水力压裂法会诱发地震吗？

    近十年来，拜得克萨斯州沃思堡西北部的巴涅特页岩层(Barnett Shale)掀起的“水力压裂法”热潮所赐，美国更加接近能源独立的目标。但意想不到的是，一场因天然气钻探引发的暴动正在此地的一小片区域蓄势待发。

    向来支持能源业的得克萨斯州眼下正在应对地震难题。

    自11月1日以来，阿斯莱周围的农村地区（约1.1万人口）遭受了30多场小型地震的袭击。许多居民抱怨称，地震频发的罪魁祸首是地下处置井——钻探公司用它们来处理压裂和生产过程产生的废水。钻孔机向这些一两英里深的处置井注入含盐废水。

    这些地震已经引发了一场喧嚣的市政厅会议，监管当局已经决定聘请得克萨斯州有史以来首位州级地震学家，同时还承诺研究这个问题。但是，因为对这个答复不满，一批居民上周二乘坐巴士来到奥斯汀，涌入得克萨斯铁路委员会(Texas Railroad Commission，向来支持能源业的得克萨斯州石油和天然气监管机构)的会议现场，强烈要求立即关闭处置井。据《沃斯堡明星电讯报》(Fort Worth Star-Telegram)一位记者报道，一位抗议者当场拿出一把吉他，唱起了猫王的代表作《地动山摇》(All Shook Up)。

    最大的问题是：处置井到底是不是正在引发地震？

    阿斯莱的兼职市长，保险代理人艾伦•布伦德里特对此确定不疑。布伦德里特回忆起了11月份一次市议会会议期间他首次经历地震的情景。“那种感觉就像是有人踢了一下你的椅子后背，非常奇怪。”12月份一天刚过半夜的时候，他又感受到了另一次地震。他当时正躺在自己三居室家中一个躺椅上看一部惊悚片。“听起来就像是有什么东西在外面爆炸了一样，”布伦德里特说。“整个房子都在晃动，窗户哐哐作响。我嗖地一下从椅子上跳了起来，大约跳了两英尺远。”

    此地向北几英里的里诺市（这座小城附近几个活跃的处置井被怀疑是地震中心），市议会厅的墙壁和地板上出现了不少裂痕。当地一些居民指责称，地震导致他们的房产下沉，卡住了家中的门窗。布伦德里特说，“我认识的所有人都给他们的手机下载了一款地震应用程序。”（QuakeFeed是最受欢迎的一款应用）

    据美国地质调查局(U.S. Geological Survey)地球物理学家威廉•埃尔斯沃思博士介绍，这些地震的级别介于里氏2.0级至3.6级之间，其中9次为3.0级以上。虽然成千上万居民都感受到了冲击，而且因此惊恐万分，但迄今为止，这些地震还没有造成人身伤害，也没有导致重大损失。

    以打破页岩提取石油和天然气为特征的水力压裂技术一直被视为各种弊病（包括水井污染）的源头。但地质学家认为，构成更大地震风险的不是水力压裂法，而是为地下注入数百万加仑污水的处置井。

    埃尔斯沃思博士正在帮助协调确定地震模式的各种努力，其中包括在这个地区安装地震仪。他说，注水井造成地震的情形非常罕见，但有强有力的证据表明，少数注水井（或许靠近现有的地质断层）的确会引发地震。在得克萨斯州，“一切都发生在非常有限的区域内。我们不知道在这个时点是否存在某种联系。两者确实存在相关性，但相关性不是因果关系，人们需要记住这一点。”

    In a small patch northwest of Fort Worth, Texas -- where the Barnett Shale set off the decade-long "fracking" boom that's moved the U.S. closer to energy independence -- there's a surprising uprising brewing over drilling for natural gas.

    Energy-friendly Texas is now dealing with earthquakes.

    Since Nov. 1, more than 30 small temblors have struck the rural area around Azle (pop. 11,000), and many residents are blaming the quakes on underground disposal wells, used to get rid of wastewater generated during the fracking and production process. Drillers inject the salty wastewater into wells a mile or two deep.

    The quakes have already triggered a raucous town hall meeting, a decision to hire Texas's first-ever state seismologist, and a pledge to study the problem. Unsatisfied with this response, a busload of residents, demanding that the disposal wells be shut down immediately, appeared on Tuesday in Austin at a meeting of the Texas Railroad Commission, the state's industry-friendly oil-and-gas regulator. According to an account by a Fort Worth Star-Telegram reporter, one protester pulled out a guitar during the meeting and broke into a rendition of Elvis Presley's "All Shook Up."

    The big question: Are the disposal wells causing the earthquakes?

    Alan Brundrett, an insurance agent who serves as Azle's part-time mayor, has no doubt. Brundrett recalls the first earthquake he experienced, during a city council meeting in November. "It felt like someone kicked the back of your chair. It was strange." He felt another shortly after midnight in December, as he was lying in a recliner in his three-bedroom home, watching a horror flick. "It sounded like something exploded outside," says Brundrett. "The whole house shook, and the windows rattled. I jumped about two feet out of my chair."

    In tiny Reno, a few miles to the north -- near the site of active disposal wells and the suspected epicenter of the shaking -- cracks have appeared in the walls and floor of the city council chamber. Some area residents blame the quakes for sinkholes on their property and stuck doors and windows in their homes. Now Brundrett says, "everybody I know has an earthquake app loaded on his cellphone." (QuakeFeed is a favorite.)

    The tremors have ranged from 2.0 to 3.6 on the Richter scale, with nine measuring 3.0 or higher, according to U.S. Geological Survey geophysicist Dr. William Ellsworth. While frightening and felt by thousands of residents, none of the quakes so far has caused injuries or major damage.

    Hydraulic fracturing (which breaks apart shale rock to extract oil and gas) has been blamed for various ills, including contamination of water wells. Yet geologists say it's not the fracking, but rather disposal wells -- which inject millions of gallons of water deep underground -- that pose the greater risk of meaningful earthquakes.

    Ellsworth, who is helping coordinate efforts to zero in on the pattern (including the installation of seismographs in the region), says few injection wells cause earthquakes, but there is strong evidence that a handful of them -- perhaps located near an existing fault -- do. In Texas, says Ellsworth, "everything is happening in a very limited area. We don't know that there's a connection at this point. There's a correlation, but correlation is not causation. People need to keep that in mind."