More on the Link Between Earthquakes and Fracking Scientists from the United States Geological Survey have cautiously weighed in on a subject that has sparked public concern in some parts of the country: spates of small earthquakes in oil- and gas-producing areas. In a report to be presented next week at a meeting of seismologists in San Diego, the scientists say that increases in the number of quakes in Arkansas and Oklahoma in the last few years are "almost certainly" related to oil and gas production. But in a summary of the report, they say they do not know if seismic activity is increasing because companies are taking more oil and gas from underground or because of "changes in extraction methodologies." One "extraction methodology" that has become increasingly popular, especially for natural gas production, is hydraulic fracturing, or fracking, in which water and chemicals are injected into wells under pressure to create fissures in the rock and unlock the gas. A report by a state seismologist in Oklahoma suggested that two minor quakes in January, about 50 miles south of Oklahoma City, may have been directly caused by a fracking operation. But in central Arkansas, a series of hundreds of small quakes - and a few bigger ones - since 2010 was linked not to fracking itself but to disposal of waste liquids produced by the process. The waste was injected into deeper disposal wells. Scientists concluded that the liquids had migrated to a previously unknown fault, causing the quakes. A similar conclusion was reached by officials in Ohio this year after a series of quakes near a disposal well. In Oklahoma, in addition to the two quakes cited by the state seismologist's report, there have been many other small earthquakes in oil- and gas-producing areas. Some scientists have suggested these may be related to disposal wells rather than fracking itself, or perhaps simply to an increase in overall production.