Seismic faults analysis in California by means of the permanent scatterers technique

Spaceborne differential radar interferometry (14) has already proven its potential for mapping ground deformation phenomena in application to, among others, volcano dynamics (5), co-seismic (6-7) and post-seismic (8- 10) displacements of faults and slope instability (11). However, atmospheric disturbances (12-16) as well as phase decorrelation (17) have prevented hitherto this technique from achieving fall operational capability. These drawbacks are overcome by carrying out measurements on a subset of image pixels corresponding to natural or artificial stable reflectors (Permanent Scatterers, PS) and exploiting temporal series of interferometric data (18-19). Results obtained by processing 55 Synthetic Aperture Radar acquisitions of ERS satellites (European Space Agency) over Southern California, show that this approach allows one to push measurement accuracy very close to its theoretical limit of one millimetre. Though a full 3D displacement field cannot be recovered, the spatial density of measurements (up to 300 pS/km(2)), their accuracy and economic competitiveness, are far higher than corresponding values achievable with static GPS (20). PS time series analysis is therefore a powerful tool for risk assessment and is going to contribute significantly to improve our understanding of fault dynamics, stress accumulation and strain accommodation, evolution of soils, as well as systematic stability check of individual buildings and infrastructures.