One of the more intriguing precursors to earthquakes is the eanation of radon gas from the ground. Radon, a colorless, odorless, radioactive gas, is trapped within all rocks, and when rocks are fractured, as they are prior to earthquake, the gas is released in greates quantities than usaual. (Radon is always eenating from the ground in small quantities.) It is theorized that these excessive quantities of radon can work their way toward the surface, where they can be detected by sensitive strips of film buried a few feet underground. Radon has been used to successfully predict a few earthquakes in China , the Soviet Union, and the United States. In some cases, it has been the only precursor used to predict the activity successfully. In others, it has been simply one of many precursors observed and subsequently used to predict the seismic events.
When if is successfully used to predict earthquakes, the increase in the level of radon emantion generally occurs four to six week prior to the earthquake it precedes. As with all other precursors discovered and tested, however, radon emanation is not foolproof. Some earthquakes are preceded by increases in the radon level can often be caused by other phenomena, such as changes in water level (caused by something other than seismic activity) and changes in barometric pressure, thus leading to false alarms. Using radon to predict earthquakes, therefore, has recently fallen into disfavor.
Scientists now believe that large quantities of radon coe to the surface as a result of soething other than seismic activity. There are other gases that are hydrogen, helium, carbon dioxide, and methane. For two month prior to the 1975 China earthquake, farm workers reported an extreely strong odor in the fields.
On some days, it was so strong that it actually forced them to stop working. One worker observed gas bubbles bursting from a trench, and another lost consciousness. This information, too, was used by the Chinese to Predict the February cataclysm. In Japan, research shows a clear correlation beteen hydrogen released from the eart and seiskic activity (fault movement). Studies on the release of helium from the ground in California are proving helpful, as scientists are coming up with relatively good precentages of prediction.
