Features of fractal dimension anomaly of radon content in underground water in North China before and after the 1976 Tangshan earthquake

Based on the fractal theory, proceeding from the observed data of the radon content of underground water, thefractal dimension of the sequence of sudden changes of the radon content of 27 wells (springs) in North Chinabefore and after the Tangshan earthquake has been calculated using a month-by-month sliding method. Thevariation of fractal dimensions anomalies before and after the main shock in time and space was studied. The following phenomena were discovered: The fractal dimension of the radon content changed distinctly before theearthquake;the stations where the fractal dimension anomalies of the radon content appeared are within 300 kmfrom the epicenter;the increase and decrease areas of the fractal dimensions of the radon cogtent appeared clearly; just before the earthquake, the increase area filled the whole of North China except the epicentral area,where the fractal dimensions are decreasing.