Matter-wave laser Interferometric Gravitation Antenna (MIGA): New perspectives for fundamental physics and geosciences

The MIGA project aims at demonstrating precision measurements of gravity with cold atom sensors in a large scale instrument and at studying the associated applications in geosciences and fundamental physics. The first stage of the project (2013-2018) will consist in building a 300-meter long optical cavity to interrogate atom interferometers and will be based at the low noise underground laboratory LSBB in Rustrel, France. The second stage of the project (2018-2023) will be dedicated to science runs and data analyses in order to probe the spatio-temporal structure of the local gravity field of the LSBB region, a site of high hydrological interest. MIGA will also assess future potential applications of atom interferometry to gravitational wave detection in the frequency band $\sim 0.1-10$ Hz hardly covered by future long baseline optical interferometers. This paper presents the main objectives of the project, the status of the construction of the instrument and the motivation for the applications of MIGA in geosciences. Important results on new atom interferometry techniques developed at SYRTE in the context of MIGA and paving the way to precision gravity measurements are also reported.Comment: Proceedings of the 50th Rencontres de Moriond "100 years after GR", La Thuile (Italy), 21-28 March 2015 - 10 pages, 5 figures, 23 references version2: added references, corrected typo

Spatial and Temporal Hydrodynamic Variations of Flow in the Karst Vadose Zone (Rustrel, France) in Function of Depth and Fracturing Density

International audienc

Imaging the lsbb environment from GPR data, along the tunnel and from the surface

ACTInternational audienc

Improving a 3D geological model using multiple geophysical methods

International audienc

Improving a 3D geological model using multiple geophysical methods

International audienceDue to strong lateral and vertical heterogeneities, enhanced characterization of the karst Unsaturated Zone (UZ) is a challenging task. Many geological, geotechnical and geophysical techniques allow collecting varied underground data on different spatial and temporal scales. However, coupled interpretation of these data remains difficult as the number of techniques increases and the interdependence of the measured properties is not straightforward. 3D modeling provides a framework for the global interpretation of the data. We propose a structural workflow mainly base on geophysical information to build the geological model of the karst UZ. Geological map, geotechnical cross-section and field observations described regional geological structures. Locally, Electric Resistivity Tomography (ERT), Ground Penetration Radar (GPR), and seismic surveys are used to refine the geological structures in a fine scale. The lithological interfaces, faults and fractures network are specified with metric resolution. This local geomodel will be used to constraint dimensions and discontinuities of a hydrogeological model for water flow simulations

Simultaneous geomagnetic monitoring with multiple SQUIDs and fluxgate sensors across underground laboratories

For two periods of several weeks duration in spring and autumn 2014, we monitored fluctuations in the geomagnetic field using 3-axis SQUID magnetometers at three locations within the LSBB tunnel network. Measurements at the water flow point C, and the GAS gallery supplemented the measurements by the permanent [SQUID]2 system in the Capsule. The frequency spectra of the magnetic fluctuations varied considerably between the three locations. These measurements have provided a unique data set to investigate the potential of underground SQUIDs to monitor the gradient of geomagnetic signals and thus investigate magnetotelluric effects and possible seasonal effects due to changes in the water content of the surrounding rock. We also compared the measurements of a SQUID and fluxgate system, and report on fluxgate measurements at the Boulby Underground Laboratory

Hydrodynamic organisation of the flows in the unsaturated zone of the Fontaine de Vaucluse karst system. First results

Karst systems contain important groundwater resources. Due to their complexity, they are generally under exploited. Particularly, the hydrodynamic functioning of the unsaturated zone is badly understood even if its important role is admitted Today, the hydrogeologists are agreeing with the important function(s) of the unsaturated zone in karst systems, but today this role(s) is badly characterized. As they are very complex systems, karst aquifers are generally under exploited. It is necessary to progress in the understanding of the functioning of the karst systems and particulary in the functioning of the unsaturated zone in order to develop the corresponding management tools. The study of the unsaturated zone of a karst system needs some access to this part of the aquifer. Speleological access is not sufficient because the major part of the water flows in not humanly enterable drains. The Low-Noise Underground Laboratory of Rustrel- Pays d’Apt (LSBB) is an artificial gallery digged in the unsaturated zone of the Fontaine de Vaucluse karst aquifer catchment area. It intersects arbitrarily the fault networks in depth and then the potential areas of flows through the unsaturated zone. From 2002 to 2009, 61 points where water regularly flows have been identified. For each, flow rate has been periodically monitored. This first global study of the acquired data shows a good relation between flows and geological structures. An organization of flows with depth and geology is also underlined. With increasing depth, flows seem to concentrate from numerous faults networks to a little number of high discontinuities

Groundwater dynamics in karst hydrosystem unsaturated zone; evidences from a 2-years Surface Nuclear Magnetic Resonance monitoring

International audienceThe unsaturated zone (UZ) of karst aquifers plays an important role in groundwater recharge processes. Comprehensive knowledge of UZ structure and hydrodynamic functioning is a key to better assess and manage groundwater resources in karst. In this extended abstract we present the results from a 2-year long Surface Nuclear Magnetic Resonance (SNMR) monitoring implemented in the Low-Noise Underground Laboratory (LSBB) site located within the Fontaine de Vaucluse karst hydrosystem in south-France. This exceptional 2-years SNMR monitoring demonstrated the efficiency of SNMR firstly to assess and validate the permanent presence of groundwater within karst hydrosystem UZ and secondly to monitor his temporal variations. Compared to boreholes, SNMR provides an integrated but accurate estimation of groundwater dynamics without disturbing the media

Geophysical investigations at the LSBB

ACTInternational audienc

Karst flow processes explored through analysis of long-term unsaturated-zone discharge hydrochemistry : a 10-year study in Rustrel, France

The unsaturated zone of karst aquifers influences the dynamics and the chemistry of water. Because of a lack of direct access, other than via caves, flows in the aquifer matrix and the smallest conduits remain poorly characterized. The few artificial underground structures in the unsaturated karst provide a rare opportunity to study the variety of flow processes. At the low noise underground research laboratory (Laboratoire Souterrain a Bas Bruit, LSBB) in Rustrel (France), 12 variables (temperature, pH, electrical conductivity, alkalinity, major anions and cations, total organic carbon) have been monitored on 12 perennial or temporary flows and leakages over a 10-year period covering contrasting climatic periods. This unique dataset of 1,135 samples has been used to discriminate, identify, and rank the processes associated with the hydrochemical variability of these different types of flows. A principal component analysis and a hierarchical cluster analysis, using mean values and standard deviation of the flow along the principal components, were performed. The results indicate that seasonal variability, mean water residence time, and the depth of acquisition of the chemical characteristics are the main factors of the variability of chemistry at the monitored flow points. Distinguished clusters highlight the great diversity of flows and processes occurring in the fine pathways that may be neighboring the large and structured fractures and conduits. Long-term monitoring with various climatic conditions appears to be a useful tool for assessing this diversity