Resumen

RUIZ, Francisco et al. Gravity changes of tectonic origin in the transition between western Sierras Pampeanas and Precordillera of San Juan. Rev. Asoc. Geol. Argent. [online]. 2011, vol.68, n.4, pp.594-605. ISSN 0004-4822.

Earthquake is closely tied up with gravity changes on the basis of crustal deformation and crustal density changes. A network of areal geodetic control was set up with the purpose of establishing space-time relations in the evolution of the gravity field produced by tectonic activity. The network is composed by 65 bench marks well materialized in the field, and extends over an area of about 3,500 km2 centered in the San Juan city. Ten years of gravity periodic measurements have allowed to evaluate the speeds of the gravitational intensity field variations. These gravity changes adjust reasonably well with the statistical lineal regression model applied to the gravity versus time observations. The observed data support the current uplift of the Eastern Precordillera, reflected in increases of gravity (g) in all bench marks located westwards of the Villicum-Ullum-Zonda fault and in the decrease of gravity eastwards of this structure. We identify three segments of larger activity: a) La Laja fault with strong decreases of g, b) Maradona-Cerro Bayo segment, with increases of g westwards of the Sierra Chica de Zonda and c) decreases of g at La Rinconada fault. The data show tectonic activity in the Tulum faults system, gravity changes have lined up in the Cerro Valdivia-Cerro Barboza-Sierra de Pie de Palo lineament and increase to the east. The largest variations are observed eastwards of the Barboza hill with a minimum of g. Magnetic and gravity anomaly maps indicate basement patterns consistent with these active structures.

Palabras clave : 4D gravity monitoring; Crustal mobility; Seismogenic sources.

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