Results of Gravity Observations Using a Superconducting Gravimeter at the Tibetan Plateau

Abstract

The tidal and nontidal gravity change characteristics in the Tibetan Plateau region were investigated using the continuous gravity measurements recorded with a superconducting gravimeter (SG) installed in Lhasa from December 8, 2009 to September 30, 2011. The results indicated that the precision of the tidal gravity observations with the SG in Lhasa was very high. The standard deviation of the harmonic analysis for the gravity tides was 0.498 nm s -2 , and the uncertainties of amplitude factors in the four main tidal waves (i.e., O 1 , K 1 , M 2 and S 2 ) were better than 0.002%. In addition, the diurnal gravity tide observations clearly revealed a pattern of nearly diurnal resonance. As a result, it is affirmed that the station should act as a local tidal gravity reference in the Tibetan Plateau and its adjacent regions. The load effects of oceanic tides are so weak that the resulting perturbation in the gravimetric factors is less than 0.6%. However, the load effects of the local atmosphere on either the tidal or the nontidal gravity observations are significant, although no seasonal variations have been found. After removing the atmospheric effects, the standard deviation of the harmonic analysis for the gravity tides decreased obviously from 4.160 to 0.498 nm s -2 . Having removed the load effects of oceanic tides and local atmosphere, it is found that the tidal gravity observations are significantly different from those expected theoretically, which may be related to active tectonic movement and extremely thick crust in the Tibetan Plateau region. In addition, the Earth's free oscillations excited by 2011 Tohoku-Oki M w 9.0 Earthquake were successfully detected.

Influences of the Tibetan plateau on tidal gravity detected by using SGs at Lhasa, Lijiang and Wuhan Stations in China

“…The tidal gravity results are given here for the first time for station Lijiang. We also found that the tidal gravity parameters determined in Lhasa and Wuhan were in good agreement with those obtained in previous studies (Sun et al 2005b(Sun et al , 2013Wei et al 2012;Xu et al 2012Xu et al , 2014. Compared with the previous findings in Lhasa, the amplitude factors δ of the main tidal waves were about 0.8% larger as a result of evaluation bias in the scale factors in the previous studies, whereas the phase differences Δφ were nearly consistent.…”