川西地区实测自由空气重力异常与EGM2008模型结果的差异

在四川盆地西部建立了一个由302个观测站组成的区域观测网,并进行了高精度流动重力与GPS观测,其目的是获取区域自由空气重力异常(简称重力异常)的分布特征,并对EGM2008模型在该区域的结果进行验证分析.研究区域实测的重力异常总体为负值,由西到东逐步从-160×10^-5ms^-2平缓变化到-60×10^-5ms^-2左右.EGM2008地球重力场模型揭示的模型重力异常较好地勾画出研究区域的总体地形分布形态,龙泉山脉以及四川盆地与青藏高原的边界皆存在明显的模型重力梯度带.研究区东南部的模型重力异常大约为-50×10^-5ms^-2左右,但在龙泉山西部成都平原地区,模型重力异常则达到-120×10^-5ms^-2左右.在区域观测网内绝大部分观测点上,模型与实测重力异常的差值几乎为一个常数(-10×10^-5ms^-2左右),说明EGM2008地球重力场模型可较好地反映实际重力场的空间分布形态.如果配以一定数量的地面观测数据进行整体调节,EGM2008地球重力场模型就可以较真实地反映实际地球重力场.

Discrepancies between free air gravity anomalies from EGM2008 and the ones from dense gravity/GPS observations at west Sichuan Basin

Recently we built a dense regional observation network, which is made up of 302 stations, at the west of Sichuan Basin, and carried out a gravity/GPS hybrid observation campaign. The aim is to get the detailed features of the Free-air Gravity Anomaly (FGA) at the study area, and to evaluate the quality of the modeled results of EGM2008. As a whole the observed FGAs are negative. They change slowly from about -160×10^-5ms^-2 at west to -60×10^-5ms^-2 at east of the study area. The modeled FGAs from EGM2008 consist well with the topography of the west of Sichuan Basin. There exist visible modeled gravity gradient belts at both Longquan Mountain and the boundary of Sichuan Basin and Tibetan Plateau. At the southeast of the study area the modeled FGAs are about -50×10^-5ms^-2. However, at the Chengdu plain to the west of Longquan Mountain, the modeled FGAs become as large as -120×10^-5ms^-2 or so. The discrepancies between the modeled FGAs and the observed ones change slightly round -10×10^-5ms^-2 at most points of our observation network, indicating that the EGM2008 can recover the total distribution shape of the earth gravitational field in the study area. If adjusted by a number of observation results in situ at the earth's surface, the EGM2008 will reflect well the real gravitational field of the earth.