Injecting Wastewater Underground Can Cause Earthquakes Up to 10 Kilometers Away
By Emily Brodsky
Earthquakes in the central and eastern U.S. have increased dramatically in the last decade as a result of human activities. 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.
Energy companies frequently inject wastewater deep underground to avoid polluting drinking water sources. This process is responsible for a surge of earthquakes in Oklahoma and other regions.
The timing of these earthquakes makes it clear that they are linked with deep wastewater injection. But earthquake scientists like me want to anticipate how far from injection sites these quakes may occur.
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. We found that in some cases wells could trigger earthquakes up to 10 kilometers (6 miles) away. 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.
Cumulative number of earthquakes with a magnitude of 3.0 or larger in the central and eastern United States, 1973-2015.USGS
Transmitting Pressure Through Rock
Assessing how far from a well earthquakes might occur has practical consequences for regulation and management. 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.
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. More recently it has become clear that water injection can also cause earthquakes in other ways.
For example, water injected underground can create pressure that deforms the surrounding rock and pushes faults toward slipping in earthquakes. This effect is called poroelasticity. 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.
Deep 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. 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.
Of course, the pressure that a well exerts also decreases with distance. There is a trade-off between decreasing effects from the well and increasing chances of triggering a fault. As a result, it is not obvious how far earthquakes may occur from injection wells.
Where to Inject?
To assess this question, we examined sites around around the world that were well-isolated from other injection sites, so that earthquakes could clearly be associated with a specific well and project. We focused on around 20 sites that had publicly accessible, high-quality data, including accurate earthquake locations.
We found that these sites fell into two categories, depending on the injection strategy used. For context, oil and gas deposits form in basins. As layers of sediments gradually accumulate, any organic materials trapped in these layers are compressed, heated and eventually converted into fossil fuels. Energy companies may inject wastewater either into the sedimentary rocks that fill oil and gas basins, or into older, harder underlying basement rock.
At sites we examined, injecting water into sedimentary rocks generated a gradually decaying cloud of seismicity out to great distances. In contrast, injecting water into basement rock generated a compact swarm of earthquakes within a kilometer of the disposal site. The larger earthquakes produced in these cases were smaller than those produced in sedimentary rock.
This was a huge surprise. The conventional wisdom is that injecting fluids into basement rock is more dangerous than injecting into sedimentary rock because the largest faults, which potentially can make the most damaging earthquakes, are in the basement. Mitigation strategies around the world are premised on this idea, but our data showed the opposite.
How wastewater injection can make earthquakes: In basement rocks (left), injection activates faults in the small region directly connected to the added water, shown in blue. In sedimentary injection (right), an additional halo of squeezed rock, shown in red, surrounds the pressurized fluid and can activate more distant faults. Thomas Goebel, CC BY-ND
Why would injecting fluids into sedimentary rock cause larger quakes? We believe a key factor is that at sedimentary injection sites, rocks are softer and easier to pressurize through water injection. Because this effect can extend a great distance from the wells, the chances of hitting a large fault are greater. Poroelasticity appears to be generating earthquakes in the basement even when water is injected into overlying sedimentary rocks.
In fact, most of the earthquakes that we studied occurred in the basement, even at sedimentary injection sites. Both sedimentary and basement injection activate the deep, more dangerous faults – and sedimentary sequences activate more of them.
Although it is theoretically possible that water could be transported to the basement through fractures, this would have to happen very fast to explain the rapid observed rise in earthquake rates at the observed distances from injection wells. Poroelasticity appears to be a more likely process.
Avoiding Human-Induced Quakes
Our findings suggest that injection into sedimentary rocks is more dangerous than injecting water into basement rock, but this conclusion needs to be taken with a rather large grain of salt. If a well is placed at random on Earth's surface, the fact that sedimentary injection can affect large areas will increase the likelihood of a big earthquake.
However, wells are seldom placed at random. In order to efficiently dispose of wastewater, wells must be in permeable rock where the water can flow away from the well. Basement rocks are generally low permeability and therefore are not very efficient areas in which to dispose of wastewater.
One of the few ways that basement rocks can have high permeability is when there are faults that fracture the rock. But, of course, if these high permeability faults are used for injection, the chances of having an earthquake skyrocket. Ideally, injection into basement rock should be planned to avoid known larger faults.
If a well does inject directly into a basement fault, an anomalously large earthquake can occur. The magnitude 5.4 Pohang earthquake in South Korea in 2017 occurred near a geothermal energy site where hydraulic injection had recently been carried out.
The important insight of this study is that injection into sedimentary rocks activates more of these basement rocks than even direct injection. Sedimentary rock injection is not a safer alternative to basement injection.
Reposted with permission from our media associate The Conversation.
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Jean-Marc Neveu and Olivier Civil never expected to find themselves battling against disposable mask pollution.
When they founded their recycling start-up Plaxtil in 2017, it was textile waste they set their sights on. The project developed a process that turned fabrics into a new recyclable material they describe as "ecological plastic."
Mounting Piles of Waste<p>It is not only the streets of Chatellerault where pandemic pollution is piling-up, but also the world's beaches and oceans. Once there, they can take up to 450 years to degrade and disappear.</p><p>Esther Röling, co-organizer of the annual Adventure Clean Up Challenge held on Hong Kong Island, has seen this waste firsthand. In October the sports challenge pitted teams against one another in a competition to remove trash from 13 hard-to-reach coastal areas around the city.</p><p>They find tons of both disposable and reusable masks, said Röling. "You wonder how it ended up there. Was it just thrown on the ground? Or was it in a garbage bag that broke open?"</p><p>Almost 10,000 kilometers away in Antibes on the sunny French Riviera, it's a similar picture. For the past few months, divers and clean-up volunteers working with an ocean clean-up non-profit called Operation Mer Propre have been collecting an increasing number of masks found on land and in the sea.</p><p>"Since the beginning of the lockdown when we started to count, we've reached 800, 900, [and now in total] 1000 masks," said co-founder Joko Peltier. </p><p>According to <a href="https://unctad.org/news/growing-plastic-pollution-wake-covid-19-how-trade-policy-can-help" target="_blank">UN estimates</a>, up to 75% of all coronavirus-related plastic could end up as waste in oceans and landfills.</p>
The Limits of Recycling<p>Yet not all are convinced the recycling of this waste is possible on a global scale. </p><p>"What those citizen groups are doing is really beneficial but once they collect it, it should just go to a landfill or an incinerator. They shouldn't necessarily expect it to get recycled," said Jonathan Krones, an industrial ecologist and visiting assistant professor of environmental studies at Boston College.</p><p>That's because mask recycling programs like Plaxtil are few and far between and most don't have the benefit of a readily adaptable production process. </p><p>Even in countries with solid recycling infrastructure, he says, the system is designed to separate out specific types of waste like bottles or cardboard.</p><p>"I imagine that it would be technically feasible to develop a separation process to filter out masks, but there simply aren't enough of them to make that economical," he said.</p><p>Collection is a big hurdle, he adds. Since each mask only weighs a fraction of a gram and they're scattered on roads or mixed with other trash, it is difficult and costly. </p><p>"You need a lot of raw material of the right quality to make investing in the recycling technology and the recycling system worthwhile," he said.<span></span><br></p>
Hemp, Sugar Cane and Sustainable Alternatives<p>Some projects are instead addressing the material used to make masks.</p><p>French company Geochanvre have created a mask made primarily from hemp, while in Australia, researchers at the Queensland University of Technology are experimenting with a disposable product made from agricultural waste. </p><p>Biodegradable options are exciting alternatives to reduce the fossil fuels needed for the creation of plastic-based masks, said Krones, but they don't absolve the wearer from the responsibility of what happens afterwards. </p><p>Bio-based masks often need their own composing solutions, he explains, because in landfill they can produce high amounts of the greenhouse gas methane when anaerobic bacteria feeds on the organic material. Methane is known to be significantly more potent than carbon dioxide.</p><p>"I think as long as we have in our mind that we want to have disposability, we're going to have to wrestle with a variety of different sorts of environmental tradeoffs," he said, adding that reusable, fabric masks are the best option available to most people.</p><p>Precimask is developing a clear face covering with an optional visor made from hard plastic, designed to be long-lasting.<br></p><p>Air enters either side of the cheeks through a technology normally found in pool filters and car exhaust systems, said company spokeswoman Juliette Chambet.</p><p>"We wanted to make ceramic-based filters that would be washable and cleanable, which would allow them to be reused as many times as desired without having to buy a new consumable or produce waste," she said. </p><p>Ultimately, encouraging mask wearers to think about the entire lifecycle of a mask is key, explains Neveu. </p><p>"We want people who put on the masks to realize that they are also responsible for the waste, he said. "It's not inevitable that this [pandemic] will become an environmental catastrophe.</p><p><em>Reposted with permission from </em><em><a href="https://www.dw.com/en/covid-19-recycling-pollution-trash-pandemic/a-55707817" target="_blank">Deutsche Welle</a>.</em><a href="https://www.ecowatch.com/r/entryeditor/2649032193#/" target="_self"></a></p>
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