Multi-temporal interferometric monitoring of ground deformations in Haiti with COSMO/SkyMed HIMAGE data

The catastrophic Mw=7.0 shallow earthquake of 12 January 2010 that struck Haiti have led to numerous studies focused on the geodynamics of the region. In particular, the co-seismic fault mechanism of the 2010 Haiti earthquake as well as post-seismic deformations have been investigated through SAR interferometry (InSAR) techniques, thanks to the availability of satellite SAR sensors operating in different radar bands (ENVISAT ASAR, ALOS PALSAR, TerraSAR-X, COSMO/SkyMed). Moreover, advanced multitemporal SAR interferometry (MTI) based on COSMO/SkyMED (CSK) data is well suited for the detection and monitoring of post-seismic ground or structural instabilities. Indeed, with its short revisit time (up to 4 days) CSK allows building interferometric stacks much faster than previous satellite missions, like ERS/ENVISAT. Here we report the first outcomes of the MTI investigation based on high resolution (3 m) CSK data, conducted in the framework of a scientific collaboration between the Centre National de l'Information Géo-Spatiale (CNIGS) of Haiti and the Department of Physics (DIF) of the University of Bari, Italy. We rely on a stack of 89 CSK data (image mode: HIMAGE; polarization: HH; look side: right; pass direction: ascending; beam: H4-0A) acquired by the Italian Space Agency (ASI) over the Port-au-Prince (PaP) metropolitan and surrounding areas that were severely hit by the 2010 earthquake. CSK acquisitions span the period June 2011 ÷ February 2013, which is sufficient for detecting and monitoring significant ground instabilities. The MTI results were obtained through the application of the SPINUA processing chain, a Persistent Scatterers Interferometry (PSI)-like technique. In particular, we detected significant subsidence phenomena affecting river deltas and coastal areas of the PaP and Carrefour region. The maximum rate of subsidence movements exceed few cm/yr and this implies increasing flooding (or tsunami) hazard. Furthermore, maximum subsidence rates were encountered in areas with high population density and this translates into high potential risk. The MTI results also revealed the presence of very slow slope movements and local ground / structure instabilities. Some of these may have been initially triggered by the 2010 event. Elsewhere the MTI-detected displacements can be related to the presence of poorly constructed buildings. This case study demonstrates that MTI represents a very good option for the assessments of ground / structure instability in regions that lack in situ monitoring data. In view of this the results of this study will be transferred to the Civil Protection of Haiti.