| 1. |
- Mouyen, Maxime, 1982, et al.
(författare)
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Expected temporal absolute gravity change across the Taiwanese Orogen, a modeling approach
- 2009
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Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707. ; 48:3-5
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Tidskriftsartikel (refereegranskat)abstract
- The island of Taiwan is located on the convergent boundary between the Philippine Sea plate and the Chinese continental margin. It offers very active mountain building and collapsing processes well illustrated by the rugged topography, rapid uplift and denudation, young tectonic landforms, active faulting and numerous earthquakes. In this paper, using simple models, we have estimated vertical movements and associated absolute gravity variations which can be expected along a profile crossing the southern part of the island and probably suffering the highest rates of rising. The two different tectonic styles proposed for the island, thin-skinned and thick-skinned, were taken into account. Horizontal and vertical movements were modeled by an elastic deformation code. Gravity variations due to these deformations are then modeled at a second step. They are dominated by plate and free-air effects, i.e. elevation of the topography, with several μGal yr-1. By comparison, gravity changes generated by mass transfers are weak: maximum 0.1 μGal yr-1 with the thin-skinned tectonic and 0.3 μGal yr-1 with the thick-skinned tectonic. Though elastic rheology has limitations, this modeling offers interesting results on what gravity signal can be expected from the AGTO project (Absolute Gravity in the Taiwanese Orogen), which proposes to study the dynamic of these mountain ranges using absolute gravimetry (AG) and also including relative gravimetry (RG) and GPS measurements.
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| 2. |
- Kumar, Sandeep, et al.
(författare)
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Delineation of Aquifer Boundary by Two Vertical Superconducting Gravimeters in a Karst Hydrosystem, France
- 2023
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Ingår i: Pure and Applied Geophysics. - : Springer Science and Business Media LLC. - 0033-4553 .- 1420-9136. ; 180:2, s. 611-628
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Tidskriftsartikel (refereegranskat)abstract
- Mass distribution on Earth is continuously changing due to various physical processes beneath the Earth's surface or on the surface. Some of the primary sources for these mass displacements are tidal forces, atmospheric and oceanic loading, and seasonal changes in continental water distribution. The development of relative cryogenic gravimeters, the Superconducting Gravimeters (SGs), has made it possible to characterize and monitor such mass variations at orders of magnitudes as small as a few nm/s2 (1 nm/s2–10–10 g where g is the mean gravity at the Earth’s surface). Our study focuses on the hydrodynamics of the 900 m thick unsaturated zone of the low-noise underground research laboratory (Laboratoire Souterrain à Bas Bruit, LSBB) located in Rustrel (France) using a unique configuration of two SGs vertically arranged 520 m depth apart. The installation of an SG (iGrav31) at the site surface several years after installing the first (iOSG24) inside a tunnel has provided several new insights into the understanding of the hydrological processes occurring in the LSBB. By comparing differential and residual gravity time-series together with global hydrological loading models, we find that most water-storage changes occur in the unsaturated zone between both SGs. The misfit between the observed gravity time-series and the gravity effect corresponding to local hydrological contribution calculated from global hydrological models can be explained by large lateral fluxes and rapid runoff occurring in the LSBB site. Finally, we implement a rectangular prism method to compute forward gravity responses to water storage changes for a homogeneous water-layer following the site topography using a 5-m digital elevation model. In particular, we analyse the sensitivity of the differential record from both SGs to the extent and depth of the water storage changes by computing the corresponding 2D admittances. This gravity difference is sensitive to an extension up to about 2500 m laterally before tending towards an asymptotic value corresponding to the Bouguer plate approximation. We show that the zone of water-storage changes that best fits observed differential gravity signal is located at depths larger than 500 m (below iOSG24). This fitting is improving when the integration radius increases with depth. This is the first time that hydrological processes are investigated when the baseline configuration of two SGs is vertical.
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| 3. |
- Kumar, Sandeep, et al.
(författare)
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Groundwater monitoring and characterization by a vertical dipole of superconducting gravimeters in a karst aquifer, France
- 2021
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Ingår i: SEG Technical Program Expanded Abstracts. - : Society of Exploration Geophysicists. - 1052-3812 .- 1949-4645. ; 2021-September, s. 889-893
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Konferensbidrag (refereegranskat)abstract
- The Earth's mass distribution is continuously changing due to physical processes taking place either beneath the subsurface or on the surface. Some of the primary sources for these mass variations are tides in the ocean and solid Earth, atmospheric disturbances and seasonal climate changes. The development of Superconducting Gravimeters (SGs) has made it possible to characterize and monitor such mass variations at micro scales. Our study focuses on the LSBB karst catchment's hydrodynamics using a unique configuration of two SGs located 520 m depth apart. The installation of a SG (iGrav-31) at the surface of the LSBB several years after the installation of the first (iOSG-24) inside the tunnel has provided several new insights into the understanding of hydrological processes occurring in the LSBB. In this work, we compare differential and residual gravity time-series together with the ERA5 global hydrological loading model. In the subsequent section, we implement a rectangular prism method to compute forward gravity responses using input from the hydrological model. We also numerically evaluate and validate the already published hypotheses (Mouyen et al., 2019) about uncertainties related to groundwater storage's location in this catchment. Based on our observations, we find that most water-storage changes occur in the unsaturated karst zone between both SGs. The misfit between the residual gravity time-series and the local hydro-gravity effect computed from ERA5 model shows large lateral fluxes and rapid runoff occurring in the LSBB. Finally, we conclude this work by examining the radial and depth sensitivity of water masses' effect near the SGs, and enlisting some recommendations for further studies.
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| 4. |
- Mouyen, Maxime, 1982, et al.
(författare)
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Monitoring of groundwater redistribution in a karst aquifer using a superconducting gravimeter
- 2019
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Ingår i: E3S Web of Conferences. - : EDP Sciences. - 2555-0403 .- 2267-1242. ; 88
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Konferensbidrag (refereegranskat)abstract
- Geodetic tools monitor the earth's deformation and gravity field. They are presently sensitive enough to record subtle changes triggered by hydrological processes, thus providing complementary data to standard hydrological measurements. Among these tools, superconducting gravimeter (SG) have proven useful to unravel groundwater redistribution, which significantly alter the gravity field. In the frame of the EquipEx MIGA (Matter wave-laser based Interferometer Gravitation Antenna) project, one SG (iOSG-24) was set up in July 2015 in the Low-noise Underground Laboratory (LSBB) at Rustrel, France, in a gallery located 500 m beneath the surface. In this work, we analyse the underground iOSG-24 gravity time series together with hydro-meteorological data and basic gravity modelling. We find that the gravimeter recorded the redistribution of water in the ground and that most of this redistribution occurs in the unsaturated zone located above the gravimeter. Nevertheless, residuals between our model and the gravity data suggest the occurrence of large lateral fluxes and rapid runoff not considered in our model. We discuss how the setting of a second SG, planned in July 2018, at the surface of the LSBB could help unravelling such hydrological processes.
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| 5. |
- Pfeffer, Julia, et al.
(författare)
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Evaluating surface and subsurface water storage variations at small time and space scales from relative gravity measurements in semiarid Niger
- 2013
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Ingår i: Water Resources Research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 49:6, s. 3276-3291
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Tidskriftsartikel (refereegranskat)abstract
- The acquisition of reliable data sets representative of hydrological regimes and their variations is a critical concern for water resource assessment. For the subsurface, traditional approaches based on probe measurements, core analysis, and well data can be laborious, expensive, and highly intrusive, while only yielding sparse data sets. For this study, an innovative field survey, merging relative microgravimetry, magnetic resonance soundings, and hydrological measurements, was conducted to evaluate both surface and subsurface water storage variations in a semiarid Sahelian area. The instrumental setup was implemented in the lower part of a typical hillslope feeding to a temporary pond. Weekly measurements were carried out using relative spring gravimeters during 3 months of the rainy season in 2009 over a 350 × 500 m2 network of 12 microgravity stations. Gravity variations of small to medium amplitude (≤220 nm s-2) were measured with accuracies better than 50 nm s-2, revealing significant variations of the water storage at small time (from 1 week up to 3 months) and space (from a couple of meters up to a few hundred meters) scales. Consistent spatial organization of the water storage variations were detected, suggesting high infiltration at the outlet of a small gully. The comparison with hydrological measurements and magnetic resonance soundings involved that most of the microgravity variations came from the heterogeneity in the vadose zone. The results highlight the potential of time lapse microgravity surveys for detecting intraseasonal water storage variations and providing rich space-time data sets for process investigation or hydrological model calibration/ evaluation.
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