用重力测量技术观测城市地表下沉的实验研究

Experimental study of the surface subsidence in the city using gravity observing techniques

本文用重力测量技术对城市地表下沉进行了实验研究,从2016年3月到2017年5月在武汉市内地表下沉较大的部分城区进行了7期流动重力观测实验,并用D-InSAR观测的垂向位移进行了验证.数值结果表明重力观测每期整网平差后点值平均精度都小于10×10^-8 m·s^-2,说明采用重力观测能在城市内获得高精度的区域重力变化.第7期相对于第1期的结果与D-InSAR在大致相同时间段内地表垂直位移结果比较表明,重力增加的大部分区域与D-InSAR观测到的地表下沉区域相一致,说明这些区域的重力增加主要是由地表下沉引起的.从第2到7期相对于第1期的重力变化说明在近12个月的时间内测区最大重力变化约40×10^-8 m·s^-2,且局部区域的重力值是逐渐增加的,说明地表下沉是持续进行的.本实验结果说明重力观测技术能为城市地表下沉提供重力观测约束和机制解释.

Experimental study of the surface subsidence in the city using the gravity observing techniques is carried out in the paper.There are 7 gravity campaigns at regions with comparatively large surface subsidence in Wuhan city,China.The gravity results are finally verified by the vertical displacements observed by D-InSAR.Numerical results show that the point-value mean accuracies after the whole network adjustment for all the 7 gravity campaigns are all smaller than 10×10^-8 m·s^-2,which indicates that high-accuracy regional gravity variations can be obtained by gravity measurements.The gravity change between the 7 th and the 1 st campaign is compared with vertical displacements observed by D-InSAR in almost the same time interval.The comparison shows that most of the regions with increased gravity change are coincided with those that have surface subsidence observed by D-InSAR,which accounts for the gravity increase mainly induced by the surface subsidence.The largest gravity change obtained from the 1 st campaign to the 2 nd and 7 th ones reaches about 40×10^-8 m·s^-2 in about 12 months.And the surface subsidence is a continuous variation because some regional gravity values are gradually increasing.Results in the study show that gravity observation techniques can provide gravity constrain to the surface subsidence in the city and the subsidence mechanism explanation.