Present-day land subsidence rates, surface faulting hazard and risk in Mexico City with 2014–2020 Sentinel-1 IW InSAR

Abstract

Among the fastest sinking cities globally, the metropolitan area of Mexico City is the target of an unprecedented satellite investigation based on over 300 Sentinel-1 Synthetic Aperture Radar (SAR) Interferometric Wide swath mode scenes acquired in 2014–2020. Two-pass differential Interferometric SAR (InSAR) and the parallelized Small BAseline Subset (SBAS) repeat-pass InSAR approach provide a complete account of spatial patterns, long-term trend and present-day settlement rates affecting the city. The 3D deformation field reveals that foremost is the role of the vertical velocity VU, with peaks of −38.7 cm/year in Nezahualcóyotl, −32.0 cm/year in Gustavo A. Madero and Venustiano Carranza, and −39.1 cm/year in Iztapalapa. Settlement at the metropolitan Cathedral in Cuauhtémoc is ongoing at up to −8.8 cm/year, consistently with the last six decades. Volcanic edifices mark ground stability “islets” inside the main subsidence bowls. East-west rates are limited, except for some horizontal strain (up to ±5 cm/year) within the subsidence bowls. Comparison with surface geology and geotechnical zoning confirms that aquitard compaction is the predominant process. The power relationship between VU [cm/year] and the thickness of lacustrine clay deposits HC [m] is: VU=176∗HC1.8. The 2019–2020 deformation scenario shows that subsidence still involves most of Nezahualcóyotl, with −3.0 cm/month VU. A well-defined long-term deformation behaviour comes out from 2014–2019 InSAR time series and comparison with 2008–2020 GPS data. RMSE of 0.9 cm is found at MMX1 station deployed within the lacustrine unit, and 0.6 cm at TNGF station onto hard volcanic rocks. The sharpest subsidence gradients and angular distortions β in 2017–2019 (up to over 1/400, i.e. 0.14°) – thus the greatest vulnerability to surface faulting and cracking as a consequence of large tensile stress in the soil caused by differential settlement – are found at the foothills of Sierra de Santa Catarina, Peñón del Marqués, Cerro Chimalhuachi, Peñón de los Baños and Sierra de Chichinautzin, where the transition unit is narrower (or absent). Faults and cracks develop where β > 1/3000, i.e. 0.03%, in 2017–2019. The observed width of the influence zone (i.e. damage band), where β is still significant to induce damage, is 250 m. Differential settlement and surface faulting could compromise the serviceability of housing and utility infrastructure. It is estimated that over 457,000 properties and 1.5 million inhabitants of the Valley of Mexico Metropolitan Area (ZMVM) are in zones at high to very high surface faulting risk, mainly in Iztapalapa, Tláhuac, Chimalhuacán and Chalco. Increased flood exposure due to formation of topographic depressions involves over 751,000 properties and ~2.7 million inhabitants of the ZMVM, mainly in Nezahualcóyotl, Tláhuac, Venustiano Carranza, Iztapalapa, Gustavo A. Madero and Ecatepec de Morelos. These municipalities are often hit by catastrophic floods.