Red Argentina de Gravedad Absoluta (RAGA)

En el año 2015, el Instituto Geográfico Nacional oficializó la Red Argentina de Gravedad Absoluta (RAGA) medida en el año 2014 por el mencionado instituto en conjunto con la Universidad de San Pablo, las Universidades Nacionales de La Plata, Rosario y San Juan, el IRD (Institut de Recherche pour le Développement) y el BGI (Bureau Gravimétrique International) de Francia con un total de 35 puntos de gravedad absoluta distribuidos a lo largo de todo el Territorio Nacional y uno en la República Oriental del Uruguay.Facultad de Ciencias Astronómicas y Geofísica

Red Argentina de Gravedad Absoluta (RAGA)

En el año 2015, el Instituto Geográfico Nacional oficializó la Red Argentina de Gravedad Absoluta (RAGA) medida en el año 2014 por el mencionado instituto en conjunto con la Universidad de San Pablo, las Universidades Nacionales de La Plata, Rosario y San Juan, el IRD (Institut de Recherche pour le Développement) y el BGI (Bureau Gravimétrique International) de Francia con un total de 35 puntos de gravedad absoluta distribuidos a lo largo de todo el Territorio Nacional y uno en la República Oriental del Uruguay.Facultad de Ciencias Astronómicas y Geofísica

Red Argentina de Gravedad Absoluta (RAGA)

En el año 2015, el Instituto Geográfico Nacional oficializó la Red Argentina de Gravedad Absoluta (RAGA) medida en el año 2014 por el mencionado instituto en conjunto con la Universidad de San Pablo, las Universidades Nacionales de La Plata, Rosario y San Juan, el IRD (Institut de Recherche pour le Développement) y el BGI (Bureau Gravimétrique International) de Francia con un total de 35 puntos de gravedad absoluta distribuidos a lo largo de todo el Territorio Nacional y uno en la República Oriental del Uruguay.Facultad de Ciencias Astronómicas y Geofísica

Asperities and barriers on the seismogenic zone in North Chile: state-of-the-art after the 2007 Mw 7.7 Tocopilla earthquake inferred by GPS and InSAR data

The Mw 7.7 2007 November 14 earthquake had an epicentre located close to the city of Tocopilla, at the southern end of a known seismic gap in North Chile. Through modelling of Global Positioning System (GPS) and radar interferometry (InSAR) data, we show that this event ruptured the deeper part of the seismogenic interface (30–50 km) and did not reach the surface. The earthquake initiated at the hypocentre and was arrested ~150 km south, beneath the Mejillones Peninsula, an area already identified as an important structural barrier between two segments of the Peru–Chile subduction zone. Our preferred models for the Tocopilla main shock show slip concentrated in two main asperities, consistent with previous inversions of seismological data. Slip appears to have propagated towards relatively shallow depths at its southern extremity, under the Mejillones Peninsula. Our analysis of post-seismic deformation suggests that small but still significant post-seismic slip occurred within the first 10 d after the main shock, and that it was mostly concentrated at the southern end of the rupture. The post-seismic deformation occurring in this period represents ~12–19 per cent of the coseismic deformation, of which ~30–55 per cent has been released aseismically. Post-seismic slip appears to concentrate within regions that exhibit low coseismic slip, suggesting that the afterslip distribution during the first month of the post-seismic interval complements the coseismic slip. The 2007 Tocopilla earthquake released only ~2.5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500-km-long North Chile seismic gap

Spectromètre hertzien différentiel à traitement numérique-statistique

We describe a new microwave spectrometer which automatically and accurately measures the difference in inverse quality factor and the difference in resonance frequency between two similar resonators (one of which is used as reference). The spectrometer includes a lineary swept FM generator and, for each of the two resonators, an analog circuit for the measurement of the maximum power transmission (at exact resonance) and the detection of the exact times where the power transmission is à known fraction (usually 3/4) of this maximum. These timing signals for the two resonators are fed into a digital logical circuit and time interval counter which averages the results over a large number of frequency sweeps and displays the averages. The spectrometer operates over a frequency range extending from 0.1 GHz to 100 GHz, its accuracy is of the order of 1 % on the differences of resonance frequency (differences of a few Hz can be detected) and of a few per cent on the differences of inverse quality factor. The instrument is directreading, stable, fiable and easy to use.Un spectromètre hertzien original est étudié et réalisé. Il est basé sur un principe différentiel (la réponse d'un résonateur de mesure est comparée à celle d'un résonateur semblable de référence) et fait appel au traitement numérique-statistique des signaux, la réalisation profitant des techniques électroniques actuelles. Ce spectromètre est caractérisé par une haute sensibilité (on peut distinguer quelques Hz sur une fréquence se situant dans le domaine de 0,1 à 100 GHz), une précision élevée (de l'ordre de 1 % sur les différences entre les fréquences de résonance des résonateurs, de quelques pour cent sur les différences entre les inverses des coefficients de qualité), une stabilité et une fiabilité bonnes, une utilisation facile (les résultats sont disponibles en chiffres visualisés, sur imprimante ou sur enregistreur). On aboutit à un instrument très efficace, qui peut être utilisé à de nombreuses recherches physiques et à diverses applications

The new Absolute Quantum Gravimeter (AQG): first results and perspectives

International audienc

Insight into ground deformations at Lascar Volcano (Chile) from SAR Interferometry, photogrammetry and GPS data: implications on volcano dynamics and future space monitoring

International audienceWe present a detailed study of Lascar volcano (Chile) based on the combination of satellite, aerial and ground-based data, in order (i) to better characterize the deformation style of Andean explosive volcanoes, and (ii) to provide new insights on the potential of space techniques to monitor active volcanic deformations on such edifices. Lascar is one of the most active volcanoes in Central Andes characterized by a recent cyclic activity. Additionally, it is located in favourable conditions for radar imaging. Lascar thus offers very good conditions for studying large to small scale ground deformations associated with volcano dynamics. The analysis of InSAR (Synthetic Aperture Radar interferometry) time series data from the European and Japanese satellites (ERS, JERS) acquired between 1993 and 2000, encompassing three eruptive events, confirmed the absence of broad far-field deformation signal. Thus during the recent activity of Lascar we discard significant magmatic input at depth. The following approaches were used to improve the InSAR signal/noise ratio in order to detect possible local deformation. We carried out a quantitative evaluation of the potential tropospheric contribution in INSAR interferograms for the Salar de Atacama-Lascar area using radar (ASAR-ENVISAT) and spectrometer (MODIS) data. We also used an accurate aerial photogrammetric and GPS constrained DEM in our InSAR data reprocessing. We find a co-eruptive ground-deformation confined into the summit crater for the 1995 eruption. This deformation has spatial dimension of 500 by 400 in and relates to a subsidence of crater floor up to 17 mm. We interpret it as pressure or volume decrease at subsurface levels below the active crater. Our study made it possible to image a new near-field volcanic deformation confined within the summit crater of the Lascar volcano. It also demonstrates that the combination of precise photogrammetry DEM and INSAR data can significantly improve our ability to remotely sense subtle surface deformation on these explosive volcanoes. This methodology might contribute to better understand volcano dynamics and to complement their monitoring in remote areas

The new Absolute Quantum Gravimeter (AQG): first results and perspectives

International audienc

The new Absolute Quantum Gravimeter (AQG): first results and perspectives

International audienc