More than 100 small earthquakes have been recorded since Saturday on the edge of the Hanford Reach National Monument, according to the Pacific Northwest Seismic Network.
The quakes were at the western edge of the monument’s McGee Ranch, the land used as a security perimeter around the nuclear reservation during the years it produced plutonium for the nation’s nuclear weapons program.
“This is a completely natural phenomenon; although this swarm happens just outside the Hanford site, is has nothing to do with the radioactive waste stored there,” according to a blog post from the seismic network, a University of Washington and University of Oregon program to monitor earthquake and volcanic activity across the Pacific Northwest.
As of Tuesday, the seismic network put the number of earthquakes in recent days at about 100, but with some of the smallest likely missed and others not analyzed yet. On Wednesday, Doug Gibbons, a research engineer for the network, put the number at 115.
No reports of the earthquakes being felt had been reported to the network as of Wednesday morning.
That is to be expected, both because of the remote location and because the quakes were small, Gibbons said.
According to a map posted by the network, most were below a magnitude 2.0. The largest may have been a magnitude 2.9 on the north end of the swarm at 8:22 p.m. Sunday.
To be widely felt, earthquakes have to be at least about magnitude 3.5, Gibbons said.
The earthquakes were relatively shallow, he said.
Earthquakes in Western Washington may be 30 to 40 miles deep. But these were mostly around 5 miles deep.
Scientists consider them a swarm because there was no clear main shock and only a short time between events, according to a Wednesday blog post by Renate Hartog, manager of the Pacific Northwest Seismic Network.
