Abstract

RUIZ, Francisco; INTROCASO, Antonio; GALLEGO G., Álvaro  and  LAPLAGNE, Alfredo. Variaciones de gravedad en el Valle de Tulum, San Juan: aportes a la caracterización sismotectónica de la región. Geoacta [online]. 2008, vol.33, pp.104-109. ISSN 1852-7744.

A network of areal geodetic control (Red G1) was set up with the purpose of establishing space-time relations in the evolution of the gravity field produced by seismo-tectonic activity. The network is composite for points well materialized in the field, and extends over an about 2500 km² area centered in the San Juan city. These fixed points were linked with precise gravity measurements carried out during years 2000 and 2004. The gravity changes 2000-2004 are evaluated taking as fix the gravity value in the Instituto Geofísico Sismológico (UNSJ) station. The relative gravity variation field shows a consistent relation with the seismic activity with magnitudes higher than 3 in the area, which was frequent during these years. The most outstanding results indicate that: A) An alignment of maxima with variations up to +0.088 mGal occurs in the Southwest of the Pie de Palo range, of +0.045 mGal in the Barboza, and of 0.065 mGal in the Valdivia interior mountains. B) A zone with maxima up to +0.090 mGal was determined in the central-west sector of the Sierra Chica de Zonda range, correlated with seismic swarms with magnitudes 3 to 3.9. C) A marked quiescence in the fixed points situated to the South of the Sierra Chica de Zonda range. D) A generalized upward zone in the stations situated north of the San Juan River, up to +0.080 mGal in the La Laja fault, where the epicenter of the 15/01/1944 earthquake was located. If we assign the gravity variations as caused entirely by topographic changes, the height variations would be in the neighborhood of 10 cm.

Keywords : Gravity changes; Crustal movement; Earthquake.

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