不同地球模型对中国陆区大气负荷位移建模的影响

The influence of different earth models on atmospheric load displacement modeling in Chinese continent

目前进行质量负荷位移建模时通常使用的是全球或区域平均的一维地球模型,这类地球模型无法反映地壳结构的局部差异,如地壳厚度、地震波波速等.本文利用地表气压再分析数据产品NCEP/NCAR Reanalysis 1(NCEP R-1)和不同地球模型(Preliminary reference Earth model(PREM)、AK135、STW105和CRUST1.0)计算的负荷格林函数计算中国陆区的大气负荷垂向形变,结合GPS实测位移数据,评估基于不同地球模型计算得到的地表形变的差异.通过比较PREM与不同地球模型的建模结果发现,一维地球模型之间的建模差异较小,主要集中在气压变化较大的东部地区和西北地区,气压变化较小的青藏高原地区的建模差异则更小.相反,PREM与CRUST1.0模型在青藏高原地区的建模差异最大,在东部地区的建模差异最小.PREM与STW105、AK135和CRUST1.0在中国陆区的最大位移建模差异分别为0.05、0.34和0.44 mm.不同地球模型的建模差异是由负荷格林函数不同产生的,而负荷格林函数在近场受上地壳厚度的影响较大.对于局部地壳结构差异明显的青藏高原地区,一维地球模型AK135和STW105的建模结果对GPS残差的修正效果与PREM相当,而CRUST1.0地壳模型在修正PREM后可以使残差的WRMS最高降低0.93%.本文的研究表明,地壳结构的局部差异对负荷位移建模的影响不容忽视.

Usually, the globally or regionally averaged 1D Earth models are used for modeling mass loading, which cannot reflect the regional deviations of crustal structures, such as the thickness of crust, seismic wave velocity, etc. We use the reanalysis surface pressure product NCEP R-1 and the load Green′s functions computed by different Earth models(PREM, AK135, STW105 and CRUST1.0) to model the vertical displacements caused by global atmospheric mass loading in Chinese continent. Besides, we evaluate the discrepancy of modeling atmospheric mass loading by combining GPS-measured displacement data. The results show that the modeling differences among 1D Earth models are small, not only in eastern and northwestern China, where the surface pressure changes greatly, but also in the Qinghai-Tibet Plateau, where the surface pressure changes are small. However, the differences between PREM and CRUST1.0 models are large in the Qinghai-Tibet Plateau and small in eastern China. The maximum of modeling differences between STW105, AK135, CRUST1.0 and PREM in Chinese continent are 0.05, 0.34 and 0.44 mm, respectively. The modeling discrepancies between different Earth models depend on the load Green′s functions. Especially, the load Green′s functions in the near field are affected by the thickness of the upper crust. For the Qinghai-Tibet Plateau, where the deviation in local crustal structure is obvious, the corrections of atmospheric mass loading using the AK135 and STW105 Earth models to GPS residuals are about the same as PREM, but 3D Earth model CRUST1.0 can reduce the WRMS residuals by up to 0.93%. Our results imply that the local differences of shallow crustal structure should be considered when modeling load displacement.