Land subsidence in central Mexico and Indonesia: Differences and Similitudes from Regional ALOS Time-series Surveys
Chaussard, Estelle1; Wdowinski, Shimon1; Amelung, Falk1; Cabral-Cano, Enrique2; Abidin, Hasanuddin3; Hong, Sang-Hoon4
1University of Miami, RSMAS, UNITED STATES; 2Universidad Nacional Autónoma de México, MEXICO; 3Institute of Technology Bandung, INDONESIA; 4Korea Aerospace Research Institute, KOREA, REPUBLIC OF
Massive groundwater extraction is common both in Mexico and Indonesia and is suspected to result in well spread land subsidence. However, most surveys dedicated to land subsidence focus on one single city and thus fail to provide a comprehensive picture of the problem. Here we use InSAR SBAS time series analysis to monitor land subsidence in the entire central Mexico and western Indonesia areas. We used data from ALOS, processed over 1600 SAR images acquired between 2007-2011 and produced over 6000 interferograms. In central Mexico we identify land subsidence in twenty-one areas, including seventeen cities. Subsidence rates of 30 cm/yr are observed in Mexico City, while in the other locations typical rates of 5-10 cm/yr are noticed. In Indonesia we identified subsidence in nine areas, including six major cities, at rates up to 22 cm/yr. We use averaged velocity maps in conjunction with mapping of surface geology and identification of land use to (1) define the activities causing land subsidence, (2) identify the role of stratigraphic features (type of sediments, thickness, and faults), and (3) evaluate the temporal variability of land subsidence. In Indonesia industrial ground water extraction causes rapid land subsidence in cities, whereas outside cities agricultural water extraction is responsible for land subsidence. We do not observe any direct correlation between the distribution of subsidence and surface geology. In Indonesia land subsidence seems rather constant and its main consequence is the direct threat to highly populated coastal areas likely to end up under relative sea level within few decades. In Mexico groundwater extraction for agricultural uses is the main cause of land subsidence, followed by urban use. The subsiding areas are characterized by high velocity gradients often coinciding with existing faults, motion on these faults being driven by water extraction rather than by tectonic activity. Temporal and spatial variability is observed, likely reflecting different stages of the subsidence process. In Mexico the main consequences of land subsidence are ground failure hazards, especially threatening multiple sites of the UNESCO World Heritage list and a decrease in the water quality. Regional surveys of this type are necessary for the development of hazard mitigation plans and efficient use of ground-based monitoring. Sustainability of groundwater resources at regional scale requires the integration of InSAR with other monitoring techniques to understand the aquifer system hydraulic properties.