Abstract:The practice and experiments for many years have proved that the calibration of the gravimeter varies with temperature and has great effect on observed values. So it is necessary to find the temperature coefficent of the calibration and to correct the calibration of the observation data.
In this article, the calibration of all gravity data in Beijing, Tianjin and Tangshan regions has been corrected in another way. After the correction, the annual variation of gravity values at various stations is obviously eliminated, and has been calculated pre-earthquake gravity anomaly in Tangshan.
From April, 1974 to March, 1976, the cumulative gravity increased by 130μgal and the short-term anomaly approached 200μgal.
The obtained results show that. the pre-earthquake gravity variation may due to the density anomaly at deep levels of the earth's crust.