Khorrami Mohammad, Abrishami Saeed, Maghsoudi Yasser, Alizadeh Babak, Perissin Daniele
Department of Civil Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran.
Department of Civil and Coastal Engineering, University of Florida, Gainesville, FL, 32611, USA.
Sci Rep. 2020 Jul 9;10(1):11357. doi: 10.1038/s41598-020-67989-1.
Ground deformation can cause serious environmental issues such as infrastructure damage, ground compaction, and reducing the ground capacity to store water. Mashhad, as one of the largest and most populated cities in the Middle East, has been suffering from extreme subsidence. In the last decade, some researchers have been interested in measuring land subsidence rates in the Mashhad valley by InSAR techniques. However, most of those studies were based on inaccurate measurements introducing uncertainties in the resulting subsidence rates. These researches used a small number of EnviSat data with long perpendicular and inhomogeneous temporal baseline. This paper seeks to determine the subsidence rate in urban areas of Mashhad in recent years, the threat that was neglected by the city managers and decision-makers. For this purpose, the Persistent Scatterer InSAR technique was applied in the study area using two time-series of descending and ascending Sentinel-1A acquisitions between 2014 and 2017. The results demonstrated the maximum line-of-sight deformation rate of 14.6 cm/year and maximum vertical deformation (subsidence) rate about 19.1 cm/year which could have irreversible consequences. The results were assessed and validated using piezometric data, GPS stations, and geotechnical properties. This assessment confirms that the main reason for subsidence in the interested area is groundwater over-extraction. Also, investigation of geotechnical properties shows that thick fine-grained layers in the northwest of the city could strongly affect the results. At the end of this paper, a new simplified method was proposed to estimate specific storage in special cases to predict the subsidence rate.
地面变形会引发严重的环境问题，如基础设施损坏、地面压实以及降低地面蓄水能力。作为中东地区最大且人口最多的城市之一，马什哈德一直饱受极端沉降之苦。在过去十年中，一些研究人员一直致力于利用合成孔径雷达干涉测量（InSAR）技术测量马什哈德山谷的地面沉降速率。然而，这些研究大多基于不准确的测量，导致所得沉降速率存在不确定性。这些研究使用了少量具有长垂直基线和不均匀时间基线的环境卫星（EnviSat）数据。本文旨在确定近年来马什哈德市区的沉降速率，而这一威胁此前被城市管理者和决策者所忽视。为此，在研究区域应用了永久散射体InSAR技术，使用了2014年至2017年间两次 Sentinel - 1A 降轨和升轨采集的时间序列数据。结果表明，最大视线变形速率为每年14.6厘米，最大垂直变形（沉降）速率约为每年19.1厘米，这可能会产生不可逆转的后果。利用测压数据、全球定位系统（GPS）站和岩土特性对结果进行了评估和验证。该评估证实，研究区域沉降的主要原因是地下水过度开采。此外，对岩土特性的调查表明，该市西北部的厚细粒层可能会对结果产生强烈影响。在本文结尾，提出了一种新的简化方法，用于在特殊情况下估算比储水率以预测沉降速率。
