Evolution assessment of structurally-controlled differential subsidence using SBAS and PS interferometry in an emblematic case in Central Mexico

The city of Morelia has been affected by Structurally-Controlled Differential Subsidence (SCDS) since at least 1983, modifying civil structures and infrastructure through the appearance of ground failures and differential ground subsidence. The resulting damage to streets, homes, hydraulic lines, and government facilities has caused economic losses worth millions of dollars. An increase in population has led to the overexploitation of groundwater, which is the main trigger for SCDS, while the subsoil's geology and bedrock configuration are considered conditioning factors of this phenomenon. This paper offers an analysis of the SCDS evolution over the last fourteen years and its relationship with groundwater extraction and thickness of unconsolidated sediments. The former was carried out through SAR Interferometry techniques to detect and monitor land subsidence, using Small Baseline Subset (SBAS) from 2003 to 2010 and Persistent Scatterer Interferometry (PSI) from 2014 to 2017. Additionally, groundwater pumping well data and lithological information from boreholes enabled a spatial analysis to evaluate the role of these factors in the development and acceleration of SCDS. The SBAS results show maximum sinking rates of 2.2 cm/yr. with a spatial distribution that is clearly controlled by buried geological structures. In this period, the maximum sinking rates were induced by high groundwater extraction rates in focused areas, while intermediate rates were linked to notable depletion cones. The PSI results indicate a maximum sinking rate of 2.74 cm/yr. and an accelerated subsidence migration to the west, owing to the construction of new wells and persistent high groundwater extraction rates. For both periods, the larger compressible sediment package reveals a good correlation with high subsidence rates, mainly in the hanging wall blocks of the buried faults. The identification of differential subsidence accompanied by high sinking rates in novel areas of Morelia, as well as the detection of the subsidence migration, will provide scientific support to decision-makers for the proposal of engineering solutions and urban planning capable of reducing hydrogeological hazards associated with SCDS.