Some Vail Valley residents felt small earthquakes that hit Glenwood Springs
What’s the Richter scale?
The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.
Source: U.S. Geological Survey
EAGLE COUNTY — A pair of small earthquakes just north of Glenwood Springs were recorded in the early-morning hours of Tuesday, Dec. 11.
According to the Glenwood Post Independent, the first quake, about 1 mile north of Glenwood Springs, was recorded at 3:02 a.m. and had a magnitude of 3.4. The second, which was recorded at 4:13 a.m., was located about 3.7 miles north of town. That quake registered at 3.6 on the Richter scale. Both are considered mild quakes, but the rumblings were felt as far east as Edwards.
Small earthquakes are fairly common throughout the Rocky Mountains.
In an email, Colorado Geographic Survey Assistant Director Matt Morgan wrote that earthquakes occur along fault lines in the Earth. When those fault lines move against each other in a big way, you can get mountains. Colorado’s mountains were formed by that massive movement of plates against each other. But smaller movements happen all the time.
“The Earth is in a constant state of flux,” Morgan wrote.
While geologists and seismologists have mapped many fault lines in Colorado, “we do not know where all of them are,” Morgan wrote.
But, he added, there are mapped fault lines around Glenwood Springs, so small earthquakes can be expected from time to time. Morgan wrote that small quakes aren’t necessarily harbingers of bigger tremors to come.
“Making these types of predictions with limited data is difficult, if not impossible,” he wrote.
And earthquake activity, even substantial quakes like the one that recently hit Alaska — which was many times stronger than those recorded near Glenwood — usually are just earthquakes.
There’s a dormant volcano just north of Dotsero — the remains of the lava flow can be seen on either side of Interstate 70 in the area. Scientists believe the Dotsero volcano last erupted roughly 4,150 years ago. Morgan wrote that long-ago eruption was “pretty small” compared to most volcanoes. And, he added, the magma chamber beneath the volcano is no longer active.
With all that in mind, Morgan wrote that even large earthquakes rarely trigger volcanic events. Small quakes can occur around volcanoes. In an active zone such as Yellowstone National Park, fluids can migrate through the Earth’s crust and change pressure in the surrounding rocks, causing small earthquakes.
But, Morgan wrote, earthquakes and volcanoes are largely separate phenomena.
According to information on the U.S. Geological Survey, a large earthquake in Hawaii in 1975 triggered a relatively small eruption from the nearby Kilauea volcano. But that earthquake was a robust 7.2 magnitude quake.
Compared to the tremors that hit north of Glenwood, that 1975 quake was roughly 40 times stronger, and released more than 120 times the energy.
Officials are able to closely track earthquakes all across the globe. Morgan wrote that the Colorado Geological Survey operates eight seismometers around the state. Data from those devices is sent to the U.S. Geological Survey’s office in Golden. Officials plan to install three more seismometers over the next two years.
The data and research — including placing trenches along known fault lines — is used to study fault lines and get a better understanding of earthquake behavior. State scientists aim to answer questions including:
• When was this fault last active?
• How many events occurred, and over what time period?
• Does this fault pose a hazard to a populated area?
While scientists work to learn more about earthquakes in Colorado and around the globe, one thing is certain: Every once in a while, the Earth will move, but will do little, if any, damage.
Vail Daily Business Editor Scott N. Miller can be reached at email@example.com and 970-748-2930. Glenwood Springs Post Independent Editor John Stroud contributed to this story.
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