阿肯色州的城市在地震中感受到原因不明的浪湧

阿肯色州的城市在地震中感受到原因不明的浪湧
Ark. Cities Feel Unexplained Surge In Earthquakes
by The Associated Press
A LITTLE ROCK, Ark.
February 17, 2011, 09:45 am ET
Translation by Autumnson Blog

Jim Sutterfield was briefly puzzled by a thumping sound that seemed to slam the back of his office chair. But when the small-town Arkansas fire chief turned and saw no one was around, he quickly realized it was just an earthquake — again.
吉姆塞打菲爾特簡短地被一重擊聲困惑，似乎猛推他的辦公室椅背。但當小城鎮的阿肯色州消防隊長轉身和看不到有人在旁邊，他很快意識到這只是一場地震 - 再一次。
"That was only my second time to feel one, but others here have felt them for three or four months now," Greenbrier chief Jim Sutterfield said after feeling the latest tremor on Wednesday. "Now when it happens, people say, 'Well, there's another one.'"
“那只是我的第二次去感受一下，但這裡的其他人現在己感受它們三或四個月了，”綠薔薇隊長吉姆塞打菲爾特週三在感受到最新的地震後說。 “現在當它發生時，人們會說，'好吧，有另外一次了。”
Several small earthquakes ranging in magnitude from 1.8 to 3.8 have rattled the north-central Arkansas cities of Greenbrier and Guy this week, and the cause is unknown.
幾次小地震震級從 1.8到3.8不等，這一周已困擾阿肯色州中北部城市綠薔薇和佳，和原因是不明的。
The U.S. Geological Survey has reported more than 30 earthquakes in the area since Sunday, including a magnitude 3.8 quake Thursday morning and at least 16 others occurring Wednesday, two of which were magnitude 3.2 and 3.5. More than 700 quakes have occurred in the region over the past six months.
美國地質調查局自上週日以來已在該地區報告超過30次地震，包括週四上午的一次裡氏3.8級地震，和至少在星期三發生另外的16次，其中兩次是3.2和3.5級。在過去六個月該地區已發生超過 700次地震。
Scott Ausbrooks, geohazards supervisor for the Arkansas Geological Survey, said the quakes are part of what is now called the Guy earthquake swarm — a series of mild earthquakes that have been occurring periodically since 2009. A similar swarm occurred in the early 1980s when a series of quakes hit Enola, Ark.

Ausbrooks said geologists are still trying to discover the exact cause of the recent seismic activity but have identified two possibilities.

"It could just be a naturally occurring swarm like the Enola swarm, or it could be related to ongoing natural gas exploration in the area," he said.

A major source of natural gas in Arkansas is the Fayetteville Shale, an organically-rich rock formation in north-central Arkansas. Drillers free up the gas by using hydraulic fracturing or "fracking" — injecting pressurized water to create fractures deep in the ground.

Ausbrooks said geologists don't believe the production wells are the problem, but rather the injection wells that are used to dispose of "frack" water when it can no longer be re-used. The wastewater is pressurized and injected into the ground.

"We see no correlation between natural gas production wells and earthquakes, but we haven't ruled out injection wells," he said, adding that if production wells were the cause, the earthquakes would be scattered all over the region underlain by the Fayetteville Shale formation and not in just one area.

Ausbrooks said the earthquakes are occurring in the vicinity of several injection wells.

Guy Police Chief Dave Martini said the locals continue to blame the gas companies for the quakes.

"We have a disposal well here just outside of the city," Martini said. "People are suspecting that to be causing it, even though there isn't any proof of that."

Martini said the earthquakes started increasing in frequency over the past week and that the disposal well has seen an increase in use recently.

Lawrence Bengal, director of the Arkansas Oil and Gas Commission, said a six-month moratorium was established in January on new injection wells in the area. He said four companies are operating already-drilled injection wells: SEECO Inc., Chesapeake Operating Inc., Clarita Operating LLC and Deep-Six Water Disposal Services LLC.

The moratorium, which is expected to end in July, is intended to allow time to study the relationship — if any — between the injection wells and earthquakes in the area.

The largest quake of the Guy Earthquake Swarm was a magnitude 4.0, which occurred in October, Ausbrooks said. The region could possibly see quakes reaching as high as 5.0, but he said anything above 6.0 is unlikely.

The magnitude scale for earthquakes is logarithmic, meaning a magnitude 3 earthquake would produce waves with amplitudes 10 times greater than a magnitude 2 and 100 times greater than a magnitude 1. Geologists say quakes of magnitude 2.5 to 3.0 are generally the smallest felt by humans.

"These periods of high activity are not uncommon. I don't think it's anything to be overly concerned about," Ausbrooks said. "We always encourage people to keep tuned in to what's going on and to always have an all-hazards disaster preparedness kit."

http://www.npr.org/templates/story/story.php?storyId=133828657

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