Photo Credit: Brian Sherrod, USGS. Creative Commons License 2.0, via flickr. https://flic.kr/p/r6Wt76
What’s behind the sudden surge in earthquakes in the middle of the United States?
Human-induced earthquakes. I’m Bob Hirshon and this is Science Update.
Geologists now agree that human activities have caused the dramatic increase in earthquakes in Oklahoma and many other states. Geologist Danielle Sumy at the Incorporated Research Institutions for Seismology or IRIS, explains that conventional oil drilling brings up large amounts of salt water along with the petroleum. Companies dispose of that water by injecting it deep underground. The problem is, most oil drilling is done near faults.
To have a petroleum “play,” or an area that is going to have oil and gas, you actually need a structural barrier, like a fault, to be able to trap the oil and gas.
Under certain conditions, wastewater injection can trigger earthquakes in these faults. A new report by the USGS claims that while fluid from hydraulic fracking is a contributor, the main culprit is the greater volumes of water from conventional drilling. I’m Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
For some time now, researchers and laypeople have been wondering if there is a link between the extraction of fossil fuels like oil and natural gas and earthquakes. Much of this speculation is due to the fact that states like Oklahoma are experiencing more earthquakes than they had in the past. In fact, Oklahoma has been rocked by more magnitude-3 quakes than California, the most seismically active of the lower 48 states, according to Mark Petersen, who leads the U.S. Geological Survey's national mapping project. This survey also found that earthquakes are hundreds of times more common in Oklahoma than they were until a few years ago.
Geologists have set out to investigate what could be causing this increase in seismic activity in the Midwest because Oklahoma isn't the only state that has experienced this phenomenon. States like Alabama, Arkansas, Colorado, Kansas, New Mexico, Ohio, and Texas have all experienced quakes in once-stable regions.
The researchers involved in this survey conducted it by mapping seismic activity in relation to the location of extraction sites. They found that all of the newly earthquake-prone areas were located near deep fluid-injection wells. Fluid-injection wells are used as part of oil drilling and fracking, which is the process of drilling down into the earth before a high-pressure water mixture is directed at the rock to release the gas inside. Water, sand, and chemicals are injected into the rock at high pressure, which allows the gas to flow out to the head of the well. Both processes usually have a lot of wastewater left over. This wastewater is then disposed of by injection into deep wells.
The injection of wastewater into the deep wells has the effect of loosening the faults, which are divisions in the rocks that make up the Earth's crust. This process can lead to more earthquakes in a given area.
In order to try to deal with the potential threat from these extraction activities, the U.S. Geological Survey developed a preliminary set of models to forecast how hazardous ground shaking could be in the areas where sharp increases in seismicity have been recorded. The models ultimately aim to calculate how often earthquakes are expected to occur in the next year and how hard the ground will likely shake as a result. It is hoped that these models will help overcome the challenges in assessing seismic hazards in these regions in order to help keep communities safe from earthquakes.
Now try and answer these questions:
- How much more likely are earthquakes in Oklahoma now than just a few years ago?
- What other states are experiencing more seismic activity?
- How did the researchers conduct their survey?
- What are fluid-injection wells? What are they used for?
- What is fracking?
- What is one potential effect of injecting wastewater from fracking into deep wells?
To learn more about how difficult it is for scientists to understand how cracks in rocks and other mateirals operate, listen to the Crack Dynamics Science Update.
You can read more about this report in the New York Times article, U.S. Maps Pinpoint Earthquakes Linked to Quest for Oil and Gas.
Earthquakes and other natural disasters are important learning opportunities for your students. Natural disasters can be talked about at any time of the year and they can be used to address learning goals about how some changes in the earth's surface are abrupt (such as earthquakes and volcanic eruptions) while other changes happen very slowly (such as uplift and wearing down of mountains).
To extend the learning of this Science Update, you can use the Related Resources listed here or you can show your students The Science of Earthquakes, from the USGS.
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