PREDICTING RAPID URBAN LANDSLIDES IN LA PAZ, BOLIVIA, FROM LOCALIZED, MILLIMETRE-SCALE DEFORMATION DETECTED WITH ADVANCED SPACEBORNE INSAR (Invited Presentation)

La Paz, Bolivia, experiences damaging landslides nearly every year, and the risk they pose will likely increase in the near future due to rapid urban expansion into unstable areas at the city’s periphery. Landslide risk reduction in La Paz requires improved knowledge of where these failures are most likely to happen. Here we describe previously undocumented pockets of localized slow slope deformation that may signal near-future landslides. Homogeneous Distributed Scatterer RADAR Interferometry (HDS-InSAR) combines distributed and point scatterers to provide high-density displacement records that have allowed us to detect and characterize creeping slopes as small as a few city blocks. HDS-InSAR analysis of fine beam mode RADARSAT-2 scenes from 2008 to 2011 reveal slow-moving landslides throughout the city. Most them correspond with large prehistoric landslides in weakly consolidated Pliocene Miocene sedimentary rocks. . Several others are very slow, localized deformation at the sites of at least seven recent damaging landslides. Their sizes (< 4 ha) and rates (~5 mm/a along the line-of-site of the radar) are near the threshold of detection with RADARSAT-2 and would likely not have been identified with conventional InSAR techniques or coarser resolution sensors. The February 2017 landslide in Barrio Auquisemaña occurred at a site with precursor motion on a slope that has been previously mapped as stable. Four landslides in Barrio Retemani between 1997 and 2010 happened at the margins of a zone measuring 140 m by 180 m that had been slowly creeping. Landslides at Seguncoma in 2000 and Huani Hunanuni in 2010 occurred at the lateral margins of similar small zones of very slow deformation. Such zones are important targets for ground-based monitoring and detailed site investigation, even though their exact relationship with rapid failures is yet uncertain. Further HDS-InSAR analysis using recent C-band and X-band RADAR scenes should be conducted to evaluate spatio-temporal evolution of these zones and their potential as predictors of future damaging landslides.