Research geologists have just finished a field trial to test a less invasive way to complete seismic hazard surveys.
The federal scientists attempted to map an earthquake fault under Seattle simply by listening for underground echoes from all the noise we humans create at the surface.
Historically researchers have listened for seismic hazards by having a specialized "thumper" truck pound the earth to generate vibrations. Sound waves bounce off rock layers and folds underground. The reflections can tell scientists where a fault line runs or how much a neighborhood could shake in an earthquake.
U.S. Geological Survey research geologist Jack Odum found himself wondering if listening for the echoes of ambient noise in the city could be as revealing.
"If you stand on a street corner and a large construction truck or a garbage truck goes down the street, you'd notice the ground is moving just by that truck going by," Odum said.
So this month, Odem co-led a team that surveyed a worrisome earthquake fault in the Seattle area using just the echoes of passing traffic, airplanes, waves and other city noise.
"Preliminary results look like it is promising that we will be able to get some kind of imaging of the soil and rock structure," he said.
But there's a drawback, Odum added, because this method requires much more time on location.
A flier distributed by USGS in the two neighborhoods where the scientists patiently waited beside their sensor arrays said that if the new methodology is successful, it will allow the agency to extend its imaging surveys into locations where vibration trucks are unwelcome or cannot drive.
"In addition, this new approach potentially will have less impact on both local residents and environmentally sensitive areas such as parklands and roadless areas," the brochure said.
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