Zemmouri (Algeria) post-seismic surface deformation from Multi-Temporal InSAR analysis: after slip followed by visco-elasto-plastic relaxation mechanisms

Understanding deformation mechanisms throughout the seismic cycle—especially the modeling of post-seismic deformation, remains a challenging and actively debated topic. Analyzing the seismic loading process is essential as it provides critical information for improving earthquake hazard assessments. Strong earthquakes systematically induce crustal deformation at the surface, with effects lasting from weeks to decades and extending over large areas. Radar sensors onboard Earth observation satellites are widely used to measure ground deformation. In recent years, Multi-Temporal InSAR (MTI) methods have emerged as powerful tools for monitoring surface deformation over large areas. However, MTI-derived results are often affected by technical limitations and error sources. To obtain more reliable results and reduce errors, we have recently developed a new MTI method called Logarithmic Small Baseline Subsets (Log-SBAS). In this study, we apply the Log-SBAS method to detect and characterize post-seismic deformation induced by the 2003 May 21st, M _W 6.8 Zemmouri (Algeria) earthquake over 7 years-time-span. We then conducted a comprehensive assessment of the Log-SBAS method and compared it to the SBAS (Small Baseline Subsets) conventional MTI method. Our findings lead us to propose an alternative post-seismic deformation model to those proposed by other studies, suggesting an elastoplastic relaxation mechanism for the post-seismic phase. This mechanism is inferred from the spatio-temporal evolution of post-seismic deformation and the aftershocks sequence of the studied earthquake.