Surface deformation and secondary effects of the January 18, 2021 (Mw 6.5) San Juan (Argentina) earthquake from remote sensing techniques

Abstract

On January 18, 2021, a moderate earthquake (Mw 6.5) occurred ~ 45 km southwest of San Juan, a city in Central-Western Argentina, at a relatively shallow depth of ~ 20 km. The earthquake caused damage to the environment and infrastructure in the affected area, which is home to ~ 600,000 residents. To assess ground deformation, identify the seismogenic source, and evaluate the extent of secondary effects, we utilized Differential Synthetic Aperture Radar Interferometry (DInSAR) techniques in combination with Sentinel-2 visible and infrared imagery, as well as field data. DInSAR results suggested centimeter-scale ground deformation around the epicenter, off-fault deformation linked to regional structures, and site effects, such as liquefaction and landslides. By combining the values extracted from a 3-year-long PSI and SBAS time series, we estimated a vertical displacement of approximately 4.5 cm near the epicenter. Off-fault deformation involves some degree of ground settling on top of a blind or buried section of the Papagallos fault system, the reactivation of a section of the Rinconada fault system, and liquefaction and ground settling processes in the Tulum Valley. Rockfalls were distributed throughout a geologically diverse terrain and along a NW swath, with their occurrence controlled by the shaking intensity. The total area affected by secondary effects was ~ 3800 km2. Based on the available focal mechanism solutions and the distribution of environmental damage, we propose a left-lateral strike-slip displacement in a blind NW-striking fault, although different interpretations are discussed. Finally, we estimated the epicentral depth from SBAS time series Bayesian Inversion and from differential travel times pP-P, obtaining a depth of 20–25 km.