Deep 7.1 Quake Rattles Colombia; Dallas Suburb Rattled by 3.4-Magnitude Quake

Deep 7.1 Quake Rattles Colombia

September 30, 2012

AP - A powerful 7.1-magnitude earthquake centered nearly 100 miles underground rattled southwestern Colombia on Sunday but no damage or injuries were reported.

The quake struck at 11:31 a.m. local time 30 miles (48 kilometers) from the regional capital of Popayan and was felt in Bogota as well as 10 of Colombia's 32 states.

The U.S. Geological Survey said its epicenter was 94 miles (150 kilometers) beneath the earth's surface.

The quake was the most powerful to hit Colombia since a 7.2-magnitude temblor shook the same region in 2004, said Patricia Pedraza of Colombia's geological service.

Security chief Edith Cabeza of Cauca state, of which Popayan is the capital, said the "white city" of 270,000 inhabitants suffered no damage.

 Popayan's historical center was largely reconstructed after a March 1983 quake that killed at least 250 people.

3.4 Magnitude Quake Rattles Dallas, Texas, Suburb

September 30, 2012

AP - A minor earthquake and an aftershock minutes later rattled the western suburbs of Dallas overnight, but authorities reported no damages or injuries and a major airport close to the epicenter continued with normal flight operations.

An initial quake measuring a preliminary magnitude of 3.4 struck at 11:05 p.m. CDT Saturday and was centered about 2 miles north of the Dallas suburb of Irving, the US Geological Survey's national earthquake monitoring center in Golden, Colo., reported. USGS Geophysicist Randy Baldwin told The Associated Press from Colorado that the initial quake lasted several seconds and appeared strong enough to be felt up to 15 or 20 miles away.

He said a smaller aftershock at an estimated 3.1 magnitude occurred about four minutes later, just a few miles from the first temblor in an area west of Dallas.

The Colorado center's online reporting system received more than 1,200 online responses from people who felt the ground shudder. "Of all the reports we've received there were no intensities of a damaging nature. We haven't heard of any kind of damage and it's probably too small for that," Baldwin added.

Authorities in Irving said they were still checking their area early Sunday but had no immediate reports of any significant impact.

The Dallas-Fort Worth International Airport continued operations normally even as the quake surprised those at the airport partially located in Irving's city limits, airport public affairs officer David Magana said. He told AP said the airport, which bustles at peak hours because of 1,800 daily departures and arrivals, was in a quiet period with very little air traffic late Saturday night.

But he said those at the airport definitely felt the ground shake.

"I wouldn't call it panic. I would call it surprise," Magana said.

He said members of the airport operations team inspected landing strips, buildings and other airport installations but reported no damage.

"There were no impacts or outages and no disruptions to flights," Magana said. "I felt it at my house. It shook it a little bit but it wasn't enough of a jolt to shake anything loose like you have in California. I've been in California and this was nothing like that."

Some reports in Dallas said the rattling was felt for many blocks all around Irving, beginning lightly and ending with a jolt. One person reported the quake was strong enough to knock open some file cabinets.

Baldwin said more aftershocks are possible Sunday, noting the region has been periodically rattled by small quakes including a swarm of minor temblors in 2008. He also said preliminary magnitude estimates of the quake and aftershock could be revised after further study of the data because the seismological station is located about 65 miles from the initial epicenter, somewhat distant for precise readings.

Unusual Dallas Earthquakes Linked to Fracking, Expert Says

October 1, 2012

LiveScience.com - Three unusual earthquakes that shook a suburb west of Dallas over the weekend appear to be connected to the past disposal of wastewater from local hydraulic fracturing operations, a geophysicist who has studied earthquakes in the region says.

Preliminary data from the U.S. Geological Survey (USGS) show the first quake, a magnitude 3.4, hit at 11:05 p.m. CDT on Saturday a few miles southeast of the Dallas-Fort Worth (DFW) International Airport. It was followed 4 minutes later by a 3.1-magnitude aftershock that originated nearby.

A third, magnitude-2.1 quake trailed Saturday's rumbles by just under 24 hours, touching off at 10:41 p.m. CDT on Sunday from an epicenter a couple miles east of the first, according to the USGS. The tremors set off a volley of 911 calls, according to Reuters, but no injuries have been reported.

Not a coincidence

Before a series of small quakes on Halloween 2008, the Dallas area had never recorded a magnitude-3 earthquake, said Cliff Frohlich, associate director and senior research scientist at the University of Texas at Austin's Institute for Geophysics. USGS data show that, since then, it has felt at least one quake at or above a magnitude 3 every year except 2010.

Frohlich said he doesn't think it's a coincidence that an intensification in seismic activity in the Dallas area came the year after a pocket of ground just south of (and thousands of feet below) the DFW airport began to be inundated with wastewater from hydraulic fracturing.

During hydraulic fracturing, or "fracking," millions of gallons of high-pressure, chemical-laden water are pumped into an underground geologic formation (the Barnett Shale, in the case of northern Texas) to free up oil. But once fractures have been opened up in the rock and the water pressure is allowed to abate, internal pressure from the rock causes fracking fluids to rise back to the surface, becoming what the natural gas industry calls "flowback," according to the Environmental Protection Agency. 

"That's dirty water you have to get rid of," said Frohlich. "One way people do that is to pump it back into the ground."

In a study he recently published in the journal Proceedings of the National Academy of Sciences, Frohlich analyzed 67 earthquakes recorded between November 2009 and September 2011 in a 43.5-mile (70 kilometers) grid covering northern Texas' Barnett Shale formation. He found that all 24 of the earthquakes with the most reliably located epicenters originated within 2 miles (3.2 km) of one or more injection wells for wastewater disposal.

The injection well just south of DFW airport has been out of use since September 2011, according to Frohlich, but he says that doesn't rule it out as a cause of the weekend's quakes. He explained that, though water is no longer being added, lingering pressure differences from wastewater injection could still be contributing to the lubrication of long-stuck faults.

"Faults are everywhere. A lot of them are stuck, but if you pump water in there, it reduces friction and the fault slips a little," Frohlich told Life's Little Mysteries. "I can't prove that that's what happened, but it's a plausible explanation."

History of human-induced earthquakes

Oliver Boyd, a USGS seismologist and an adjunct professor of geophysics at the University of Memphis, agrees that, in general, links between wastewater injection and seismic activity are plausible.

"Most, if not all, geophysicists expect induced earthquakes to be more likely from wastewater injection rather than hydrofracking," Boyd wrote in an email to Life's Little Mysteries. "This is because the wastewater injection tends to occur at greater depth where earthquakes are more likely to nucleate. I also agree [with Frohlich] that induced earthquakes are likely to persist for some time (months to years) after wastewater injection has ceased."

For past examples of likely human-induced earthquakes, Boyd points to the story of the Rocky Mountain Arsenal, a now-closed U.S. Army chemical weapons manufacturing center that operated just outside of Denver until the early '90s.

In 1961, the Rocky Mountain Arsenal drilled a 12,000-foot-deep (3,658 meters) waste fluid disposal well near Denver. According to the USGS, "an unusual series of earthquakes erupted in the area soon after."

Use of the well was discontinued in February 1966. A year and a half later, on Aug. 9, 1967, a 5.3-magnitude earthquake, the most powerful in Denver's history, struck. It was followed by a 5.2-magnitude quake in the region that November, according to the USGS.