Abstract:Research has showed gravimetric satellite GRACE can detect the coseismic geoid and gravity changes induced by a megathrust earthquake. In this paper, we use a de-correlation filter of DDK3 to smooth the GRACE RL06 data released by Center for Space Research(CSR). By using time series analysis based on least square approach, we successfully extract the coseismic gravity, geoid, vertical deflection and gravity gradients changes caused by the 2004 Sumatra MW9.3 earthquake, the 2010 Chile MW8.8 earthquake and the 2011 Tohoku-Oki MW9.0 events. The results show that the range of coseismic gravity of the three earthquake cases are -15.5 to 6.5 μGal, -9.1 to 2.1 μGal and -11.1 to 4.2 μGal, respectively. The range of coseismic geoid is -5.9 to 0.8 mm, -3.0 to 0.8 mm and -3.2 to 0.5 mm. The variation range of north-south vertical deviation is -1.2 to 2.2 mas, -0.9 to 1.0 mas and -1.1 to 1.4 mas. The east-west variation ranges are -1.8 to 1.0 mas, -0.8 to 0.8 mas and -0.7 to 1.0 mas. Among the components of the gravity gradient, the coseismic variation of rr component is the largest, followed by the variation of the rθ component. The spatial distribution of coseismic signals of the three earthquakes is as follows, the coseismic geoid and gravity change signals are distributed asymmetrically at two poles. The vertical deviation is negative-positive-negative or positive-negative-positive three-pole distribution; the signal of gravity gradient change presents a complex multipole distribution. Our GRACE coseismic signals agree well with some theoretical models better than others. The time series analysis method in this paper is robust and can be used to obtain the co-and post-seismic geodetic deformations and gravity field changes which is often used to constraint the fault slip and Earth’s viscosity structure.
ZHANG Suxiang,SHENG Shuzhong,ZHOU Xin. The Coseismic Gravity Field Variations of Megathrust Earthquakes in the Subduction Zone Measured by Gravity Satellite[J]. jgg, 2021, 41(10): 991-997.