seattle Fault. Researchers are analyzing the data, with preliminary results expected by the end of the summer.
“The signal from the Kingdome implosion was much better than we had hoped for,” said William P. Steele, coordinator of UW’s seismology lab that monitors Northwest earthquakes.
Seismometers already in place to measure quakes detected the collapse from as far away as Olympia, about 60 miles south, and Mount Baker, about 85 miles north. It was the equivalent of about a magnitude 3.0 earthquake. Only people near the Kingdome felt the ground shake.
Rather than recording the explosion, the seismometers detected the shock waves produced by the collapse of the building — especially its 25,000-ton concrete roof.
It seems that the implosion was actually more like a 2.3 magnitude. The day after, the Seattle Post-Intelligencer wrote a report that in some ways sounds like a summary of damage from a minor quake:
The Kingdome took more than three years to build. Yesterday, it fell in 16.8 seconds.
And when the stadium – along with its 25,000-ton concrete roof – shuddered and crashed, the Earth literally moved.
Vibrations from the implosion, equal to a 2.3-magnitude earthquake, rippled through the Pioneer Square neighborhood. The sound of the blast traveled for miles, and some people said they felt concussions from far away.
Several windows of nearby buildings were blown out, which spelled opportunity for Brian Perkins, a fifth-generation glazier with Perkins Glass of Capitol Hill.
By noon, the company had replaced about 15 shattered windows in three buildings and was getting started on a fourth – the Salvation Army, east of the Dome on Fourth Avenue South.
A bigger nuisance was dust from the implosion. A giant cloud of fine white powder billowed north of the collapsed stadium and coated cars and streets in the International District. But shortly after the 8:32 a.m. implosion, crews spread into the streets to clean up the mess.
By the numbers
Duration, in seconds, of yesterday’s implosion : 16.8
Pounds of dynamite used: 4,461
Cubic feet of air, in millions, displaced by collapse: 68
Earthquake magnitude equivalent of implosion : 2.3
Seismometers hidden in back yards and buildings: more than 200
There’s a background note to the Kingdome seismic test: it was preceded by some forensic seismic work on the Oklahoma City federal building blast. The Seattle Times wrote:
“The benefit to us is that you never know ahead of time when an earthquake is going to happen,” said Thomas M. Brocher, a seismologist with the Geological Survey in Menlo Park, Calif. “So we treated the demolition like an earthquake to get a uniform sampling of how various neighborhoods are going to respond in a quake.”
The Kingdome blast wasn’t the first demolition that Brocher has examined. He was involved in studying the shock waves generated by the implosion of the shell of the nine-story Alfred P. Murrah Federal Building in Oklahoma City. A bomb a month earlier killed 169 people.
Brocher and his colleagues determined that only one blast, not two as some people initially thought, had destroyed the building. “The seismic waves generated by the criminal blast had been misinterpreted,” Brocher said. “The demolition helped us confirm that only one explosion had occurred.
“That experiment gave us confidence that we could get some useful signals out of the demolition of the Kingdome,” he said.
And, there’s a postscript: the World Trade Center attacks produced five different seismic events, which Columbia University recorded on this page. The two tower collapses registered 2.1 and 2.3 magnitudes. (By the way, earthquakes do happen in Manhattan: here’s one example only weeks after 9/11.)