The Preliminary Analysis To The Non-tidal Variations Of Continuous Gravity Observations In Mainland China

With the developing of the project---The Monitoring Network of Continental Tectonics in mainland China, also the ongoing of the Digitized Observation Network of Earthquake Precursor, a monitoring network on earth’s activities has been established over the country. Gravity is one of the important observed technologies, and the network of tidal gravity stations in mainland have been built up gradually during this period, there were more than50stations have been put into working until January2012, widely distributed in mainland China, which were providing valuable observed datasets. The researches of continuous gravity observations in stations have focused on tidal theory and tidal analysis as so far, which have made many important achievements and promoted the development of related fields. Therefore, based on the datasets from the network of gravity stations, the paper expanded analysis and researches of non-tidal gravity information.For preprocessing of continuous gravity data, we used the latest tidal data pre-process software TSOFT, which was recommended by the International Center of Earth Tide (ICET) as the standard software in tidal data preprocessing, to replace the traditional method which with low precision. We used the TSOFT software to clear away different kinds of interferences, such as spikes, gaps, steps and earthquake events, from the original continuous gravity datasets of28stations in past3.5years (2008.1～2011.5). Meanwhile, considered the biggish influence of the meteorological to gravity observations, we calculated the atmospheric loading effects through single coefficient of atmospheric gravity admittance. Based on the continuous and smooth gravity observations after preprocessing, we claimed a new process to deal with the complex and multiple drift in the observations, which was called Sectional Curve Fitting based on the preprocessing software---TSOFT, then gained the observations which were consistent with the theoretical tidal gravity value. After that, we used the Pertesv’s Filtering, which was powerful in filtering out tidal components from the hour sample observations, to extract the non-tidal gravity signals, which were the regional continuous gravity changes of the stations.To verify the reliability of the non-tidal gravity signals above, we introduced the GRACE satellite gravity results to compare the magnitude and trends of the non-tidal gravity signals. Furthermore, for analysis of the main signal contained in the results, and considering the key role terrestrial water palyed in the field gravity changes, we introduced datasets of the CMAP terrestrial water model, made correlation analysis of them. At last, took the tidal gravity observations of Beijing BJT station as example, estimated the power spectral density of related tidal observations, analyzed the frequency components of related tidal observation, meanwhile, compared and analyzed the effectiveness and capacity of Pertesv’s Filtering on filtering out the tidal components from continuous gravity observations. Besides, we tried to extract the ground quake events from original gravity observations through the software TSOFT, and compared them with the earthquake catalog.The main results of this paper were:1) As a standard tidal pre-process software, TSOFT was powerful in dealing with various types of interferences in continuous gravity observations, which was worthwhile to promote use in pre-processing of tidal observations.2) Sectional Curve Fitting was effective in dealing with the complex and multiple drift in the gravity observations.3) The non-tidal gravity signals were with high precision, most of those were better than10μGal. Besides, the non-tidal gravity signals were consistent with the results of GRACE, which means the non-tidal results were reliable.4) The terrestrial water was one of the main factors of the field gravity variations, and the field gravity changes delayed about1---2months after the terrestrial water changes.5) The power spectral density of related gravity observations showed that Pertesv’s Filtering was powerful in filtering out tidal components from the hour sample observations.6) The ground quake events extracted from original tidal gravity observations through the software TSOFT, were accordant with the earthquake catalog.