利用海洋重力场变化分析洋底板块运动

Altimeter-derived marine gravity variation studies the submarine plate tectonic motions

洋底板块运动是地球动力学和全球变化研究的重要内容.本文根据质量迁移与地球外部重力场变化的对应关系,利用不同时期测高资料推算的1995-2019全球海洋重力场变化结果,反演分析全球洋底板块运动特征.研究表明,板块汇聚边界、板块内无震海岭、海山群、断裂带等区域重力异常变化显著,而在板块离散边界无明显变化趋势;西南印度洋中脊、大西洋中脊、中印度洋中脊等地区重力异常垂直梯度变化显著,且在西太平洋俯冲带、部分海岭区域也存在明显变化,其空间分布与地形基本吻合.海洋重力场变化整体上准确反映了全球洋底板块构造运动.相较于重力异常变化反演结果,重力垂直梯度的变化能够更为准确地反映洋底板块运动特征,特别是在洋中脊区域,扩张速率越小,垂直重力梯度变化越显著.此外,详细讨论了测高海洋重力场不确定因素对洋底板块运动分析结果的影响,海面坡度改正是主要因素之一.

Submarine plate tectonic motions are important part of geodynamics and global change.In this paper,based on the correspondence between mass migration and change of the earth′s external gravity field,global marine gravity field variations from 1995 to 2019 calculated by the altimetry data of different periods are used to analyze the submarine plate motion characteristics.The results show that the gravity anomalies change significantly at plate convergent boundaries,aseismic ridges,seamount groups and fault zones,but not at plate divergent boundaries.The vertical gravity gradients vary significantly in the Southwest Indian Ridge,Atlantic ridge and Middle Indian Ridge,as well as in the subduction zone of the western Pacific Ocean and some aseismic ridges,which spatial distributions are basically consistent with the terrain.The marine gravity field variations accurately reflected the submarine plate tectonic characteristics on the whole.Compared with gravity anomalies,vertical gravity gradient variations can more demonstrably reflect the submarine plate motions,especially in the mid-ocean ridge.The smaller the spreading rate is,the more significant the vertical gravity gradient variation is.In addition,the effects of the gravity field uncertainties on the results are discussed emphatically,the surface slope correction is one of the major factors.