THE EVOLUTIVE CHARACTER OF FIXED LEVELING ANOMALY

Based on Zhangbei earthquake occurred on Jan.1, 1998, the character of fixed leveling anomalies observed in Kuancheng, Xinglong and Yixian Seismostation are analyzed.As the data of fixed leveling have annual period, so we must eliminate its annual variation before analyzing its anomaly.After processed with periodical filtering method we find fixed leveling anomalies have different phases in development, which can be divided into early term, medium term and imminent term three stages, and it has distinct sign turning from medium term into imminent term.