Coseismic geodetic and geophysical variations detected for the January 19th, 2021 San Juan earthquake. Tectonic implications

Abstract

The coseismic surface variations and crustal deformation in the Central Precordillera region of San Juan(Argentina) as a consequence of the Mw 6.5 earthquake of January 19th, 2021 (2:46 UTC) were characterized bya multidisciplinary team, integrating information from Gravity, Seismology, GNSS and DInSAR (SyntheticAperture Radar Differential Interferometry) techniques.Prior to the occurrence of the event, several periodic measures were taken at fixed reference points throughoutSan Juan province. The results of the data analysis show significant changes in height corresponding to theuplifting of a few centimeters of the hanging wall block in accordance with the estimated deformation obtainedby the focal mechanism. In addition, the transcurrent component is evident in the GNSS vectors calculated afterthe earthquake. These results are consistent with the Gravity variations measured at the control points. Thisindicates the uplifting of the basement of Central Precordillera while the elastic Andean compressional deformation migrates N-E related to the Tulum lineament. The joint analysis of 4D gravity with GNSS heights showsan accumulation of deformation involving the lower crust prior to the earthquake, and the release of stresses withpermanent deformation, which partially complies with the laws of isostasy in the Precordillera, after theearthquake.