TEMPORAL AND SPATIAL DISTRIBUTION OF ANOMALOUS GROUND WATER CHANGES BEFORE THE 1975 HAICHENG EARTHQUAKE

This paper deals with a study of an empirical relation between the times and locations of abnormal ground water changes observed before the Haicheng Earthquake of 1975, based on a large amount of data, about 200 observation points. It is found that the points of abnormal ground water changes migrated toward the epicen-tral area of the Haicheng Earthquake from the surroundings before January 31, 1975 with a definite velocity. After that until the outbreak of the earthquake they returned from the epicentral area very quickly.By means of regressional analysis of the times and locations of the anomalous ground water changes, it can be shown that prior to January 31, 1975 the relation between the times and locations is linear. It is also assumed that this relation reflects a possibility that before the Haicheng Earthquake the crust of the area was subjected to a stress which transmitted from the outer regions toward the epicentral area and then back.