Urban areasIn contrast to the preceding test sites, Mexico City is characterized by extremely large rates of vertical subsidence. Since 1950, several areas show accelerated ground motions, reaching today 35 cm/yr, and developed associated fractures (Cabral Cano et al., 2007). The subsidence is primarily controlled by compaction of Quaternary lacustrine clays and silts, deposited in the emplacement of the former lake Texcoco located in Mexico Valley basin. Large horizontal subsidence gradients occurring along the former lake shores, at the piedmont of hills within Mexico City, can produce considerable damage to building and infrastructure. The PhD work of P. Lopez-Quiroz is to analyse existing SAR images (19 ERS and 35 Envisat images on a single track/frame) by interferometry to map ground subsidence through space and time, in order to relate spatial and temporal changes in subsidence rate to meteorological events, water pumping fluctuations, infrastructure modifications. P. Lopez-Quiroz will address in particular the relation between ground motion and seasonal basin groundwater recharge by water flow from surrounding mountains. Specific methodological developments must be carried to extract from the entire data stack reliable deformation time series (from 1995 to 2006), due to phase unwrapping difficulties. Besides testing the PS software developed by Hooper (Hooper et a., 2004, WP3), we will implement a small baseline approach with a specific unwrapping procedure adapted to the area (WP4). Furthermore, we will use image amplitude correlation techniques (WP5) to measure the integrated 1995- 2006 displacement field, which can bring complementary information to the DinSAR time series. Mitigation of atmospheric artefacts as proposed in WP6 will allow a more accurate estimation of ground subsidence. |