ALBERT

Description: 〈span〉〈div〉SUMMARY〈/div〉Since the completion of the Gravity field and steady-state Ocean Circulation Explorer mission (GOCE), global gravity models of uniform quality and coverage are available. We investigate their potential of being useful tools for estimating the thermal structure of the continental lithosphere, through simulation and real-data test in Central-Eastern Europe across the Trans-European Suture Zone. Heat flow, measured near the Earth surface, is the result of the superposition of a complex set of contributions, one of them being the heat production occurring in the crust. The crust is enriched in radioactive elements respect to the underlying mantle and crustal thickness is an essential parameter in isolating the thermal contribution of the crust. Obtaining reliable estimates of crustal thickness through inversion of GOCE-derived gravity models has already proven feasible, especially when weak constraints from other observables are introduced. We test a way to integrate this in a geothermal framework, building a 3-D, steady state, solid Earth conductive heat transport model, from the lithosphere–asthenosphere boundary to the surface. This thermal model is coupled with a crust-mantle boundary depth resulting from inverse modelling, after correcting the gravity model for the effects of topography, far-field isostatic roots and sediments. We employ a mixed space- and spectral-domain based forward modelling strategy to ensure full spectral coherency between the limited spectral content of the gravity model and the reductions. Deviations from a direct crustal thickness to crustal heat production relationship are accommodated using a subsequent substitution scheme, constrained by surface heat flow measurements, where available. The result is a 3-D model of the lithosphere characterised in temperature, radiogenic heat and thermal conductivity. It provides added information respect to the lithospheric structure and sparse heat flow measurements alone, revealing a satisfactory coherence with the geological features in the area and their controlling effect on the conductive heat transport.〈/span〉

Description: 〈span〉〈div〉Summary〈/div〉Since the completion of the Gravity field and steady-state Ocean Circulation Explorer mission (GOCE), global gravity models of uniform quality and coverage are available. We investigate their potential of being useful tools for estimating the thermal structure of the continental lithosphere, through simulation and real-data test in Central-Eastern Europe across the Trans-European Suture Zone. Heat flow, measured near the Earth surface, is the result of the superposition of a complex set of contributions, one of them being the heat production occurring in the crust. The crust is enriched in radioactive elements respect to the underlying mantle and crustal thickness is an essential parameter in isolating the thermal contribution of the crust. Obtaining reliable estimates of crustal thickness through inversion of GOCE-derived gravity models has already proven feasible, especially when weak constraints from other observables are introduced. We test a way to integrate this in a geothermal framework, building a three dimensional, steady state, solid Earth conductive heat transport model, from the lithosphere-asthenosphere boundary to the surface. This thermal model is coupled with a crust-mantle boundary depth resulting from inverse modelling, after correcting the gravity model for the effects of topography, far-field isostatic roots and sediments. We employ a mixed space- and spectral-domain based forward modelling strategy to ensure full spectral coherency between the limited spectral content of the gravity model and the reductions. Deviations from a direct crustal thickness to crustal heat production relationship are accommodated using a subsequent substitution scheme, constrained by surface heat flow measurements, where available. The result is a three-dimensional model of the lithosphere characterised in temperature, radiogenic heat, and thermal conductivity. It provides added information respect to the lithospheric structure and sparse heat flow measurements alone, revealing a satisfactory coherence with the geologic features in the area and their controlling effect on the conductive heat transport.〈/span〉

Description: SUMMARY Since the completion of the Gravity field and steady-state Ocean Circulation Explorer mission (GOCE), global gravity models of uniform quality and coverage are available. We investigate their potential of being useful tools for estimating the thermal structure of the continental lithosphere, through simulation and real-data test in Central-Eastern Europe across the Trans-European Suture Zone. Heat flow, measured near the Earth surface, is the result of the superposition of a complex set of contributions, one of them being the heat production occurring in the crust. The crust is enriched in radioactive elements respect to the underlying mantle and crustal thickness is an essential parameter in isolating the thermal contribution of the crust. Obtaining reliable estimates of crustal thickness through inversion of GOCE-derived gravity models has already proven feasible, especially when weak constraints from other observables are introduced. We test a way to integrate this in a geothermal framework, building a 3-D, steady state, solid Earth conductive heat transport model, from the lithosphere–asthenosphere boundary to the surface. This thermal model is coupled with a crust-mantle boundary depth resulting from inverse modelling, after correcting the gravity model for the effects of topography, far-field isostatic roots and sediments. We employ a mixed space- and spectral-domain based forward modelling strategy to ensure full spectral coherency between the limited spectral content of the gravity model and the reductions. Deviations from a direct crustal thickness to crustal heat production relationship are accommodated using a subsequent substitution scheme, constrained by surface heat flow measurements, where available. The result is a 3-D model of the lithosphere characterised in temperature, radiogenic heat and thermal conductivity. It provides added information respect to the lithospheric structure and sparse heat flow measurements alone, revealing a satisfactory coherence with the geological features in the area and their controlling effect on the conductive heat transport.

Description: The Hunga Tonga Hunga Ha’apai (HTHH) islands have evolved since 2014, as we trace back through the SAR and multispectral satellite imaging of the Sentinels 1 and 2. The modulations of the outline of the islands are accompanied by mass changes, possibly detectable through a variation of the gravity field. These mass changes are the sum of the height changes of the emerging parts of the volcano, and the volume changes concealed below the ocean surface. The goal of the study is to define realistic mass changes that are associated to the evolution of HTHH, then to estimate the gravity changes in space and time, and finally estimate the sensitivity of observational methods to the gravity changes. Present ongoing efforts define the noise level in acquisitions of multi-satellite constellations carrying innovative instrumentation as quantum technology gravimeters or gradiometers [1,2]. The MAGIC mission planned for end of the 2020ties shall combine an inclined and polar pair of a GRACE-like mission to achieve a significant improvement in the recovery of the time variable gravity field. We find that the improvements of the future satellite missions should allow us to detect the subsurface mass changes generated by submarine volcanic activity, although the estimated mass changes for HTHH pose a challenge for the detectability. Next to HTHH we make a review of other known submarine eruptions and find that bigger volcanic mass changes are documented, which could be effectively observed. References[1] Migliaccio et al. (2023). SurvGeophys, https://doi.org/10.1007/s10712-022-09760-x[2] Pivetta et al. (2022). RemoteSensing, https://doi.org/10.3390/rs14174278

Description: Extensional tectonics in continental settings usually results in lithospheric stretching of narrow (e.g. Upper Rhine Graben), as well as wide regions (e.g. Basin and Range). Some rift systems bear evidence of a transition between the two styles: the West Antarctica Rift System (WARS) have likely progressed from diffuse to focused rifting (Cretaceous - Middle Neogene). The system currently covers a length of 1000 km, at the boundary between East and West Antarctica and is composed of four main basins (Victoria Land Basin, Central Trough, Northern Basin and Eastern Basin). The deformation pattern and available geological reconstructions suggest that, at least for some part of the rifting, the extension occurred concurrently in multiple sections.Inheritance of prior structural, thermal, and rheological heterogeneities is likely a controlling factor in this evolution [1]. Consequently, with the goal of identifying the most likely initial conditions, we designed a series of 2-D numerical models, analysing the effect of variations in the temperature field, rheology, accumulated strain, distribution of extensional pulses on the basins’ geometry. To this aim, we used the open source Underworld2 [2] and BGR-02 and ACRUP2 profiles [3], as 2-D analogue of the WARS structures in the Southern Ross Sea.The results show that the models most consistent with the observations are those that include inherited weakness zones at the cratonic boundary. Early onset of focused extension often occurs, with high sensitivity to the pattern of inherited weakening.[1] Perron et al. (2021). DOI:10.1051/bsgf/2020038[2] Mansour et al. (2020). DOI:10.21105/joss.01797[3] Trey et al. (1999). DOI:10.1016/S0040-1951(98)00155-3

Description: New mission concepts, such as the Mass change And Geosciences International Constellation (MAGIC), and advancements in instrumentation, such as quantum gradiometry, are expected to enhance the spatial and temporal resolution of gravity field observations. Simulations of these new constellations of instruments describe radical improvements in the error budget with respect to the signals arising from geophysical phenomena, including earthquakes. We assess the impact of these improvements in terms of earthquake detectability. In order to do so, we model an ensemble of synthetic earthquake gravity signals, using QSSPSTATIC [1], in terms of the spherical harmonics (SH) coefficients of the geopotential change due to an earthquake, as co-seismic signal of a dislocation and its variation in time due to viscoelastic relaxation. We test detectability with SH-domain SNR between the earthquake signal and the gravity model errors. The SH coefficients of both quantities undergo a spatio-spectral localization procedure [2] and are compared in terms of their localized degree variances. We perform a parametric study of the effect on detectability of moment magnitude and source parameters. Magnitude is a first-order predictor of detectability, while the effect of the other parameters is generally one order of magnitude smaller. We also assess the omission due to the point-source approximation, which we compare to finite fault solutions of real events. The results show that at the involved spatial scales and magnitudes, the point source approximation does not influence detectability significantly. [1] Wang et al., 2017 DOI:10.1093/gji/ggx259 [2] Wieczorek and Simons, 2005 DOI:10.1111/j.1365-246X.2005.02687.x

Description: Subduction of the Neotethys Ocean resulted in collisions of continental plates, with formation of Cenozoic orogens. The different shapes and structures of various segments of these young orogens, such the Zagros Collisional Zone, suppose a complex interplay of shallow and deep structures, producing different degrees and styles of deformation. As part of the PRIN 2017 project, we analyze several types of recently acquired data (e.g., seismic tomography models of the crust and upper mantle, Moho depth, seismicity distribution, and surface topography). We find that the NW and central Zagros is characterized by a zone of thickened crust of variable width and overlain by topography that exhibits large height variations over small distances, in the central part of the collisional zone. These variations are accompanied by sharp lateral changes in the number of seismic events and velocities/temperatures at depths of ~100 km. We attribute these observations to relamination processes (i.e., the detachment of Arabian crust from the subducting lithospheric mantle and its underthrusting beneath the crust of the overriding plate), which are controlled by the variable geometry and stiffness of the overriding and subducting plates. This hypothesis is tested by performing a series of numerical experiments, using the numerical code I2VIS [1], that simulates relamination processes, occurring during continental collision. The consistency of the results is also verified through forward models of the static gravity field of the modelled structures, which are compared with the present-day observed gravity. References [1] Gerya, T.V., 2019. Cambridge University Press. ISBN 978-0-521-88754-0.

Description: he joint ESA/NASA Mass-change And Geosciences International Constellation (MAGIC) mission has the objective to extend time series from previous gravity missions, including an improvement of accuracy and spatio-temporal resolution. The long-term monitoring of Earth's gravity field carries information on mass-change induced by water cycle, climate change, and mass transport processes between atmosphere, cryosphere, oceans and solid Earth. The MAGIC mission will be composed of two satellite pairs flying in different orbit planes. The NASA/DLR--led first pair (P1) is expected to be in a near-polar orbit around 500 km of altitude; while the second ESA--led pair (P2) is expected to be in an inclined orbit of 65--70 degrees at approximately 400 km altitude. The ESA--led pair P2 Next Generation Gravity Mission (NGGM) shall be launched after P1 in a staggered manner to form the MAGIC constellation. The addition of an inclined pair shall lead to reduction of temporal aliasing effects and consequently of reliance on de-aliasing models and post-processing. The main novelty of the MAGIC constellation is the delivery of mass-change products at higher spatial resolution, temporal (i.e. sub--weekly) resolution, shorter latency, and higher accuracy than GRACE and GRACE-FO. This will pave the way to new science applications and operational services. The performances of different MAGIC mission scenarios for different application areas in the field of geosciences were analysed in the frame of the initial ESA Science Support activities for MAGIC. The data sets provided here are the Level-2a simulated gravity field solutions of MAGIC scenarios and the related reference signal that were used for these analyses. The .gfc files in the folders monthly (31-day solutions) and weekly (7-day solutions) contain the estimated (HIS) coefficients (Cnm, Snm) as well as the formal errors (SigCnm, SigSnm) of the different MAGIC scenarios. In order to compute the coefficient errors, the reference/true HIS coefficients contained in the folder HIS_reference_fields need to be subtracted from the estimated HIS coefficients. The data sets provided here comprise the Level-2a simulated gravity field solutions of MAGIC scenarios and the related reference signal (based on Dobslaw et al. 2014; 2015) that were used for the above analyses.

Description: The joint ESA/NASA Mass-change And Geosciences International Constellation (MAGIC) has the objective to extend time-series from previous gravity missions, including an improvement of accuracy and spatio-temporal resolution. The long-term monitoring of Earth’s gravity field carries information on mass change induced by water cycle, climate change and mass transport processes between atmosphere, cryosphere, oceans and solid Earth. MAGIC will be composed of two satellite pairs flying in different orbit planes. The NASA/DLR-led first pair (P1) is expected to be in a near-polar orbit around 500 km of altitude; while the second ESA-led pair (P2) is expected to be in an inclined orbit of 65°–70° at approximately 400 km altitude. The ESA-led pair P2 Next Generation Gravity Mission shall be launched after P1 in a staggered manner to form the MAGIC constellation. The addition of an inclined pair shall lead to reduction of temporal aliasing effects and consequently of reliance on de-aliasing models and post-processing. The main novelty of the MAGIC constellation is the delivery of mass-change products at higher spatial resolution, temporal (i.e. subweekly) resolution, shorter latency and higher accuracy than the Gravity Recovery and Climate Experiment (GRACE) and Gravity Recovery and Climate Experiment Follow-On (GRACE-FO). This will pave the way to new science applications and operational services. In this paper, an overview of various fields of science and service applications for hydrology, cryosphere, oceanography, solid Earth, climate change and geodesy is provided. These thematic fields and newly enabled applications and services were analysed in the frame of the initial ESA Science Support activities for MAGIC. The analyses of MAGIC scenarios for different application areas in the field of geosciences confirmed that the double-pair configuration will significantly enlarge the number of observable mass-change phenomena by resolving smaller spatial scales with an uncertainty that satisfies evolved user requirements expressed by international bodies such as IUGG. The required uncertainty levels of dedicated thematic fields met by MAGIC unfiltered Level-2 products will benefit hydrological applications by recovering more than 90 per cent of the major river basins worldwide at 260 km spatial resolution, cryosphere applications by enabling mass change signal separation in the interior of Greenland from those in the coastal zones and by resolving small-scale mass variability in challenging regions such as the Antarctic Peninsula, oceanography applications by monitoring meridional overturning circulation changes on timescales of years and decades, climate applications by detecting amplitude and phase changes of Terrestrial Water Storage after 30 yr in 64 and 56 per cent of the global land areas and solid Earth applications by lowering the Earthquake detection threshold from magnitude 8.8 to magnitude 7.4 with spatial resolution increased to 333 km.