Resolving blind mid-crustal earthquake deformation with InSAR time-series: the 2021 <i>M</i> w 6.4 San Juan earthquake and implications for a non-optimal fault reactivation in the Andean Fold and Thrust Belt, Argentina

SUMMARY On 2021 January 18, a blind mid-crustal $M_w\, \sim$6.4 earthquake occurred near San Juan, Argentina. The observation of associated ground deformation with single interferograms is obscured by strong tropospheric signals. We apply appropriate corrections to the data and reconstruct the deformation field associated to the event through InSAR time-series approach. We show it is possible to retrieve this signal to invert the fault parameters. The observed ground deformation is consistent with a high angle NW-dipping fault plane at a centroid depth of $\sim$19 km. The geometry of this fault supports the reactivation of pre-existing structures within the Cuyania Terrane, suggesting a direct structural connection and strain transfer to the actively deforming, east-vergent Precordillera front. We analyse our findings to deduce a static friction coefficient $\le 0.3$ for mid-crustal faults of the region.