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Shifting plates cause of Hoods quakes

State geologist says group of tremors nothing to fear


Mount Hood’s cluster of earthquakes last week caused concern in surrounding villages.

But the earthquakes were simply the mountain doing what it normally does, and are no reasons to be concerned, said state geologist Vicki McConnell of the Oregon Department of Geology and Mineral Studies.

“The pattern indicates that they are tectonic earthquakes, due to shifts in the earth’s crust,” McConnell said. “They’re not of the seismic magnitude that would indicate volcanic activity.”

Over the course of several days, the mountain experienced more than 30 small earthquakes, mostly centered on the Government Camp area, although most were not even strong enough to be felt.

Of the 20 most recent earthquakes, Pacific Northwest Seismic Network measured the largest at 2.3 on the Richter scale; it occurred at 9:23 a.m. Monday, March 24.

The last of the group of earthquakes was recorded at 5:13 a.m. Thursday, March 27. It registered at only 0.8.

Seismologists use the Richter scale to measure the energy released during an earthquake.

McConnell described last week’s seismic event as an earthquake swarm, a cluster of earthquakes that occur close together in a relatively short amount of time. Mount Hood experiences hundreds of earthquakes a year, and around two to three earthquake swarms, McConnell said.

McConnell suggests checking Pacific Northwest Seismic Network for information on earthquakes occurring near Mount Hood. The network is dedicated to providing fast and accurate information about local earthquakes in the region. Seismologists and volcanologists can use that information to determine if the activity is cause for concern. “It’s great that we have this,” McConnell said.

So far, nothing has been found to indicate there may be any more, bigger earthquakes coming our way. McConnell said if experts had found any troubling evidence in the recent earthquake swarm, they would have known already.

Pacific Northwest Seismic Network data shows a grouping of recent earthquakes around Government Camp that form a line, which could indicate a fault line for a tectonic plate.

McConnell said the most likely cause for the earthquake swarm is a local fault line, but there have not been any faults specifically mapped.

Data from the network can be found at http://www.pnsn.org/volcanoes/mount-hood#recent-seismicity.