ANALYSIS TO THE DATA OF VERTICAL PENDULUM GROUND TILTMETER IN YANSHOU SEISMOSTATION OF HARBIN CITY

The working status of vertical pendulum tiltmeter in Yanshou Seismostation of Harbin is introduced,and several earthquake strain steps recorded by the instrument are presented.The results show that this kind of steps reflects the variation of crustal strain field caused by earthquakes.From the image of steps we can see that the magnitude of step is relatively small for medium and strong remote earthquake,and is large for near earthquakes.The epicentral distance smaller,the magnitude larger for the same magnitude earthquakes.It indicates the influence of near earthquake to local strain field is larger than remote earthquake.Through analysis to short term and imminent anomalies before Lindian M5.1 earthquake that occurred on Jul.25,2005,we found that shape of short term anomaly was very similar to the imminent one,but the response of one component observation to the two anomalies was different,which may be relevant to the adjustment of crustal strain field in different stage of earthquake development.