重力卫星观测俯冲带特大地震同震重力场变化

利用去相关的DDK3滤波器对得克萨斯空间中心（CSR）发布的GRACE RL06月重力场模型数据进行处理，采用多项式拟合时间序列分析方法成功提取了2004年苏门答腊M_W9.3、2010年智利M_W8.8和2011年日本东北M_W9.0三个地震事件的同震重力变化、大地水准面变化、垂线偏差变化及重力梯度变化。结果表明，3个震例的同震重力变化范围分别为-15.5~6.5 μGal、-9.1~2.1 μGal和-11.1~4.2 μGal；同震大地水准面变化范围为-5.9~0.8 mm、-3.0~0.8 mm 和 -3.2~0.5 mm；垂线偏差NS向变化范围为 -1.2~2.2 mas、-0.9~1.0 mas 和 -1.1~1.4 mas，EW向变化范围为 -1.8~1.0 mas、-0.8~0.8 mas和 -0.7~1.0 mas；重力梯度各分量数值中，rr分量同震变化最大，其次是rθ分量。3次地震的同震信号空间分布均表现为：同震大地水准面和重力变化信号呈非对称两极分布；垂线偏差呈负-正-负或正-负-正三极分布；重力梯度变化信号呈较复杂的多极分布。观测结果与现有的球体位错理论计算结果较一致，可作为重力卫星数据约束震源机制和地球粘度结构的可靠信号来源。

The Coseismic Gravity Field Variations of Megathrust Earthquakes in the Subduction Zone Measured by Gravity Satellite

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 M_W9.3 earthquake, the 2010 Chile M_W8.8 earthquake and the 2011 Tohoku-Oki M_W9.0 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.