Monitoring Ground Subsidence in the Modern Yellow River Delta Based on SBAS Time-series Analysis

Land subsidence in the modern Yellow River Delta at high spatial and temporal resolution was deduced from SBAS time-series analysis of ERS1/2 data. The experimental results show that land subsidence in the modern Yellow River Delta is widespread and unevenly distributed with large differences. The average subsidence rate is -5.1 mm/yr, while the highest subsidence rate of -33.2 mm/yr occurring in the subsidence funnel formed by an oil field. The InSAR results are shown to be reliable, when compared with leveling survey measurements. Ground based leveling measurements included 53 leveling points were used to evaluate the accuracy of our SBAS time-series analysis results with a consistent deformation trend between the two sets of results. A comparison between leveling points and their nearest SBAS points at the same time interval showed they were in complete agreement, while the mean square error between them was at the mm level. The main influencing factors differ by region. Severe land subsidence however, is caused by oil extraction including extracting nearby shallow groundwater used for artificial water injection after oil exploitation and sediment consolidation. Oil exploitation was the main influencing factor and responsible for the rapid, patchy subsidence evident at Dongying city, Hekou district, Gudao town, Zhuangxi, and the Gudong oilfield. Groundwater extraction for making salt and oilfield water injection is likely responsible for land subsidence in the Liuhu township and at the Guangrao salt pan. Increased surface load aggravated land subsidence in the old urban district of Dongying city, and sediment consolidation might be considerable after the lobe is abandoned.