The first one shook people awake. Then another shake about an hour later. Two earthquakes rattled Glenwood Springs early Tuesday morning. 

The first was a 3.4-magnitude quake recorded at 3:02 a.m. about 1.2 miles northwest of Glenwood Springs. 71 minutes later, a 3.6 magnitude quake was recorded nearby. 

We asked Dr. Harvey Benz, a scientist in charge of the U.S.Geological Survey National Earthquake Information Center to field some questions about earthquakes in Colorado.

First off, what's the National Earthquake Information Center?

“This is the one place within the federal government and within the world that is charged with monitoring the entire planet for earthquakes," Benz said. 

He said the NEIC monitors earthquakes worldwide down to about 4.5-magnitude and in the United States down to a 2.5-magnitude.

Each year, the NEIC monitors about 30,000 earthquakes all over the world.

How quickly does NEIC learn of earthquakes in Colorado?

Benz said it typically takes about 30 seconds to a minute and a half for the NEIC to learn of an earthquake in the U.S. For earthquakes outside the U.S., it can take anywhere from three to six minutes.

How common are earthquakes in Colorado?

The NEIC started recording good digital data back in 1973. Since then, Benz said Colorado recorded about 600 earthquakes.

“The most active area of Colorado in the last 40 years has been down in the Raton Basin,” he explained. “It’s a complicated area that involves tectonic earthquakes. It's on the northern end of the Rio Grande Rift, so we have active faults there."

Benz said it's also an area that has had oil extraction and wastewater disposal, "so there's a lot of induced earthquakes.”

What was the largest earthquake in Colorado?

Benz said them most recent, notably large earthquake occurred August 23, 2011. The 5.3 magnitude quake was recorded just southwest of Trinidad. 

"The largest analyzed earthquake was pre-20th century in the late 1880s," Benz said. "It was an earthquake that was estimated to be in magnitude 6-range."

Benz said there was no instrumentation to locate the earthquake, but it was believed to be west of Fort Collins.

What's the most common question about Colorado earthquakes?

“It’s always, ‘what’s the biggest earthquake we can have in Colorado?’ And I simply don’t know the answer to that," Benz said. "We can't predict when an earthquake can happen, but what we're really good at doing is being able to understand earthquakes, understand the ground-shaking from earthquakes and then use that in the building codes so that we can build communities that are resilient to earthquakes."