S046-0003
Evolution of the Concordia seismological observatory station CCD (GEOSCOPE network): a new post-hole installation on Antarctica inlandsis
Monday, 14 December 2020
Poster
Maxime Bès de Berc1,2, Dimitri Zigone1,2, Peter Danecek3, Alain Steyer1,2, Francesco Zanolin3, Olivier Alemany4, Philippe Possenti4, Jean-Yves Thore1,2, Hervé Blumentritt1,2, Adriano Cavaliere3, Nathalie Cotte5,6, Stefano Marino3, Alessia Maggi1,2, Armelle Bernard1,2, J-Jacques Leveque1,2, Martin Vallée7, Nicolas Leroy7, Eleonore Stutzmann8, Frédérick Pesqueira7 and Constanza Pardo7, (1)EOST École et Observatoire des Sciences de la Terre, Strasbourg Cedex, France, (2)Institut de Physique du Globe Strasbourg, Strasbourg Cedex, France, (3)Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy, (4)Centre National de la Recherche Scientifique, Institut de Géophysique de l'Environnement, Saint Martin d'Hères, France, (5)Université Grenoble Alpes, Saint Martin d'Heres, France, (6)ISTerre Institute of Earth Sciences, Saint Martin d'Hères, France, (7)Université de Paris, Institut de physique du globe de Paris, Paris, France, (8)Université de Paris, Institut de physique du globe de Paris, CNRS, Paris, France
Abstract:
Concordia (75°S 123°E) is a scientific base operated by French and Italian polar institutes, and is located at Dôme C, on the inlandsis of the East Antarctica plateau. It hosts a seismological station (CCD), which is a joint program between EOST (Strasbourg) and INGV (Roma). The Concordia seismological observatory, built in 2000 with state-of-the-art surface instrumentation installed in a vault made of snow-covered containers, meets the required quality criteria and has been part of the GEOSCOPE network since 2008. However, it has become necessary to replace this installation for safety reasons, recurring snow coverage issues and seismological performances. The existing seismic vault is deformed by the hydrostatic pressure of the snow. Its proximity to the base causes strong daytime noise (~30 dB) at high frequencies (>1 Hz); the unconsolidated layer of snow about 100m thick forms a waveguide that traps anthropogenic noise from the base. In addition, a coupling defect of the instruments in contact with the snow limits the performance at low frequencies (< 0.03 Hz) on the horizontal channels.
Six years ago, we proposed to install a borehole seismometer at a depth of 120m in order to limit the waveguide effects. A new shelter on stilt and the borehole drilling were carried out in the summer of 2018/2019. The installation of all the instrumentation has just been completed by our team in January 2020. The sensor was installed in a bed of fine sand, directly in the hard ice, allowing it to improve its coupling with the medium. The analyses of the data show that the high-frequency disturbances are very largely attenuated (-30 dB at 10 Hz) compared to the surface installation and that the horizontal channels have a lower noise level at low frequencies (-20 dB at 0.01Hz). In addition, data for all components are below the standard noise model for frequencies between 5 and 9Hz, which already makes this new station one of the quietest installations in the world for those frequencies. These measurements, already excellent in terms of seismological performance, will be monitored to ensure the stability of the installation and the good continuity of the data before being distributed by the GEOSCOPE network. This new type of installation, a precursor in Antarctica and extremely promising, is set to become a standard in Antarctic seismology.
