Radon content of groundwater as an earthquake precursor: evaluation of worldwide data and physical basis.

Abstract

The properties of a worldwide data set of 91 radon anomalies (the frequency of occurrence, the precursor time interval, and the distribution of peak amplitudes) are correlated with earthquake data such as the respective magnitude and epicentral distance. These anomalies were reported as precursors to earthquakes in the US, USSR, China, Japan, and Iceland. Although the data set is incomplete and limited by experimental deficiencies, several consistent patterns emerge. Radon anomalies from different tectonic regions show similar patterns. The radon anomalies occur at greater epicentral distances for earthquakes of the larger magnitude. Anomalies preceding large earthquakes (M= or >6) are frequently observed at a distance of 100 to 500km. These distances are larger than several times the rupture dimensions of the future earthquakes. The time from the onset of an anomaly to the time of the earthquake (the precursor time) increases with magnitude but decreases with distance between epicenter and radon station. In addition, radon anomalies are observed more frequently prior to large earthquakes than prior to small ones, indicating that the preparation zone increases in size as magnitude increases.-Author