Designing a new post­hole seismological station on Antarctica inlandsis (Concordia station)

• Main Authors: Bes de Berc, Maxime, Maggi, Alessia, Leveque, Jean-Jacques, Thoré, Jean-Yves
• Other Authors: Institut de physique du globe de Strasbourg (IPGS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Ecole et Observatoire des Sciences de la Terre (EOST)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2015
• Subjects: [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; Concordia Station; East Antarctica; Antarc*; Antarctica; Antartide; Inlandsis
• Online Access: https://hal.science/hal-03198072; https://hal.science/hal-03198072/document; https://hal.science/hal-03198072/file/AGU2015-Ccd.pdf

International audience Concordia (75°S 123°E) is a scientific base operated by French and Italian polar institutes IPEV (Institut PaulEmile Victor) and PNRA (Programma Nazionale di Ricerche in Antartide, and is located on the inlandsis of the East Antarctica plateau. It hosts a seismological station CCD which has provided observatory quality data since the year 2000, has been integrated into the Geoscope network since 2008 and whose data are now available in realtime from IRIS. The current seismic vault is located 800m from Concordia base, as far away as is deemed logistically possible by IPEV, at a depth of 12m. The vault is thermally very stable, but given the close distance to the base, suffers from increased diurnal noise (up to 40 dB) at frequencies above 1Hz, especially in the summer season. Anthropic noise is trapped in the firn (snow) layer, which forms an 100110m thick waveguide, and is picked up very easily in the seismic vault. The vault is made from steel containers buried vertically in the snow. The hydrostatic pressure of the snow is deforming them: we see container cracking events on the seismograms, and also visual evidence of container deformation inside the vault. In the near future, this deformation will create a security problem. We have decided to progressively abandon our current vault, and construct a new posthole seismological installation nearby. We plan to drill to 130m depth, which would place us below the firn layer waveguide and also below the ice pinchout depth. To be able to run the station for several years and change or service the instrumentation if required, we need to keep the hole open, to avoid any hydrostatic movement, and to maintain good coupling between the sensor and the surrounding hard ice. To achieve these goals, we shall install a casing in the fin layer and then drill a few meters more without casing in hard ice. After installing the instrument, we shall then fill the whole hole with a drilling fluid whose density is similar to that of ice. The drilling will be ...