After new reg­u­la­tions, quakes calm down a bit

The Denver Post - - NEWS - By Seth Borenstein

wash­ing­ton» The rate of earth­quakes in Ok­la­homa has dropped dra­mat­i­cally since late May, when the state lim­ited waste­water in­jec­tions into en­ergy wells, an As­so­ci­ated Press sta­tis­ti­cal anal­y­sis shows. And a new sci­en­tific study says the state is on its way back to calmer times that pre­vailed be­fore a huge jump in man-made quakes.

For quake-prone parts of Ok­la­homa, the state or­dered what is es­sen­tially a 40 per­cent re­duc­tion in in­jec­tion of the salt­wa­ter that sci­en­tists gen­er­ally blame for the mas­sive in­crease in earth­quakes. This year, be­fore the new rules went into ef­fect May 28, Ok­la­homa av­er­aged 2.3 quakes a day. Since then the av­er­age dropped to 1.3 a day, based on AP’s anal­y­sis of U.S. Ge­o­log­i­cal Sur­vey data of earth­quakes of mag­ni­tude 3.0 or larger. But some of those fewer post-reg­u­la­tory quakes have been large and dam­ag­ing.

“Def­i­nitely the rate of quakes has gone down,” said USGS geophysicist Robert Wil­liams. “At the same time we had more mag­ni­tude 5s this year than ever be­fore his­tor­i­cally in Ok­la­homa. It’s good news on one hand. It’s head­ing in the right direc­tion, but trou­bling to see th­ese large dam­ag­ing quakes in Pawnee and Cush­ing.”

Dur­ing the past cou­ple years, sci­en­tists have linked a dra­matic in­crease in earth­quakes in Ok­la­homa, Kansas and Texas to The av­er­age num­ber of daily earth­quakes of mag­ni­tude 3.0 or greater in Ok­la­homa de­clined in 2016 after new rules went into ef­fect lim­it­ing waste­water in­jec­tions into oil and gas wells:

the prac­tice of in­ject­ing waste­water from hy­draulic frac­tur­ing, or frack­ing, back un­der­ground after drilling for oil and gas. Higher vol­umes of waste­water in­jected are con­nected to more quakes with the flu­ids adding more pres­sure to tiny faults. After Kansas reg­u­lated waste­water vol­ume in March 2015, a Jan­uary AP anal­y­sis showed that Kansas felt fewer quakes, while less-reg­u­lated Ok­la­homa got more. In re­sponse, Ok­la­homa an­nounced new reg­u­la­tions.

This Novem­ber, Ok­la­homa had an av­er­age of less than a quake per day, al­though a 5.0-mag­ni­tude quake shook the vul­ner­a­ble Cush­ing area, where mas­sive oil re­serves are stored.

“The trend is ob­vi­ous,” said Stan­ford Uni­ver­sity pro­fes­sor Wil­liam Ellsworth. He said the AP num­bers were sim­i­lar, but not iden­ti­cal to a trend he cal­cu­lated us­ing a dif­fer­ent data­base and dif­fer­ent size earth­quakes. He said the new reg­u­la­tions were partly re­spon­si­ble for the falloff in earth­quakes, but he noted there also has been less drilling be­cause of a crash in oil prices.

Wil­liams of USGS said it is im­por­tant to put even the re­duced one-a-day quakes in con­text. Be­fore 2009, Ok­la­homa av­er­aged one mag­ni­tude 3.0 earth­quake a year; now it is good news that the rate is down to one a day, he said. In 2015, Ok­la­homa av­er­aged 2.3 mag­ni­tude 3.0 or larger quakes a day. In 2014, it was 1.6 per day.

A study pub­lished Wed­nes­day in the jour­nal Sci­ence Ad­vances by a dif­fer­ent Stan­ford seis­mol­o­gist, Mark Zoback, saw the re­duc­tion in Ok­la­homa quakes and used in­tri­cate com­puter sim­u­la­tions to show that the rate of earth­quakes will con­tinue to go down and even­tu­ally will re­turn to near pre-2009 lev­els. Wil­liams and Ellsworth, who weren’t part of the study, said Zoback’s work made sense.

“We’re not out of the woods yet. There is still a pos­si­bil­ity for po­ten­tially dam­ag­ing earth­quakes,” Zoback said. “It’s go­ing to take a few years for the sit­u­a­tion to re­turn to nor­mal.”

Ok­la­homa of­fi­cials said they plan to con­tinue the reg­u­la­tions and are ex­pected to re­lease a new di­rec­tive in the next cou­ple of weeks for the 15,000square-mile area where strong quakes rat­tled Pawnee and Cush­ing.

“Ob­vi­ously the goal is to bring seis­mic­ity down to what, for Ok­la­homa, would be con­sid­ered a nor­mal level. That’s the goal,” said Matt Skinner, a spokesman for the Ok­la­homa Cor­po­ra­tion Com­mis­sion, the agency that over­sees oil and gas operations. “Things will take time, but we’re go­ing to move ahead with ac­tions that will hope­fully make that time sooner rather than later.”

Ok­la­homa has had three quakes mag­ni­tude 5.0 or larger since 2014, and two of them oc­curred after the May reg­u­la­tions took ef­fect: the Septem­ber 5.8 in Pawnee and the Novem­ber quake in Cush­ing.

Pent-up pres­sure may be partly to blame, Zoback said.

And Wil­liams noted some in­ject­ing con­tin­ues.

Mainly, though, “we don’t un­der­stand the plumb­ing down there,” Wil­liams said.

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