| Title | Towards the installation of a micro-seismic and a geodetic monitoring network for a geothermal project in urban context: the example of Illkirch-Graffenstaden (Alsace, France) |
|---|---|
| Authors | Maurer, V; Vergne, J; Richard, A; Doubre, C; Grunberg, M; Baujard, C; Wodling, H |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | Seismic and geodetic network installation, micro-seismic monitoring, site quality tests, geodetic monitoring, magnitude of completeness, Alsace |
| Abstract | A new deep geothermal project led by Electricity of Strasbourg is planned to exploit a fractured/faulted zone at about 2700 m deep in the southern part of the city of Strasbourg, in the town of Illkirch-Graffenstaden. This project, located in an urban area, will be framed by a ground motion monitoring network since acceptability issues raised. One the main concern of the surrounding population is the increase of micro-seismic activity and the eventual occurrence of structural damages on buildings due to surface deformation that may be induced by the geothermal activities. Therefore, a pluri-parametric geophysical network has been designed to detect various types of ground motions, from high-frequency micro-seismic events to slow displacements potentially characterized by low-frequency content signal, and from deep to surface deformation. This network will be composed of one strong-motion sensor, five short-period sensors and one broad-band sensor together with a geodetic station including one telemetered GNSS receiver and two corner reflectors for remote sensing survey of the surface displacements (radar interferometry). A specific methodology has been followed to select the future sites that will host the seismic permanent stations. First, the geometry of the seismic network has been chosen by minimizing the azimuthal gap for events located in the vicinity of the wells. Second, a series of tests has been conducted in order to estimate the noise level and eventually validate the site for a permanent installation. Third, in order to evaluate the magnitude of completeness of the future seismic network, an alternative approach is proposed based on the comparison of synthetic earthquakes and the level of noise recorded during the seismic noise tests. At 3 km depth, around the drilling platform, the estimated magnitude of completeness around the drilling site is about -0.5 considering a detection probability above 95% for at least 4 stations. |