![]() As a result, it is not obvious how far earthquakes may occur from injection wells. There is a trade-off between decreasing effects from the well and increasing chances of triggering a fault. Of course, the pressure that a well exerts also decreases with distance. But at greater distances from the well, the number of faults that are affected rises, increasing the chance of encountering a fault that can be triggered. Because water does not need to be injected directly into the fault to generate earthquakes via poroelasticity, it can trigger them far away from the injection well.ĭeep disposal wells are typically less than a foot in diameter, so the chance of any individual well intersecting a fault that is ready to have an earthquake is quite small. More recently it has become clear that water injection can also cause earthquakes in other ways.įor example, water injected underground can create pressure that deforms the surrounding rock and pushes faults toward slipping in earthquakes. Since the 1970s, scientists and engineers have understood that injecting water directly into faults can jack the faults open, making it easier for them to slide in an earthquake. ![]() At first glance, one might expect that the most likely place for wastewater disposal to trigger an earthquake is at the site of the injection well, but this is not necessarily true. USGS Transmitting pressure through rockĪssessing how far from a well earthquakes might occur has practical consequences for regulation and management. We also found that, contradictory to conventional wisdom, injecting fluids into sedimentary rock rather than the harder underlying rock often generates larger and more distant earthquakes.Ĭumulative number of earthquakes with a magnitude of 3.0 or larger in the central and eastern United States, 1973-2015. We found that in some cases wells could trigger earthquakes up to 10 kilometers (6 miles) away. In collaboration with a researcher in my group, Thomas Goebel, I examined injection wells around the world to determine how the number of earthquakes changed with the distance from injection. But earthquake scientists like me want to anticipate how far from injection sites these quakes may occur. The timing of these earthquakes makes it clear that they are linked with deep wastewater injection. This process is responsible for a surge of earthquakes in Oklahoma and other regions. Enhanced oil recovery techniques, including dewatering and hydraulic fracturing, or fracking, have made accessible large quantities of oil and gas previously trapped underground, but often result in a glut of contaminated wastewater as a byproduct.Įnergy companies frequently inject wastewater deep underground to avoid polluting drinking water sources. Earthquakes in the central and eastern United States have increased dramatically in the last decade as a result of human activities.
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