Claudia Tocho

Analysis of the Discrepancies Between the Vertical Reference Frames of Argentina and Brazil

The vertical reference frames for Argentina and Brazil present discrepancies due to their different datums and realizations. Thus, since 2008, we have started a series of activities with the aim of unifying the Argentine and Brazilian national vertical networks (NVNs). To achieve this goal, we have connected the two NVNs at three border points by using the geodetic levelling approach. Additionally, the gravity field approach was also applied, based on a suitable representation of the geoid by considering the Earth Gravitational Model (EGM2008) in its full resolution. In this regard, 1266 co-located Global Positioning System (GPS) and levelling benchmarks regularly distributed over Argentina (612) and Brazil (654) were considered. The geodetic levelling approach shows an offset value of 54 cm, which implies that the Argentine vertical reference frame is above that of the Brazilian vertical reference frame. However, the result of the gravimetric approach shows an offset of 57 cm, which implies a difference of approximately 3 cm between both methods. Hence, since Brazil and Argentina represent a significant part of South America, the solution to the datum problem between both countries could point towards a common vertical reference frame for the Atlantic side.

A Preliminary Geoid Model for Argentina

Instituto de Fisica de Rosario (IFIR), Facultad de Ciencias Astronomicas y Geofisicas de La Plata (FCAGLP) in a cooperation with Escola Politecnica of the University of Sao Paulo are involved in an effort for the determination of the geoid in Argentina. For this purpose, softwares have been set up at FCAGLP in order to perform the main tasks for geoid computations: processing of gravity data to derive mean gravity anomalies, dealing with geopotential models, performing the numerical integration of the modified Stokes’s formula. The recent NASA/NIMA geopotential model, EGM96, is used as a reference field in the remove-restore technique. A preliminary model has been computed for Argentina with a resolution of 20’ × 20’. A total of 55 GPS points established on the geometric leveling network have been used for a comparison with the undulations derived from gravimetric information. The activities related to the geoid in Argentina are carried out under the umbrella of the Sub-Commission for the Geoid in South America (SCGSA).

First Six Months of Superconducting Gravimetry in Argentina

On December 16th, 2015, the superconducting gravimeter SG038 started to measure again after it was moved from the previous station in Concepcion, Chile to the Argentine-Germany Geodetic Observatory (AGGO) near the city of La Plata in Argentina.

Seasonal Variability of Land Water Storage in South America Using GRACE Data

The objective of the present study is to analyze seasonal variability of land water storage in South America from GRACE data. High precision estimate of temporal variations in the Earth’s gravity are obtained using monthly Release-04 (RL04) gravity field coefficients provided by the Center for Space Research (CSR) of the University of Texas at Austin. Water mass anomalies, as equivalent height of water, are calculated based on the direct relationship between gravity and mass. To remove the effects of the noise observed in the equivalent-water thickness solutions at high harmonic degrees, an optimized smoothing technique is applied. Finally, temporal distributions of land water storage are compared to monthly mean precipitation data extracted from in-situ rain gauge records in order to identify, correlate and understand patterns of water movement at continental scale in South America.

New Results in the Determination of the Geoid Model in Argentina

Improvements in the geoid model of Argentina have been developed by means of incorporating new data, testing an other software package and adding GPS/levelling information.

Esquema de tres interfaces con compensación isostática local en el margen continental Argentino

In the present paper, we investigate the Airy type isostatic compensation scheme for three interfaces: water-sediments, sediments-crust and crust-mantle, using forward modelling to calculate the isostatic anomaly with different approximations of Parker’s expression in the Argentine continental margin. The isostatic anomaly is estimated as the residue between the observed free air anomaly and the calculated free air anomaly through the sum of the contributions from the tree interfaces. After that, we perform the inversion of the isostatic anomaly in order to find the deflection of the Moho necessary to compensate it (or minimize it) using one term of Parker’s expression in the inversion, as an experiment to test the numerical methods. The Moho here considered is obtained from knowing the depth of the basement and crustal thickness. Another way to estimate the crust-mantle interface (Moho) is by the inversion with the iterative method of Parker-Oldenburg (Parker, 1973; Oldenburg, 1974), which allows inverting the Bouguer anomaly with more than one term. With the Moho thus obtained, a free-air gravity anomaly can be calculated, which reproduces the observed anomaly quite well. Even considering that the experiment constitutes a schematic model just to test the numerical methods involved, from the comparison with the only available digitized refraction profile in the study area, we find that the large wavelength of the inverted Moho is reproduced fairly well by the modeled Moho for both methods. However, the iterative method yields smoother surfaces, possibly more realistic surfaces given the roughness that the other estimates present.

Mohorovicic Discontinuity Depth Analysis Beneath North Patagonian Massif

The Mohorovicic discontinuity (Moho) is the surface that limits the Earth’s crust and mantle. It is of paramount importance in understanding and investigating the dynamics of the Earth’s interior. The GEMMA project (GOCE Exploitation for Moho Modeling and Applications), funded by the European Space Agency and Politecnico di Milano, has provided a high resolution map of the Moho surface (GEMMA Model), based on the inversion of homogeneous, well-distributed gravimetric data measured by the Steady-State Ocean Circulation Explorer (GOCE), which ensures a global coverage using gravity field. In the current paper, this Moho depth estimation (Riccardo Barzaghi, personal communication, April 20, 2012) is compared with other models based on both seismic and gravity observations, under the North Patagonian Massif (NPM). Said massif is an Argentinean plateau that stands out 500 to 700 m higher in altitude than the surrounding topography and was created by a sudden uplift without noticeable internal deformation (Aragon et al. (2011b) Upper mantle geodynamic constrains beneath the north patagonian massif, Argentina). The features described led us to analyze the crustal thickness in the area. The work describes different Moho models available in the area under study and their comparison with the GEMMA Model. The aim is to validate this well distributed, homogeneous data model in this area with sparse seismic data and check its usefulness to get more information about the Moho. According to comparisons with the different models, the crustal thickness in the study area varies between 36 and 46 km. The good agreement between the GEMMA Model and some of the other Moho models may account for the use of such model to study this little known area.