[en] Radon anomalies prior to an earthquake have been considered as an important precursor for earthquake prediction. The study of radon anomalies for earthquake prediction, however, require long term continuous monitoring. The solid state nuclear track detectors are well suite for such study. The radon concentration variations, prior to an earthquake, have been observed at four different stations by us with variable detector exposure time and holes, having different depths augured for radon monitoring. A positive correlation has been observed between radon build up and occurrence of an earthquake at many instances even when the distances between the radon monitoring stations and earthquake epicenters was as far as hundreds of kilometers. It has further been observed that radon signal for the arrival of an earthquake is received earlier and more enhanced in deeper holes in which radon monitoring device (steel tube containing CN-85 plastic track detector) is placed. (author)