In December of 1872, an earthquake shook the Pacific Northwest so hard that a Seattle resident described watching near-tidal waves roil Lake Union.
And it wasn’t just Seattle; the quake shook from Eugene, Oregon to Canada. It triggered a landslide near Wenatchee that briefly dammed the Columbia River.
For years, geologists couldn't pin down the quake's source. But now they think they've found it: A previously unknown fault near Entiat on the east side of the Cascades.
"So we had this big earthquake but no one could put their finger on where's the fault that's responsible," said Brian Sherrod, a paleoseismologist with the US Geological Survey.
A paleoseismologist studies ancient earthquakes. Sherrod said the source of the massive quake has baffled scientists for decades. Guesses placed the epicenter everywhere from Sedro-Woolley to Lake Chelan to British Columbia.
But not long ago, Sherrod and his team found a crack in the earth on a hillside near Entiat. Subsequent research dated trees, charcoal and other nearby material. It indicates that the crack is very likely a scar left from the 1872 quake.
Sherrod says it’s important to know. First, 143 years is an eye-blink in geological terms; what was active then could remain so. Also, the newly discovered fault shows how little we still know about seismic hazards in the northwest.
"We are just starting to find where the active faults are, and I mean just. We didn't even know where the Seattle fault was up until the early 1990s," he said.
Sherrod presented his findings last week at the annual meeting of the Seismological Society of America.
