Joint inversion of co-seismic and early post-seismic slip: Application to the 2009 Mw6.3 LAquila earthquake, Central Italy

Théa Ragon , Anthony Sladen, Quentin Bletery, Mathilde Vergnolle, Olivier Cavalié, Antonio Avallone

Geodetic data provide static information on the displacement of the surface of the Earth, and allow for a detailed analysis of earthquake characteristics. Yet, geodetic data are generally characterized by either a good temporal or a good spatial resolution, but rarely both. This lack of resolution affects our understanding of the evolution of seismic and aseismic processes. Here, we propose a simple approach to counterbalance this lack of resolution by solving simultaneously for slip distributions on several time windows using datasets covering various time periods. This approach, also validated with a toy model, allows us to investigate the strictly co-seismic rupture of the Mw6.3 LAquila earthquake, Central Italy, and the processes at play on the fault during the first few days after the mainshock. We provide a strictly co-seismic slip model and a very early post-seismic model of the L’Aquila earthquake, and discuss the interactions between co-seismic slip, afterslip and aftershocks at short (6 days after mainshock) and long term (months after mainshock). We show that if the early post-seismic deformation is not acknowledged in earthquake source inversions, inferred co-seismic and post-seismic models may be largely biased. This work illustrates the importance of acknowledging the early post-seismic deformation to reliably address central scientific questions, such as the relationship between seismic and aseismic slip and their driving mechanisms, the interactions between on-fault deformation and aftershocks, and the agreement between nature and laboratory derived theories such as rate and state friction laws.