关键词: 中强地震, 倾斜形变潮汐, 短临异常

Abstract: An analysis has been made of the 2005 earth tide observation data recorded by the CZB-1 type perpendicular pendulum tiltmeter at the Yanshou Seismic Station of Heilongjiang,using the two day(48h)and two-day sliding monthly harmonic analysis method.Values of the tidal factor γ and the phase-delay factor Δφ before the Jul 25^th,2005 M_S 5.1 Lindian,Heilongjiang and the Sept 19^th 2005 M_S 4.7 Yakeshi,Inner Mongolia earthquakes have been determined for the semidiurnal constituent(M₂)of the tilt earth tides.As a result,some features of deformation of tide variations prior to some moderate earthquakes have been revealed.Relation expression was preliminarily calculated between the waiting time after anomaly or anomaly amplitude or epicentral distance and earthquake magnitude.Results of comprehensive analysis are as follows:(1)The tidal factor reflects the elastic stage of earth crust media response to tidal force in physical meaning.The earth crust media state varies and the earth crust deformation turns into an instable phase along with stress strengthening before moderate-strong earthquake.Adopting the harmonic analysis method and with a proper calculation length,the anomaly information of the tidal factor and the phase-delay factor are extracted for better analyzing and calculating the stress-strain state of earth crust media against the time series,giving prominence to the short-impending anomaly information,and catching the precursor anomaly of earthquake occurrence.(2)Tidal factor variations reflect the stress change in earth crust media of seismic source area,which offers the short-impending precursor information relating to time.The variation process can be summarized as trend background → augmentation or contraction → extreme → restitution → waiting → earthquake occurrence.(3)The harmonic analysis method of tide has high anti-interference ability.It can remove the interferences,such as the long-term trend drift and environmental effect,to provide stable figures and give prominence to the anomaly information.In addition,the Venedikov harmonic analysis method is a valid method for studying the relationship between the tidal tilt anomalies and the moderately strong earthquake.

Key words: moderate strong earthquake, tilt earth tide, short-impending anomaly