South Korea's Most Damaging Earthquake Linked to Geothermal Fracking
The 5.5-magnitude temblor that struck the city of Pohang on Nov. 15, 2017 was the second most powerful on record and its most damaging, leaving the infrastructure in ruins, injuring dozens of people and leaving about 1,500 homeless.
Hydraulic fracturing, aka fracking, works by injecting high-pressure fluid underground to fracture rock in order to achieve increased rates of flow. Fracking is often associated with unlocking oil and natural gas deposits, but in this case, the intention was to enable circulation to produce geothermal energy.
Using geological and geophysical data, South Korean researchers from one of the studies suggested that the Pohang earthquake was induced by fluid from an enhanced geothermal system site that was injected directly into a near-critically-stressed subsurface fault zone.
Kwanghee Kim, a seismologist at Pusan National University and lead author of the study, explained that the well's high-pressure water lubricated an unknown fault in the rock, causing it to slip and trigger the quake.
In the second study, researchers from the University of Glasgow, ETH-Zurich in Switzerland, and GFZ-Potsdam in Germany found that the mainshock and its largest aftershocks occurred within 2 kilometers or less of the geothermal site, where many thousands of cubic meters of water were injected under pressure into boreholes.
#FRACKING LINKED TO SOUTH KOREAN EARTHQUAKE A 2017 earthquake in South Korea which injured close to 100 people was… https://t.co/BnrPc3kiwS— University of Glasgow (@University of Glasgow)1524827306.0
They also determined that the mainshock and the 46 aftershocks detected between Nov. 15-30 all occurred at depths of 3 to 7 kilometers, which is unusually shallow compared to previous quakes in the area.
"It would be a very remarkable coincidence if this earthquake were to be unrelated to the activity at the site, given that it occurred so close to it," Robert Westaway, a senior research fellow at Glasgow university's school of engineering, and one of the paper's co-authors, told The Guardian. "My own personal view is that it is highly likely there is a connection."
Other research has linked fracking for oil and gas to anthropogenic, or man-made, earthquakes, including a 4.8-magnitude earthquake in 2016 in northern Alberta. The alarming swarm of quakes currently rocking Oklahoma has been connected to the disposal of large volumes of wastewater from oil and gas production into underground wells.
Geothermal energy is often touted as a source of clean power, but previous studies have also found that drilling deep into Earth to tap its natural heat could cause seismic activity, thus raising questions about the long-term risks of this energy source.
"If the Pohang earthquake proves to be human-caused, it would be the largest known associated with deep geothermal energy, and this would certainly impact future projects," team member Stefan Wiemer of the Swiss Seismological Service told New Scientist.
Two 4.2-Magnitude Earthquakes Rattle Northern Oklahoma in a Single Evening https://t.co/zLuJDM8q9u @foodandwater… https://t.co/MYl1FDPlFv— EcoWatch (@EcoWatch)1520304904.0
The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.
"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."
The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.
They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.
They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.
But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.
"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.
What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.
It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.
To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.
First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.
Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.
University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.
"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."
Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.
"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.
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