KGOU

Recent Swarm of Earthquakes Likely To Be Aftershocks, Not Signs Of Future Quakes

Sep 21, 2017

State and federal scientists say that recent earthquakes in two Oklahoma cities are probably aftershocks, rather than indications of larger quakes to come.

Sarah Terry-Cobo writes in the Journal Record:

A magnitude 5 quake struck Cushing in November, and there have been 27 aftershocks since then, according to the Oklahoma Geological Survey. Six of those aftershocks were magnitude 3 or stronger, three of which have happened in the last two weeks. A magnitude 4.2 hit Stroud July 14, about 20 miles south of Cushing. Six aftershocks have hit Stroud since then, including a magnitude 3.9 recorded Saturday.

Researchers are still watching the area closely in case of cumulative damage from the repeated quakes. Cushing is home to the country’s largest storage hub for crude oil.

Despite the recent swarm, Oklahoma has seen fewer quakes in the past two years.  One cause could be a decrease in wastewater from oil drilling.

Speaking to KGOU’s Nomin Ujiyediin, Terry-Cobo said, “The Oklahoma Corporation Commission—that’s the oil regulatory agency—they have put some restrictions and shut down some wells near some of the quakes. That has helped, in part, to have less wastewater putting pressure on those faults underground. Another thing is less oil and gas production. When oil prices crashed in late 2014 and were pretty unstable in 2015, people drilled and pumped less, so there was less wastewater."

FULL TRANSCRIPT

Nomin Ujiyediin: This is the Business Intelligence Report, a weekly conversation about business news in Oklahoma. I'm Nomin Ujiyediin, filling in for Jacob McCleland. I'm here today with Journal Record reporter Sarah Terry-Cobo. Thanks for joining us, Sarah.

Sarah Terry-Cobo: Thanks for having me.

Ujiyediin: Let's talk about your earthquake story that was published in The Journal record yesterday. Tell me what's been happening in Cushing and Stroud.

Terry-Cobo: Well, essentially, we are looking at earthquakes near Cushing and near Stroud. There have been a few dozen after the big Cushing quake last November, several of which have been felt in recent weeks. And then there have been several near Stroud.

Ujiyediin: What makes Oklahoma's earthquakes different from quakes in other places like California?

Terry-Cobo: Well, there's a few things but probably the most notable one is that the majority of California quakes are considered natural. And that's from two giant plates smashing into one another, one of them sliding underneath the other—those are fault lines. In Oklahoma, many are linked to wastewater that's disposed of from oil and gas production. So these are so-called “triggered” or “induced” earthquakes in Oklahoma, and they are much shallower than the natural ones in California. So the Oklahoma earthquakes can be felt much further.

Ujiyediin: In your story you talk about aftershocks and foreshocks. What’s the difference between them?

Terry-Cobo: So, like the name suggests, aftershocks are weaker quakes that happen on the same fault over a period of time after the main shock, or the big one. And foreshocks come before. So some of the large quakes in Oklahoma—the magnitude fours and the fives—those have been preceded in many cases by clusters of small foreshocks. So I was interested to find out if what they're feeling in Cushing or in Stroud are foreshocks, or you know, an indication of a stronger one, or just aftershocks. And so far, scientists think these recent swarms in both places behave like aftershocks

Ujiyediin: Oklahoma's earthquake rates have actually declined in the past couple of years. Can you talk about why that is?

Terry-Cobo: Well, there's a couple of reasons. And one is that the Oklahoma Corporation Commission—that’s the oil regulatory agency—they have put some restrictions and shut down some wells near some of the quakes. That has helped, in part, to have less wastewater putting pressure on those faults underground. Another thing is less oil and gas production. When oil prices crashed in late 2014 and were pretty unstable in 2015, people drilled and pumped less, so there was less wastewater.

Ujiyediin: Is there anything else that can be done to reduce or predict earthquakes? What are researchers looking to do in the future?

Terry-Cobo: Well you can't really predict earthquakes but like the weather, scientists can forecast the probability of what they think will happen, and that's based on measurements and computer models, that sort of thing. The Oklahoma Geological Survey staff want to be able to dedicate a single person to digging into those details of the smaller quake swarms. And where those smaller quake swarms are compared to those underground faults. That sort of stuff could help develop a short-term forecast—but they're limited in staff. So they've already asked for more funding, grant funding for another post-doctoral student to just be dedicated to that, just to study that.

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