关键词: 震源非线性, 地震前兆, 地震预报

Abstract: Earthquake focus system is a dissipative system which continuously exchanges energy and mass with outside. There will be a series of bifurcations in the process of earthquake preparation. The precursors of 1975 Haicheng earthquake in Northeast China and 1976 Tangshan earthquake in North China are studied with nonlinear dynamic method. There are 5 similar precursor stages for the two earthquakes. The durations reduced sequentially from the first stage to the fifth stage. The ratio of the durations of the two adjacent precursor stages is a constant (about 5). Five stages bagan about 2.5 years, 5.5 months, 1 month, 6 days and 1 day separately before the earthquake occurred.The main precusor features are: (1) gravity anomaly, (2) strain and stress conversion or jump at the background of strain and stress anomaly, (3) anomaly of the groundwater in very large region, (4) great variation of the air temperature and the geotemperature, the fluctuation of air pressure and the abnormal behaviors of domestic animals, and (5) eaarthquake lighting, earthquake sounds frequently and seriously disturbed radiowave.This relationship of precursor stages resulted from the period-doubling bifurcations in earthquake focus body with the increase of earthquake preparation time. Each grade bifurcation point corresponds to one precursor stage start time. The ratio of the durations of two adjacent precursor stages approximates to well-known Feigenbaum number (4.67). According to this relationship, we can predict the start time of later precursor stages and main shock time when two or more precursor stages are known.

Key words: Nonlinear focus, Earthquake precursor, Earthquake prediction