Work on the future seismological station OGCY began on 31 August 2020 in a rather special context. Indeed, the site is located at an altitude of 2200 metres, next to the Vanoise National Park, on the place called “Le Tougne”, in the middle of pastures. Despite the difficulties of access, a truck from the Technical Department of the CNRS-INSU, equipped for field missions (and carrying a compressor necessary for drilling), was able to access the site after a number of incidents (notably a mud slide). The work was completed without damage on 11 September 2020.
In Champagny-en-Vanoise, the ground is located on a moraine (a pile of eroded rock debris carried by a glacier that has disappeared since the last ice age), and is therefore not very conducive to a surface installation. The choice was therefore made to install the sensor in a borehole. The site is drilled to a depth of 6 metres, which is the standard size of the steel pipes laid at the time of drilling and which cannot be retouched. However, it was only necessary to go down to 1.5 metres to find a healthy rock to install the collector [1].
For the moment, the site is not yet instrumented. Eventually, a Centaur digitizer and a Trilium 120s PH seismometer will be installed, as for the other Reactive Drilling sites. The station will be integrated into the Permanent Broadband Network (RLBP) once operational.
[1] Indeed, it is important to place the future sensor under the moraine in a “healthy” rock (the basement). This improves the signal-to-noise ratio of the earthquake recordings and reduces environmental noise from the surface, which can be amplified by the sediment or moraine layer.
Contact
Benjamin Vial, benjamin.vial[at]univ-grenoble-alpes.fr
Truck of the Technical Department of CNRS-INSU stuck in the mud on the site of the seismological station OGCY in Champagny-en-Vanoise (Savoie) © Luigi Ardito, BRGM. To know more about it.
Seismological station OGCY at Champagny-en-Vanoise (Savoie) © Luigi Ardito, BRGM. To know more about it.