Another moderate increase in tremors near the Assumption Parish sinkhole has prevented work on the 15.1-acre swampland hole since Wednesday, parish officials said Friday.
Known as micro-seismic earthquakes, officials say the tremors have not signaled more edge collapses are imminent in the gradually growing sinkhole between the Bayou Corne and Grand Bayou communities.
John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said the numbers of tremors have “not always” increased from the current level to the stage that usually ushers in edge collapses and burps of gas, crude oil and debris in the sinkhole.
“It’s going to really depend on the amount of events,” Boudreaux said.
The last slough-in and burp happened in mid-April after micro-earthquakes reached a frequency greater than the latest episodes.
Texas Brine, state and parish officials have said the tremors and surface slough-ins occur normally as the sinkhole finds its final shape and size.
The latest uptick in tremors comes as the evacuation order for 350 residents near the sinkhole hit its nine-month anniversary Friday.
Officials with the Louisiana Office of Conservation said Friday that devices measuring seismic activity have picked up “an increasing trend” in tremors associated with breaking rock and rock movement during the past few days.
Conservation and parish emergency officials halted work on the surface of the sinkhole as a result of the tremors.
Work elsewhere has continued while the micro-earthquakes were ranging from 10 to 50 per day.
The subsurface tremors are being detected around the sinkhole and Texas Brine Co.’s failed Oxy Geismar No. 3 salt dome cavern.
Scientists think the Texas Brine cavern was carved too close to the outer face of the Napoleonville Dome.
As a result, the cavern had a sidewall failure at a depth of 5,600 feet, allowing millions of cubic yards of rock to flow from outside the dome into the subterranean cavern and trigger the surface sinkhole. The cavern continues to fill with material surrounding the salt dome.
Earlier this week, Gary Hecox, a CB&I hydrogeologist working on the sinkhole, said past micro-earthquakes happened at the top of the Texas Brine cavern at 3,400 feet deep and at about 1,000 feet in the caprock on top of the Napoleonville Dome.