U.S. Maps Pinpoint Earthquakes Linked to Quest for Oil and Gas
By RICHARD PÉREZ-PEÑA

The United States Geological Survey on Thursday released its first comprehensive assessment of the link between thousands of earthquakes and oil and gas operations, identifying and mapping 17 regions where quakes have occurred.

The report was the agency’s broadest statement yet on a danger that has grown along with the nation’s energy production.

By far the hardest-hit state, the report said, is Oklahoma, where earthquakes are hundreds of times more common than they were until a few years ago because of the disposal of wastewater left over from extracting fuels and from drilling wells by injecting water into the earth. But the report also mapped parts of eight other states, from Lake Erie to the Rocky Mountains, where that practice has caused quakes, and said most of them were at risk for more significant shaking in the future.

“Oklahoma used to experience one or two earthquakes per year of magnitude 3 or greater, and now they’re experiencing one or two a day,” Mark Petersen, the chief author of the report, said. “Oklahoma now has more earthquakes of that magnitude than California.”

The report came two days after Oklahoma’s state government acknowledged for the first time the scientific consensus that wastewater disposal linked to oil and gas drilling was to blame for the huge surge in earthquakes there. The state introduced an interactive map showing quake locations and places where wastewater is injected into the ground, and the state-run Oklahoma Geological Survey said it “considers it very likely” that the practice is causing most of the shaking.

Hydraulic fracturing, a drilling technique that injects a high-pressure mix of water and chemicals into the ground to break rock formations and release gas, has drawn widespread attention. But injecting water to dispose of waste from drilling or production is a far greater contributor to earthquakes. The federal report excluded human activity, like mining, that can cause quakes but does not involve large-scale fluid injection.

In one of the 17 areas identified in the report, around Colorado’s Rocky Mountain Arsenal, injections of chemical waste set off earthquakes starting in the 1960s. But the vast majority of the quakes since then have involved oil and gas production.

Many scientific reports, published over decades, have said that pumping fluids into the ground at high pressure can set off earthquakes. But until fairly recently, energy companies and regulators in some energy-producing states insisted that the link was still in doubt.

Most affected states have now acknowledged it, but Oklahoma had not until the recent statements by officials there. Still, state regulators around the country have not gone as far in controlling industry practices as environmental groups have asked, and there is little sign that the new federal findings will goad them to go farther.

Matt Skinner, a spokesman for the Oklahoma Corporation Commission, the state’s top regulatory body for oil and gas exploration, said Oklahoma already required a “seismicity review” for proposed wells. “Any tool we can use in response to triggered seismicity,” he said of the new report, “would be important to us.”

Asked about the report, Lawrence E. Bengal, director of the Arkansas Oil and Gas Commission, also pointed to what his state had already done, after a surge in earthquakes north of Little Rock in 2010 that made the state second only to Oklahoma in induced quakes.

The commission imposed a moratorium “prohibiting the drilling of any new disposal wells in the area where the earthquake activity had occurred,” Mr. Bengal said, ordered the four active wells in the area plugged and ruled that seismic activity must be taken into account when allowing new disposal wells in other parts of the state.

Last year, the Railroad Commission of Texas and the oil and gas industry there agreed to new rules allowing the commission to shut down old wells and deny permission for new ones based on earthquake risks.

The issue has serious political, economic and environmental implications, particularly in the nation’s midsection, where energy production and related jobs have soared. The American Petroleum Institute did not respond to a request for comment on the report.

The report said two adjacent regions were most affected: one largely in northern Oklahoma but extending into southern Kansas, and the other stretching from central Oklahoma to the Texas border, where seismic activity has soared in the last six years.

It also mapped parts of Texas where it said wastewater injection wells had produced quakes, including the heavily populated Dallas-Fort Worth area. Other risk areas named were in Colorado, including one that extends into Utah, and in Alabama, Arkansas, New Mexico and Ohio.

“We’re seeing these induced earthquakes much more often than we ever used to, in multiple parts of the country, and we need to try to understand the risks and how to deal with them,” Mr. Petersen said.

Thousands of small quakes occur every year around the country, noticed only by the jittering needles of seismographs; a magnitude 3 temblor is felt by some people relatively close by, but the only harm is to their nerves. But the scale used to measure earthquakes is logarithmic, meaning that a magnitude 4 quake is 10 times as powerful as a magnitude 3, and a magnitude 5 — strong enough to do some structural damage — is 10 times as powerful as a magnitude 4.

In 2011, central Oklahoma experienced the most powerful earthquake recorded in the state, a 5.6-magnitude shock that scientists have also called the nation’s biggest human-induced quake. By comparison, the major quake that struck Los Angeles in 1994 measured 6.7, and the one that hit the San Francisco Bay Area in 1989 measured 6.9.

The highly technical report was a step toward predicting the risk from human-caused quakes, which it conceded was extremely hard to do. “Difficulties in assessing seismic hazard arise from a lack of relevant technical information on human industrial activity (that is, pumping data for injection wells),” the report said.

Mr. Petersen noted that wastewater disposal and related earthquakes “fluctuate year by year based on economic and policy decisions, which are very difficult to predict.” In fact, the report shows that in places where wastewater injection stopped, earthquake frequency fell to near zero — notably, in central Arkansas since 2011 and in an area north of Denver in the 1970s.

Predicting risk is also hard, the report noted, because there is no scientific consensus on just how powerful such quakes can be. The report estimated the effects of shocks up to magnitudes 6 and 7, while noting that some scientists have speculated that the catastrophic 7.9-magnitude earthquake in China in 2008 was caused by human activity.

“I’m not necessarily saying that we’re going to have a 7 in Oklahoma,” Mr. Petersen said. “But I don’t think we can rule that out.”

Scientists have also posited that human-caused quakes could lead to additional ones on naturally occurring faults nearby.

The agency’s assessments of naturally occurring earthquake risks are often used to help determine building codes and set insurance rates. Buildings in the middle of the country, unlike those on the West Coast, generally do not have to meet seismic safety standards.

科學家：開採石油誘發地震大增

科學家愈來愈肯定，石油、天然氣開採在美國引起數百次地震；雖然這些地震的規模多數很小，而且未引起嚴重損壞，專家卻認為，它們可能導致更危險大型地震出現的機率大幅增加。

油氣開採業者辯稱，這種關聯需要更多研究結果佐證，然而迅速累積的證據可能使業者受到更嚴格的規範，同時使它們的勘採計畫更難以獲得批准。

哥倫比亞大學全球能源政策中心主任波多夫表示，人為引發地震是「重要且合理的懷疑，主管當局與業者必須嚴肅以對」。他又說，業者與各州可以採取的具體因應措施包括，更嚴密監控開採作業，採用更嚴格的標準，回收使用來自開採作業的廢水，而不是把它們注入地下。

根據許多相關報告，美國油氣開採業過去幾年欣欣向榮，雖然創造許多就業機會與稅收，卻與小型地震大增息息相關。

美國地質調查所（USGS）23日公布一項大範圍地圖，標出美國東部與中部17個經常出現地震的地區；研究人員說，這些地震是油氣開採作業引起；USGS在報告中指出，與開採作業有關的人為地震不斷增加中。

科學家認為，業者將廢水注入地層深處是人為地震次數增加的主因，因為這很可能觸動原本靜止的斷層。USGS地球物理學家艾爾斯華斯表示，將廢水注入地層深處「顯然」可能導致斷層移動。美國業者採用所謂的水裂開採法，也就是將大量的水、砂及化學藥品混合物注入岩層，使岩層裂開後，釋出石油或天然氣。

數十年來，美國中部與東部各州比較擔心龍捲風、洪水與颶風，地震是其次。然而2009年起，這些地區的地震次數大幅增加，一些令人料想不到的地區甚至也開始出現地震，包括阿拉巴馬、阿肯色、科羅拉多、堪薩斯、新墨西哥、俄亥俄、奧克拉荷馬與德州的部分地區。

原文參照：
http://www.nytimes.com/2015/04/24/us/us-maps-areas-of-increased-earthquakes-from-human-activity.html

2015-04-24．聯合晚報．A6．國際焦點．編譯陳世欽