Gravity variations annually measurement (from 2000) with high precision interpreted together with the topographic deformations measured by GPS, San Juan, Argentina

FRANCISCO, RUIZ; NACIF, SILVINA; SISTERNA, JORGE; ACOSTA, GEMMA; NACIF, ANDRES; LEIVA, MARIA FLAVIA; FIGUEROA, MARA; CHRISIANSEN, R.

San Juan

Workshop; First International ANDES-GEO Workshop; 2018

Universidad Nacional de San Juan

Variations of gravity with higth precision has been controlled anually since 2000 with high precision (g4D) with eighty benchmarks ?Red G2?, around the city of San Juan, the sector between 31°S to 32°S latitude and 67,5°W to 69°W longitude was analyzed. Temporal gradients of g4D have been associated with active structures and interpreted as subsurface mass redistributions as a result of accumulation and release of stress. These data, in addition to topographic deformations measured by GPS and the identification of structures in thecrystalline basement from geophysical models, allow us to interpret mechanisms of deformation in the contact between the Precordillera and Pampean Ranges in the foreland of San Juan.In order to do so, we have materialized a GNSS geodetic network conformed by twenty gauge benchmarks, to detect seismo-tectonically induced temporal changes in its coordinates. The GNSS temporal network is complemented with four GNSS permanent stations. Four gradients from g4D, related to active structures surrounding San Juan city, have been detected in the study area. For example, after more than a decade with low activity, in 2012 the Tulum Fault System (TFS) was reactivated, generating crustal earthquakes of moderate magnitudeincluding an earthquake of Mw 5.0 (2012/01/18). According to our interpretation, the fault system accumulated elastic deformation for more than 10 years expressed as height increases at gravity stations (decrease of g4D) until the year 2011. The 2012/01/18 earthquake released part of the energy jointly with a co-seismic increase of g4D. This should be reflected in regional tectonic subsidence from the point of view of conventional gravimetric models. However, GPS reoccupation of the benchmarks located in this fault system, indicate a generalized altimetric ascent in the fault system in the last 15 years. TFS behavior could be assumed as topographic flexural displacements induced by a system of blinded faults. Deep structures in the cristalline basement affect the surface deformation generating blocks rotations.