Medición y cálculo de la Red Gravimétrica Nacional: RED ARGENTINA DE GRAVEDAD ABSOLUTA

La historia de la actividad gravimétrica en nuestro País está íntimamente vinculada al instituto Geográfico Nacional en tanto el mismo asume por Ley la responsabilidad de la instalación y mantenimiento de las Redes Geodésicas Nacionales (Ley 22963, 1983). No obstante ello, han sido numerosas las instituciones científicas y educativas que han participado desde el mismo inicio de las tareas en esta especialidad, colaborando con el Organismo, no sólo en su establecimiento sino también en la planificación de las redes, atento a las necesidades de la comunidad en general y la ciencia en particular. Los avances provenientes de la tecnología satelital y la explosión informática, fueron acompañados en el ámbito de la Geodesia por exigencias de precisión cada vez mayores. Si en su definición clásica, entendemos a la Geodesia como la ciencia que se ocupa de determinar la forma y dimensiones de la Tierra, deberíamos convenir que una definición moderna debería incluir la referencia a una determinación “precisa”. Alcanzar tales precisiones requiere de un Marco de Referencia acorde a la época actual, definido con instrumental y procedimientos que se ajusten a los estándares internacionales vigentes y en capacidad de dar respuesta a los cada vez más exigentes requerimientos de la ciencia y su aplicación práctica. La Red Gravimétrica Nacional de Orden Cero debe materializar ese Marco moderno y preciso, y será necesario que esa estructura de base sobre la cual secimientan las demás Redes, responda con solidez a las más altas exigencias de calidad. Lamentablemente nuestro País contaba al inicio del presente trabajo con apenas cinco puntos de gravedad absoluta medidos hace más de 30 años. La posibilidad de transformar esos puntos escasos y dispersos en una Red moderna, sólida y confiable constituyó la motivación fundamental del Proyecto sobre el cual se fundamenta esta Tesis Doctoral

Crustal motion in the zone of the 1960 Chile earthquake: Detangling earthquake-cycle deformation and forearc-sliver translation

Temporary deformation in great earthquake cycles and permanent shear deformation associated with oblique plate convergence both provide critical clues for understanding geodynamics and earthquake hazard at subduction zones. In the region affected by the Mw 9.5 great Chile earthquake of 1960, we have obtained GPS observations that provide information on both types of deformation. Our velocity solutions for the first time span the entire latitudinal range of the 1960 earthquake. The new observations revealed a pattern of opposing (roughly arc-normal) motion of coastal and inland sites, consistent with what was reported earlier for the northern part of this region. This finding supports the model of prolonged postseismic deformation as a result of viscoelastic stress relaxation in the mantle. The new observations also provide the first geodetic evidence for the dextral motion of an intravolcanic arc fault system and the consequent northward translation of a forearc sliver. The sliver motion can be modeled using a rate of 6.5 mm/a, accommodating about 75% of the margin-parallel component of Nazca-South America relative plate motion, with the rate diminishing to the north. Furthermore, the new GPS observations show a southward decrease in margin-normal velocities of the coastal area. We prefer explaining the southward decrease in terms of changes in the width or frictional properties of the megathrust seismogenic zone. Because of the much younger age of the subducting plate and warmer thermal regime in the south, the currently locked portion of the plate interface may be narrower. Using a three-dimensional viscoelastic finite element model of postseismic and interseismic deformation following the 1960 earthquake, we demonstrate that this explanation, although not unique, is consistent with the GPS observations to the first order. Copyright 2007 by the American Geophysical Union

Crustal motion in the Southern Andes (26°-36°S): Do the Andes behave like a microplate?

[1] A new Global Positioning System (GPS)-derived velocity field for the Andes mountains (26°-36°S) allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen\u27s opposing sides. Adding an \u27\u27Andes\u27\u27 microplate to the traditional description of Nazca-South America plate convergence provides the kinematic framework for nearly complete explanation of the observed velocity field. The results suggest the oceanic Nazca boundary is fully locked while the continental backarc boundary creeps continuously at ̃4.5 mm/yr. The excellent fit of model to data (1.7 mm/yr RMS velocity misfit), and the relative aseismicity of the upper crust in the interior Andean region in comparison with its boundaries, supports the notion that the mountains are not currently accruing significant permanent strains. Additionally, the model implies permanent deformation is not accumulating throughout the backarc contractional wedge, but rather that the deformation is accommodated only within a narrow deformational zone in the backarc

The Nazca-South America Euler vector and its rate of change

We present velocities relative to the South American plate for five GPS stations on the Nazca plate and use these measurements to estimate the modern Euler vector. We find a pole at 55.8°N, 92.5°W with a rotation rate of 0.60 °/Myr. Because the GPS station at Easter Island appears to be moving at approximately 6.6 mm/yr relative to the other Nazca stations, we repeat our analysis with this station excluded from the inversion to obtain a second and preferred result (called CAP10) with a pole at 61.0°N, 94.4°W and a rate of 0.57 °/Myr. We compare these results with published finite rotation vectors and infer that during the past 10-20 Myrs, the Nazca-South America rotation rate has decelerated by 0.04°-0.06 °/Myr2. © 2003 Elsevier Science Ltd. All rights reserved

The history, state, and future of the argentine continuous satellite monitoring network and its contributions to geodesy in Latin America

Since its creation in 1998, the Argentine Continuous Satellite Monitoring Network (Red Argentina de Monitoreo Satelital Continuo [RAMSAC]) has grown to include more than 100 continuously operating Global Navigation Satellite Systems (GNSS) stations in Argentina. RAMSAC Receiver Independent Exchange Format (RINEX) data and their derived positioning products (e.g., Networked Transport of RTCM via Internet Protocol [NTRIP] streams and time series) have been used in more than 20 peer-reviewed publications studying the inter-, co-, and postseismic geodynamic evolution of the subduction interface between the South America and Nazca plates. Most of this research has focused on the deformation associated with the near-field megathrust earthquake cycle. Nevertheless, many authors have begun to include in their analyses far-field GNSS observations, which in general do not follow the elastic/ viscoelastic deformation predicted by current models. We review the contribution of RAMSAC to scientific knowledge of earthquake elastic deformation and associated phenomena. We also describe the future plans for RAMSAC and the societal impact beyond geodetic and geophysical science

Crustal motion in the zone of the 1960 Chile earthquake: Detangling earthquake-cycle deformation and forearc-sliver translation

Temporary deformation in great earthquake cycles and permanent shear deformation associated with oblique plate convergence both provide critical clues for understanding geodynamics and earthquake hazard at subduction zones. In the region affected by the Mw 9.5 great Chile earthquake of 1960, we have obtained GPS observations that provide information on both types of deformation. Our velocity solutions for the first time span the entire latitudinal range of the 1960 earthquake. The new observations revealed a pattern of opposing (roughly arc-normal) motion of coastal and inland sites, consistent with what was reported earlier for the northern part of this region. This finding supports the model of prolonged postseismic deformation as a result of viscoelastic stress relaxation in the mantle. The new observations also provide the first geodetic evidence for the dextral motion of an intravolcanic arc fault system and the consequent northward translation of a forearc sliver. The sliver motion can be modeled using a rate of 6.5 mm/a, accommodating about 75% of the margin-parallel component of Nazca-South America relative plate motion, with the rate diminishing to the north. Furthermore, the new GPS observations show a southward decrease in margin-normal velocities of the coastal area. We prefer explaining the southward decrease in terms of changes in the width or frictional properties of the megathrust seismogenic zone. Because of the much younger age of the subducting plate and warmer thermal regime in the south, the currently locked portion of the plate interface may be narrower. Using a three-dimensional viscoelastic finite element model of postseismic and interseismic deformation following the 1960 earthquake, we demonstrate that this explanation, although not unique, is consistent with the GPS observations to the first order. Copyright 2007 by the American Geophysical Union