EWU geologist measures ‘Bloomsquake’

The pounding feet of thousands of Bloomsday runners aren’t enough to cause an earthquake. But their motion does register on a seismometer, a device geologists use to measure the waves generated by earthquakes, volcanic eruptions and other geologic events.

The Spokesman-Review asked Chad Pritchard, assistant professor of geology at Eastern Washington University, to measure the “Bloomsquake” activity at the starting line Sunday morning. His machine – the size of a small block of ice – was on the ground on Riverside Avenue just before Monroe Street.

The seismometer recorded peaks in ground waves as each heat of runners took off. The early Yellow and Green groups caused the biggest spikes.

“You can see that the first people are running – they probably have more of a force,” Pritchard said. Later groups with more walkers generated smaller peaks in ground waves, as did the small group of elite runners.

“You could say that their excitement is recorded. I don’t know if that’s very scientific,” he said.

Though it’s possible to measure ground waves, calculating an actual magnitude for a surface event like Bloomsday is difficult.

Geologists typically have multiple seismometers at multiple locations to measure earthquake force, Pritchard said. The motion of thousands of feet hitting the ground at slightly different times is also different than an earthquake, where seismic waves radiate from a single point inside the earth.

Challenges like that prevented the Pacific Northwest Seismic Network from calculating a magnitude for “ Beast Quake,” the energy generated by thousands of Seahawks fans stomping their feet at Qwest Field.

“They can’t give you a magnitude for that. We’re just as cool as people in Seattle,” Pritchard said.