NATURE OF SOIL GAS RADON RELEASE AND EARTHQUAKE PREDICTION
The spectra of continuous monitoring of soil gas radon with an improved solid-state detector placed in an active fault zone in south central Taiwan appear to support these theoretical predictions. The observation is a quick raise in radon level about a couple of weeks before a noticeable earthquake, and a peak precursor one to seven days before the occurrence. Noticeable earthquakes occur frequently in Taiwan that permits us to recognize stressed and relaxed states of the rock formations by using the recorded radon spectrum. With additional radon detecting units, a stress domain could also be determined. In addition, radon is found to correlate with total soil gas in release rate from measurements of gas bubbles out of a pond in a fault zone. Radon correlates with CH4 and C2H6 in release rate as well. However, radon has larger fluctuations over time than CH4and C2H6,and thus a better precursor. Other gases measured, including CO2, H2, He, H2O, N2, O2 and Ar, are not sensitive to earthquakes. An identical radon monitoring system is placed over North American craton in Akron for comparison. Soil gas radon level is low and variation over time is small when compared with the recordings in Taiwan.