What's Oklahoma's Earthquake Number?

Thursday, May 10th 2012, 2:12 pm
By: News 9

We're in the heart of tornado alley. But lately, Oklahoma's also been home to a large number of earthquakes. Just about all of us felt Oklahoma's largest ever recorded earthquake in November 2011.

But unless you lived near the epicenter in Prague, chances are you didn't have any damage. With so much seismic activity in the sooner state in the past few years, we wanted to know,  what magnitude earthquake would be too much for Oklahoma's red dirt to handle?  Seismologist Austin Holland has his theory.

"A magnitude 7 earthquake will have widespread damage and quite a bit of catastrophic failure in older buildings," Holland said.

The San Francisco bay area is all too familiar with earthquake destruction. I traveled to San Francisco and asked David Schwartz with the U.S. Geological Survey what's done to keep buildings standing.

Schwartz said bolts and external bracing are added to some buildings.

John Osteraas assesses the safety and damage of buildings after earthquakes all around the world. He was even called to Oklahoma City days after the Murrah bombing.

"When they evacuated everybody else, I went in to make sure everything was okay," Osteraas said about his time in Oklahoma City.

But he said if a strong earthquake shook Oklahoma City, he wouldn't want to be inside one of our buildings.

"In a strong earthquake, a lot of the unreinforced masonry buildings, perhaps some of the precast buildings, will not perform so well and I would expect to see some failures in those buildings," Osteraas said.

But while most of the structures in San Francisco, even the older ones, like the Golden Gate Bridge, were built to withstand earthquakes, those in Oklahoma City weren't.

Oklahoma City plan review supervisor Jeff Heinze said every new building must meet seismic code. But there isn't an inspector to make sure they're earthquake ready. The architect signs and seals the plans, promising they've met code.

"When they sign and seal plans, they put their credibility on the line, their license and their liability," Heinze said.

Devon officials tell us the Tower exceeds current seismic code and was built that way mostly for our high winds. But most of Oklahoma City's other high rises were built before we knew earthquakes were such a threat. Osteraas said it's not the skyscrapers we should worry about.

"For earthquakes in Oklahoma, we'd expect to see the higher frequency vibration, which is going to effect low to mid-rise buildings, maybe 8-10 stories," Osteraas said. "Once you get above that, the building is flexible. It really doesn't feel the vibration."

And all our experts believe that magical 7 magnitude quake is a long ways off from the sooner state.

"The largest events are very unlikely events," Holland said. "They're much less likely than the threes."

Osteraas agreed, "I don't think people in Oklahoma should fret about the big one."

Austin Holland said there are several factors that come into play to determine how much damage an earthquake can cause:

* Distance from the epicenter
* Age and design of structures
* And the soil and foundation under a building