Variaciones de gravedad en el Valle de Tulum, San Juan: aportes a la caracterización sismotectónica de la región
Keywords:
gravity changes, crustal movement, earthquakeAbstract
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.
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