InSAR measurement of crustal deformation transients during the earthquake preparation processes: a review

Crustal deformation is one of the most important parameters used for the observation and modelling of the seismic cycle of strain accumulation and release. The improvements of satellite Earth observation data and methods over the last two decades, have provided a way to measure crustal movements with good accuracy and spatial coverage. In particular, multi-temporal Synthetic Aperture Radar (SAR) satellite data sets and SAR interferometric techniques have demonstrated the capacity to obtain information on the dynamics of the deformation occurring during the various phases of the seismic cycle. In the last few years a number of papers have reported the occurrence of crustal deformation transients in the inter-seismic and post-seismic periods, and have speculated on their significance in the earthquake preparation processes. The foreseen steady flow of high quality SAR data provided by new satellites as Sentinel-1 and ALOS-2 is going to provide new pieces of evidence of these elusive phenomena, stimulating further observational and analytical research. In this paper we review data, methods and applications, to give the reader a view of the advantages and the limits of InSAR measurements for the investigation of transient surface deformation patterns.