Researchers the world over are seeking reliable ways to predict earthquakes, focusing on identifying seismic¹（地震的） precursors² that, if detected early enough, could serve as early warnings. New research, published this week in the journal Applied³ Physics Letters, suggests that ozone⁴ gas emitted from fracturing rocks could serve as an indicator⁵ of impending⁶ earthquakes. Ozone is a natural gas, a byproduct（副产品） of electrical discharges into the air from several sources, such as from lightning, or, according to the new research, from rocks breaking under pressure.

Scientists in the lab of Raúl A. Baragiola, a professor of engineering physics in the University of Virginia School of Engineering and Applied Science set up experiments to measure ozone produced by crushing or drilling into different igneous⁷ and metamorphic rocks（变质岩） , including granite⁸（花岗岩） , basalt（玄武岩） , gneiss（片麻岩） , rhyolite（流纹岩） and quartz⁹. Different rocks produced different amounts of ozone, with rhyolite producing the strongest ozone emission¹⁰.

Some time prior to an earthquake, pressures begin to build in underground faults. These pressures fracture rocks, and presumably, would produce detectable¹¹ ozone.

To distinguish whether the ozone was coming from the rocks or from reactions in the atmosphere, the researchers conducted experiments in pure oxygen, nitrogen, helium and carbon dioxide. They found that ozone was produced by fracturing rocks only in conditions containing oxygen atoms, such as air, carbon dioxide and pure oxygen molecules¹², indicating that it came from reactions in the gas. This suggests that rock fractures may be detectable by measuring ozone.

Baragiola began the study by wondering if animals, which seem -- at least anecdotally -- to be capable of anticipating earthquakes, may be sensitive to changing levels of ozone, and therefore able to react in advance to an earthquake. It occurred to him that if fracturing rocks create ozone, then ozone detectors¹³ might be used as warning devices in the same way that animal behavioral changes might be indicators¹⁴ of seismic activity.

He said the research has several implications.

"If future research shows a positive correlation¹⁵ between ground-level ozone near geological faults and earthquakes, an array of interconnected ozone detectors could monitor anomalous¹⁶ patterns when rock fracture induces the release of ozone from underground and surface cracks," he said.

"Such an array, located away from areas with high levels of ground ozone, could be useful for giving early warning to earthquakes."

He added that detection of an increase of ground ozone might also be useful in anticipating disasters in tunnel excavation¹⁷, landslides¹⁸ and underground mines.

Baragiola's co-authors are U.Va. research scientist Catherine Dukes and visiting student Dawn Hedges.