From Lorraine Chow, EcoWarch.com, April 27, 2018

PHOTO: A Hyundai damaged from an earthquake in Pohang, South Korea on Nov. 15, 2017.

One of South Korea’s largest earthquakes was likely triggered by hydraulic fracturing associated with geothermal energy production, according to two studies published Thursday in the journal Science.

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.

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.

https://www.ecowatch.com/south-korea-earthquake-fracking-2563846110.html/

From CBS/AP (KOTV), Oklahoma City, OK

COVINGTON, Okla. — Earthquakes are rattling part of northwest Oklahoma where more than a dozen temblors have struck since Friday. The U.S. Geological Survey recorded an earthquake of magnitude 4.5 at 5:22 a.m. Monday, nearly an hour after a magnitude 3.3 quake struck the area near Covington, about 55 miles north of Oklahoma City.

Garfield County Emergency Management Director Mike Honigsberg says there are no reports of injury or severe damage from any of the quakes, which have ranged in magnitude from 2.4 to 4.6. The magnitude 4.6 earthquake that shook Oklahoma on Saturday was also felt in neighboring Kansas and Missouri, according to the USGS.

There have been 4 earthquakes with magnitudes ranging from 2.6 to 4.5 between Covington and Perry in northern Oklahoma in the past 24 hour. #okquake

Thousands of earthquakes have been recorded in Oklahoma in recent years, with many linked to the underground injection of wastewater from oil and natural gas production. State regulators have directed several oil and gas producers in the state to close injection wells or reduce volumes.

The strongest earthquake on record in Oklahoma was a magnitude 5.8 recorded near Pawnee on September 3, 2016, CBS affiliate KOTV reports.

https://earthquake.usgs.gov/earthquakes/map/ …

By Richard Nemec, NGI Shale Daily, April 9, 2018

Citing “strong” earthquake activity, the Oklahoma Corporation Commission (OCC) on Monday ordered reductions for a wastewater disposal well in the Covington/Douglas area of Garfield County as reports since last Friday have identified more than a dozen temblors in the northwestern part of the state.

The U.S. Geological Survey (USGS) recorded an earthquake with a preliminary magnitude 4.3 at 5:22 a.m. Monday, nearly an hour after a magnitude 3.3 quake struck the area near Covington.

The OCC’s Oil and Gas Conservation Division (OGCC) directed a disposal well in the area to reduce volumes being injected into the Arbuckle formation from 17,000 b/d to 5,000 b/d, noting the situation was ongoing and further actions may follow.

An OCC spokesperson told NGI’s Shale Daily that there are other wells in the area injecting into the Arbuckle.

“All of our actions in relation to these events have been reductions and/or shut-ins,” the spokesperson said. “All of those options are on the table in this case, and there are other Arbuckle disposal wells in the area.”

Over the past three years, state officials have shut in scores of wells and ordered reductions in response to swarms of low intensity seismic activity linked to the disposal wells.

The seismic activity has been linked to stepped up drilling activity in Oklahoma’s myriad reservoirs, including the STACK and the SCOOP, aka the Sooner Trend of the Anadarko Basin, mostly in Canadian and Kingfisher counties, and the South Central Oklahoma Oil Province.

Last week, there was a reported easing of small induced quakes in Oklahoma linked to oil and gas activity, while the risks from seismic events remained high, according to a study by the USGS.

http://www.naturalgasintel.com/articles/113965-oklahoma-orders-wastewater-disposal-curbs-in-response-to-multiple-quakes