Tremor near Lake Spokane likely micro earthquake

A micro earthquake was reported Wednesday in the vicinity of Lake Spokane to the southwest of Tum Tum, according to the Pacific Northwest Seismic Network. The quake measured 1.7 in magnitude based on the duration of the shaking and occurred at 7:50 p.m. Wednesday at an estimated depth of 0.3 miles below the surface. The location was 12 miles north-northeast of Reardan. There were no reports of the earthquake being felt. Minor quakes occur frequently across the Columbia Basin and northern mountains of Northeast Washington and are sometimes concentrated in one locale. In 2001, a swarm of dozens of minor earthquakes rattled north Spokane. Earthquake swarms have also occurred near Maupin, Ore., in 2007 and 2008 and near Wooded Island just north of Richland on the Columbia River in 2009. The Wooded Island swarm produced 750 earthquakes no larger than magnitude 4. Amy Wright, a seismic analyst for the network, confirmed that the small Lake Spokane tremor on Wednesday was likely an earthquake rather than a landslide or an error in the seismic measuring network. The seismic activity may be the result of a small but steady north-south compression within the Columbia River basalts, which make up the top layers of the earth’s crust across the region, seismologists said. Larger earthquakes in these layers are considered unlikely. “These swarms are not indicators of large earthquakes in the near future,” according to the PNSN Web site at geophys.washington.edu/SEIS/PNSN/.