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Earthquake Swarm at Mount Hood, Oregon


Earthquake Hazard – Mount Hood,  Oregon

North-America – USA | State of Oregon, Mount Hood Volcano
Location: N 45° 22.407, W 121° 41.740  

Rumbling under the Volcanoes | May 17th, 2016

Hazards map for Mount Hood including likelihood of impact for proximal (close) and distal (farther) hazards zones and lahar travel times.  (Click image to view full size.)

Hazards map for Mount Hood including likelihood of impact for proximal (close) and distal (farther) hazards zones and lahar travel times. (Click image to view full size.) – USGS Volcano Hazards Program

More Information:

USGS:  Volcano Hazards Program

The Pacific Northwest Seismic Network (PNSN)

Earthquake in USA on Saturday, 29 March, 2014 at 05:09 (05:09 AM) UTC.

A swarm of little earthquakes has been rumbling this week beneath Mount Hood, Oregon’s tallest peak, but geologists said there is no cause for alarm. Sensors have recorded nearly 40 tremors near Government Camp, an unincorporated community in Clackamas County, since Sunday morning, with the largest a magnitude 2.3, barely big enough to feel. The 11,240-foot mountain is a mecca for skiers, hikers and climbers. It is also volcanic. But researchers say the recent quakes are normal activity and aren’t signs of volcanic activity, such as magma heating up and starting to flow beneath the mountain. “No one should start to batten down the hatches,” said Ian Madin, chief scientist with the Oregon Department of Geology and Mineral Industries. Mount Hood is in a chain of volcanic peaks, called the Cascade Range, stretching from Canada into California. The chain includes Mount St. Helens, just to the north of Mount Hood, which erupted violently in 1980 and last erupted in January 2008. Geologists say the recent quakes on Mount Hood appear to be caused by tectonic plates shifting, possibly along a nearby fault line deep in the earth, as the Cascades slowly stretch. It’s a process that has been happening over millions of years. Seismologist Seth Moran at the Cascades Volcano Observatory in Vancouver, Wash., said it’s not clear where exactly the quakes originated – they are small and deep, and there are not enough seismic stations in the area to pinpoint them – but he thinks most occurred near Government Camp. He said “bursty” swarms of small earthquakes under the mountain’s south flank are normal, but a large quake right under its peak or a sustained series of quakes that build in magnitude could be cause for alarm. The quakes this week fit within the broad category of what is normal in the region, Moran said. Little quakes like these give scientists a better understanding of what that “regular state of being” looks like, he said. They can then compare the “normal” against activity that may be a precursor of greater threats. Geologists say the last confirmed eruption of Mount Hood was more than 230 years ago, and it’s hard to predict when it will blow again. Any of the volcanoes in the Cascades could erupt again “in our lifetimes,” Moran said.


Media Headlines:

Earthquakes pose no threat to Government Camp, but seismologists watching closely

Via Oregon Live

GOVERNMENT CAMP — A series of small earthquakes that rumbled under Government Camp this week poses no threat to area residents, authorities said.

Seth Moran, seismologist for the U.S. Geological Survey at Cascades Volcanic Observatory, said that earthquake swarms like this weekend’s happen several times a year at Mount Hood.

“They can last days or weeks,” Moran said, adding the earthquakes are a result of the shifting of underground tectonic plates — not magma-related processes in Mount Hood, a dormant volcano.

More than 30 small earthquakes were recorded this past weekend, occurring three to four miles below ground.

Moran said that the largest earthquake under Mount Hood registered 4.5 on the Richter magnitude scale in July 2002.  By comparison, the largest earthquake this weekend registered a 2.3 and some were as small as 0.3.

Furthermore, the recent series of earthquakes has lasted only a few days.  Moran said one swarm on Mount Hood lasted a month.

“The point being there have been plenty of larger earthquakes at Mount Hood than we’ve seen with these,” Moran said. “In contrast to that, this is not that big of a deal.”

Some residents may or may not have felt the vibrations, but Deputy Chief John Ingrao of the Hoodland Fire District said no one has called the fire station about them.

“Usually when there’s some seismic activity on the mountain, we will have residents call us,” Ingrao said. “We have not had a single call.”

Moran said that it’s possible a “very sensitive person could have felt the earthquakes” because of Government Camp’s proximity to the quakes.

–Byron Wilkes

Geologists record 38 small quakes on Mt. Hood since Sunday

by Keely Chalmers, KGW News

A swarm of small earthquakes on Mount Hood has captured the attention of state geologists and rattled the nerves of some nearby residents.

The quakes started Sunday evening and have been rumbling directly beneath Government Camp.

… As of Friday geologists have recorded 38 tremors. The largest one was only a magnitude 2.3, barely big enough to feel.

But it’s not the size of the quakes that’s intriguing the scientists, it’s where they’re happening. They seem to be occurring right alongside a recently discovered fault.

“The fact that the earthquakes are defining a fault means that that fault is active and if it can make a magnitude 2.3 it can probably make a much larger earthquake,” explained Ian Madin Chief Scientist with the Oregon Department of Geology and Mineral Industries.

Madin has been tracking this swarm since it began.

Unlike past seismic swarms on Mount Hood, he said this one is likely not tied to any volcanic activity.

And he does not think the quakes are a pre-cursor to a future eruption.

But he explained now that geologists know there may be active fault close to Government Camp, they can keep a closer eye on it.

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