Map could help pinpoint 1872 quake

CHELAN, Wash. – Scientists say new technology could solve one of the greatest earthquake mysteries in Washington state: The epicenter location of the 1872 quake that shook north-central Washington’s foundation.

At an estimated magnitude of 6.8, it is Eastern Washington’s biggest known earthquake. It spurred a landslide north of Entiat that temporarily blocked the Columbia River, caused damage as far away as Puget Sound, and was felt in British Columbia, Oregon and Montana.

If the U.S. Geological Survey gets a bigger budget next year, geologists in the Pacific Northwest hope to search for the point where that great quake originated, now believed to be in the area between Entiat and the south end of Lake Chelan.

Craig Weaver, USGS director for the Pacific Northwest, said the federal agency may get a slight increase in funding, and if this region gets some of it, the first thing he’ll do is use relatively new technology to get a high resolution topographic map of that area.

Developed in about 2000, LIDAR, or Light Detection and Ranging, uses lasers to scan the earth from a plane or helicopter and create a detailed ground map that ignores vegetation and structures.

Weaver said geologists would use the map to detect evidence left behind by the 1872 earthquake. They’d also look for other evidence of earth movements over the last 15,000 to 20,000 years. Then they’d go to the field for an on-the-ground investigation.

The technique has been used in Western Washington to locate big fault zones, Weaver said. He said he wants to do the same thing on Toppenish Ridge in Yakima County, where major fault lines are already known.

Others are excited by the prospect.

“It would really be great to find the so-called smoking gun, the fault zone, on the ground, and say, ‘Here is where that earthquake was centered,’ ” said Steve Malone, geophysics professor at the University of Washington’s Department of Earth & Space Sciences.

Malone said several studies and field investigations including one he conducted with his students have tried to pinpoint the spot, but none has succeeded.

They don’t want the information just for historical purposes.

“We want to understand why that large of a quake could have occurred there,” he explained.

Depending on what they find, the precise location could help detect features that make for similar-sized earthquakes in other areas.

Malone said the Lake Chelan-Entiat zone is one of the most active in Eastern Washington. Since 1975, UW’s Pacific Northwest Seismic Network has recorded about 2,000 earthquakes in the area, most of them small, but 43 of them large enough to be felt.

The largest was on April 10, 1984, at a magnitude of 4.3, he said.

“By recording small earthquakes, we do get a general sense of the likelihood of a larger earthquake,” he explained.

“We have a general knowledge that, if there are so many smaller earthquakes in an area, there’s likely to be a larger one. If, over 100 years, you have 100 magnitude 3 earthquakes, the chances are you’ll have 10 magnitude 4s and one magnitude 5,” he said.

But even more important than predicting when another big quake could occur, scientists hope to find a link between Eastern and Western Washington earthquakes by following fault lines, which could help them predict where a big earthquake is more likely to strike, even if they don’t know when.

That kind of information is useful for emergency responders who want to be prepared for the big one.

Dave Nelson, earthquake program coordinator for the Washington state Emergency Management Department, said his agency hosted a workshop in Yakima earlier this fall, inviting emergency responders from around Central Washington.

“We had kind of ignored Eastern Washington. We’ve kind of focused on the coast for the last couple of years because of the tsunamis and the Seattle Fault earthquakes. It was time to get some public education and tell people, ‘Say, this really could happen over here,’ ” he said.

Gene Yow, Chelan County PUD’s principal civil engineer, said he attended to hear the latest information on earthquakes in Eastern Washington. He said the Chelan County PUD, along with Grant and Douglas County PUDs, are working on a seismic hazard analysis.

“We’re confident on the one hand that our dams are designed appropriately. On the other hand, we want to be sure we stay abreast of whatever is developing in that field,” he said.

Weaver said more study in Eastern Washington could reveal a connection between earthquakes that occur east and west of the Cascade Range. Studies in Western Washington are indicating larger and more active faults than previously suspected, he said.

“I think as we come to appreciate how big these are, most of us think these are going to connect up to big faults in Eastern Washington,” he said. “We’re excited about coming up with a better model of how earthquakes work all over Washington state.”