Variations of helium and radon concentrations in soil gases from an active fault zone in southern Taiwan

Systematical analysis of soil-gas compositions was performed in the National Pingtung University of Science and Technology (NPUST) campus in southern Taiwan. The results show that the anomalous sites for helium, radon, nitrogen and carbon dioxide concentrations coincide with the surface trace of geological and geomorphological characteristics of the active Chaochou Fault. Some of these sites were chosen for soil helium and radon gas continuous monitoring at the suspected fault scarp. During a consecutive measurement for several months, a striking feature is that anomalously high concentrations appeared to be spike-like a few hours to a few days before the earthquakes. This result suggests that the variations in soil-gas compositions along the Chaochou Fault may reflect the regional crustal stress/strain changes prior to earthquakes.