In this paper we present the potential of a new compact superconducting gravimeter (GWR iGrav) designed for groundwater monitoring. At first, 3 yr of continuous gravity data are evaluated and the performance of the instrument is investigated. With repeated absolute gravity measurements using a Micro-g Lacoste FG5, the calibration factor (−894.8 nm s −2 V −1) and the long-term drift of this instrument (45 nm s −2 yr −1) are estimated for the first time with a high precision and found to be respectively constant and linear for this particular iGrav. The low noise level performance is found similar to those of previous superconducting gravimeters and leads to gravity residuals coherent with local hydrology. The iGrav is located in a fully instrumented hydrogeophysical observatory on the Durzon karstic basin (Larzac plateau, south of France). Rain gauges and a flux tower (evapo-transpiration measurements) are used to evaluate the groundwater mass balance at the local scale. Water mass balance demonstrates that the karst is only capacitive: all the rainwater is temporarily stored in the matrix and fast transfers to the spring through fractures are insignificant in this area. Moreover, the upper part of the karst around the observatory appears to be representative of slow transfer of the whole catchment. Indeed, slow transfer estimated on the site fully supports the low-flow discharge at the only spring which represents all groundwater outflows from the catchment. In the last part of the paper, reservoir models are used to characterize the water transfer and storage processes. Particular highlights are done on the advantages of continuous gravity data (compared to repeated campaigns) and on the importance of local accurate meteorological data to limit misinterpretation of the gravity observations. The results are complementary with previous studies at the basin scale and show a clear potential for continuous gravity time-series assimilation in hydrological simulations, even on heterogeneous karstic systems.

In November 2013 an International Key Comparison, CCM.G-K2, was organized in the Underground Laboratory for Geodynamics in Walferdange. The comparison has assembled 25 participants coming from 19 countries and four different continents. The comparison was divided into two parts: the key comparison that included 10 NMIs or DIs, and the pilot study including all participants. The global result given by the pilot study confirms that all instruments are absolutely coherent to each other. The results obtained for the key comparison confirm a good agreement between the NMI instruments. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

This study presents a compilation of more than 40 years of seismotectonic data, including 54 computed focal mechanisms, combined with 15 years of GPS data coming from a dense network of 35 permanent GPS stations within the Jura arc and its vicinity. These data are compared to previous available geomorphological, geophysical, and structural studies in order to discuss the 3D distribution of the deformation within the Jura arc. GPS data show coherent schemes in terms of velocities and allowed to discriminate between two provinces (NE of the belt and in its front/foreland). They also constrain a low but significant overall strain tensor with a NNW-SSE shortening of 2.16 nanostrain/year associated with an ENE-WSW extension of 0.44 nanostrain/year. The seismotectonic approach is based on a data set of 2,400 events and 54 focal mechanisms. Inversions of the focal mechanisms both globally and in homogeneous sectors highlight a general strike-slip deformation regime, with sigma1 oriented NW-SE and sigma3 oriented NE-SW. We discriminate two different sectors in terms of basement/cover (un)coupling: (1) potentially decoupled deformation between the basement and the sedimentary cover in the NE part; and (2) coupled deformation in the sedimentary cover and its basement in the Jura foreland.