芦山M_S7.0地震震前GRACE卫星时变重力场特征研究

Characteristics of gravity field before the Lushan M_S 7.0earthquake based on time variable gravity data from GRACE satellite

基于GRACE卫星时变重力数据,利用小波多尺度分解方法,分析研究了芦山MS7.0地震前重力场的时空动态演化特征.结果表明,雅安地区震前卫星时变重力场具有明显的重力变化信息.卫星时变重力场在时间域表现为,累积重力场和差分重力场存在较强的规律性动态变化,以2003—2004年均值为基值的2009—2012年的变化特征与2005—2007年的变化特征具有较好的相似性,以2009年均值为基值的2009—2012年即芦山地震前4年,芦山震区的时变重力场呈现上升→减速上升→加速上升以及上升→轻微下降→快速上升的变化特征;卫星重力场在空间域表现为,震中位置由靠近重力场正变化的中心→接近重力场正变化边缘→接近重力正变化四象限分布中心的变化特征.因此,芦山地震的重力场动态变化信息和波场分离结果符合逆冲推覆兼走滑型地震引起的区域变形特征.

Based on monthly gravity data from GRACE satellite, this paper ana lyzes the characteristics of dynamic changes in gravity field before the Lushan MsT. 0 earthquake by multi-scale wavelet decomposition method. Results show there is a regulation of the dynamic variations in the cumulative gravity field and differential ones. In the time domain, taking the annual average value of gravity field in 2003--2004 as the base value, the annual variation characteristics of gravity field in 2009--2012 are similar to those in 2005--2007. On the basis of the annual average value of gravity field in 2009, the annual changes in gravity field from 2009 to 2012 exhibit a process, i. e., increasing → decelerated increa- sing →accelerated increasing or increasing → slightly descending → rapidly in- creasing. In the spatial domain, the positive gravity variations are characterized by the process that the epicentral location moves from the center of positive gravity variations to its border, and then to the center of the four-quadrant dis- tribution. So dynamic changes in the gravity field and wave field separation re- sults of the Lushan Ms7.0 earthquake are consistent to the regional deformation characteristics resulted from the Lushan earthquake as a thrust-nappe and strike-slip earthquake.