IMMINENT ANOMALIES OF RADON CONTENT BEFORE LARGE EARTHQUAKES IN CHINA

Just before the large earthquakes in Bohai, Haicheng, Luhuo, Tangshan, and Songpan in northern and southwestern China, anomalous changes in radon content in groundwater from wells and springs were recorded at most of the observation stations. From the compilation of the records of radon anomalies, characteristic features of the imminent radon changes prior to a large earthquake are derived: (1) spike-like anomalous changes; (2) inhomogeneity of the spatial distribution of the anomalies around the epicentral area; and (3) migration and spatiotemporal evolution of anomalies. Understanding of the characteristics of radon anomaly is of importance and will contribute much to the prediction of an impending large earthquake.