Anomalous radon emission as precursor of earthquake

Recent years have seen an ever increasing interest in studying the usefulness of radon measurements in earth sciences. Radon emissions that are enhanced by forthcoming geophysical events as earthquakes or volcanic activity have been observed all over the world. The abnormal radon exhalation from the interior of earth, as a precursory phenomenon related to earthquakes and as an indicator of underlying geological faults, is an important field of investigation. For this purpose a number of active and passive methods for getting radon signals have been developed. Several models have been proposed as an explanation of the experimental field data. This paper gives a brief review of the progress made in the field of radon measurements in earth sciences specially in predicting earthquakes. Radon anomalies that have been observed in soil gas as well as groundwater or spring prior to earthquakes have been reviewed in this paper. The models proposed in relating precursor time, epicentral distance, magnitude of earthquake have also been discussed.