ON THE ABNORMAL CHARACTERISTICS OF RADON CONTENTS IN THE SPRING WATERS NORTH OF THE EPICENTRAL AREA OF THE SUNGPAN-PINWU EARTHQUAKE BEFORE ITS OCCURRENCE AND THEIR CAUSE

In this paper the abnormal characteristics of radon contents in ground waters before the occurrence of the 1976 earthquake (M=7.2) in Sungpan—Pingwu area havebeen analysed. It is pointed out that in the epicentral region—Sungpan—and tothe north of it, within a distance of about 360 km radon contents in spring waters indicate a tendency of long-term continuous increase superimposed on which are short term variations, lasting about five years. A preliminary explanation of the phenomena is attempted. It is considered that the slow accumulation of tectonic strain in the epicentral area and its surroundings causes the increase of radon contents in spring waters within a broad area and for a long time. Radon in groundwater may be greatly increased when microfractures in the rock-bodies occur. Besides, the supply of spring water may be greatly accelerated by the enhanced vertical differential movement between crustal blocks causing short term variations of the radon contents.