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Israeli researchers have developed a model that may eventually enable scientists to predict earthquakes based on radon emission measurements in earthquake-prone areas.

The researchers - Gideon Steinitz, Ze'ev (Benny) Begin and Naama Gazit-Yaari of the Geological Survey of Israel - found that when there is a surge in emissions of radon gas within a particular area, there is a statistically high probability of an earthquake occurring in that area within the next three days. Their findings appear in the latest issue of the journal Geology, released this morning.

Earthquakes are caused when tectonic plates within the earth's crust shift, with the magnitude of the quake determined by the amount of energy the shift releases. Radon is formed by the radioactive decomposition of uranium, which is present in small quantities throughout the earth's crust. The researchers monitored radon emissions - which, being radioactive, are relatively easy to measure - in the Dead Sea Rift region of Israel for eight years. The rift is part of the Great Rift Valley stretching from Africa to Syria, which is one of the earth's major fault lines, and therefore, a frequent earthquake site.

The monitoring revealed that tectonic movements that produced earthquakes very often produced significant radon emissions a few days before the quake, although it was not always the case: Some earthquakes were not preceded by radon emissions, while radon emissions were not always followed by quakes. Therefore, while radon emissions should be viewed as a "sensitive indicator," the researchers wrote, they cannot yet be considered a firm predictor.

Another problem is that even when radon emissions do correctly predict a quake, they provide no indication as to its strength. So far, the researchers have detected no correlation between the strength of the radon emission and the strength of the quake.

They have also not been unable to determine exactly how long after an emission a quake will occur. Steinitz used an analogy from the medical world to explain the situation: "We've discovered the link between smoking and cancer, but we still can't say exactly who will develop cancer and when."

Nevertheless, he believes that the model developed is the first step toward a reliable prediction mechanism. But he acknowledges that this claim might be met with skepticism initially. "The scientific community has been very suspicious in recent years of people who claim they have found a system for predicting earthquakes," he said.

The attempt to discover a way to predict quakes was a hot topic in geology throughout the 20th century, and researchers have pursued a variety of different theories for this endeavor. Some, for instance, tried to observe changes in animal behavior before an earthquake, while others tested the theory that small tremors foreshadowed major earthquakes. But none of these methods proved reliable, and only once in the 20th century was a quake ever correctly predicted. That was in 1975, when Chinese scientists predicted a major quake hours before it happened, enabling one million Chinese to be evacuated from their homes, thereby significantly reducing the casualty level. In 1997, the prestigious journal Science even published an article claiming that earthquakes are impossible to predict.

Radon emissions have also often been studied in the past. But what made the Israeli team's work unique, was that it focused on a very specific region and studied that region intensively and systematically, Steinitz said.

The researchers have set up 12 radon measuring stations in the Dead Sea Rift region, and plan to establish more in the near future. Another seven monitoring stations have been built overseas with funding from the European Union. These stations, located in the Canary Islands, are meant to determine whether the significance of radon emissions is a local or general phenomenon.