The spatial distribution characteristics of noise level based on the gPhone gravimeters

Abstract:

Ocean storms are strong, local atmospheric disturbances and contain amounts of energy, which can be transferred from atmospheric energy to ocean gravitational wave energy. This is then partly transferred to elastic energy by interaction with the seafloor. Such elastic energy can make its footprint on seismic records and is part of recorded seismic noise. Research on seismic noise can be traced back as early as 1900s and was mainly focused on long-period noise called Earth’s background free oscillations, or so called Earth’s hum(2-7mHz) and relatively short-period noise microseisms(0.05-0.5Hz). Both Earth’s hum and microseisms are actually ground motions recorded by seismic stations. Now a day, many 1Hz gPhone gravimeters have been located at some seismic stations and observed these ground motions recorded in Chinese mainland.

So in this paper, Firstly, the 1Hz datum of the WUSHI seismic stations have been analyzed with wavelet and tidal correcting. It is shown that the noise level calculated by the db4 wavelet and larger 2 level are similar with the tidal corrected method. And the noise level which are estimated with the standard deviation of the gravity residual each day, shown the year periodic change. In spring and winter, the noise level is almost largest, and reaches the minimum in the summer. The noise level is about 10±5×10^-8ms^-2. Secondly, from 2007 to 2008, more than 2 years datum of 12 gPhone gravimeters are analyszed along with co-located each other by wavelet method. It is shown that, in Fig 1, there are only 1-3 ×10^-8ms^-2 difference amount all the gPhone gravimeter noise leve at the same time and more than 95% of the correlation amount all the time series of gPhone gravimeters noise level. So, at last, by analysized the station type and the noise level of the 12 seismic stations with gPhone gravimeter, it is shown that, the noise level of the cave stations is smaller than the basement or surface station’s. And the noise level near the coastline is greater than the western one. There are the half year period at the Tibet area.