1,721,090 research outputs found
Tectonic and climate induced mass changes - competing signals in long term gravity signals
Full text linkSeveral mountain ranges as Alps, Himalaya and Tibet are presently subject to uplift, as documented by GNSSvertical movement rates. Uplift occurs in response to climatic mass loss (deglaciation or hydrologic mass loss)or due to the dynamic forces (crustal compression or mantle inflow below uplifting crust). The uplift generates amass change, which produces a time variation of the gravity field. The deglaciation and changes in the subsurfacehydrologic budget, also generate a mass change, which sums to the tectonic change. Satellite remote sensingis useful in determining the shrinking outlines of glaciers, using both multispectral imaging as well as Radarobservations, thus allowing to determine the surface geometry change. The essential value for climate change andestimate of the hydrologic budget is though the total volume budget estimate, which requires also the thicknessvariation. Remote sensing catches the surface height changes, but these must be corrected for the crustal uplift. Thegeodetic measurements of the crustal dynamics of the Alpine and Himalayan mountain ranges in terms of heightand gravity changes, are therefore in close relation to the estimate of the climatic changes inducing glacier andhydrologic budget changes. We estimate the hydrologic and glacier signal for the Alps and Himalaya-Tibet, usingresults from remote sensing and subsurface hydrologic observations, where available (for the methodologicalrationale see Chen et al. 2018). We estimate the contribution of the dynamic uplift by direct observations ofGNSS. We find that the hydrologic and glacier gravity signal calculated at satellite heights of GRACE andGOCE are superposed to the tectonic signal, and discuss to which amount the signals can be resolved by gravitymeasurements. We compare the predicted signals with the satellite observations of GRACE and GOCE, findingthat the tectonic uplift signal is small relative to the expected glacier/hydrologic signals, but that it cannot beneglected. We define the requirements to future gravity satellites in order to make a significante contribution to thedetection of hydro-glacial mass changes and the separation of the tectonic signal.Reference:Chen W., Braitenberg, C., Serpelloni, E. (2018) Interference of tectonic signals in subsurface hydrologic monitor-ing through gravity and GPS due to mountain building, Global and Planetary Change, Volume 167, August 2018,Pages 148-159
Interactive comment on “Time – lapse gravity and levelling surveys reveal mass loss and ongoing subsidence in the urban subrosion prone area of Bad Frankenhausen/Germany” by Martin Kobe et al.
Full text linkDuring four years (2014-2018) repeated gravity measurements have been made together with repeated leveling in an area in Germany affected by sink-holes. The formation of sink-holes and ground subsidence is a hazard in many areas, also in North-East Italy. The study poses the question whether the subsurface mass-loss associated to the subsurface erosion is measurable by repeated gravity measurements
Maria Zadro
No full textMaria Zadro è stata Professore Ordinario di Fisica Terrestre presso l'Università di Trieste, nei due Corsi di Laurea di Geologia e di Fisica. Per molti anni ha investito la carica di Direttore dell'Istituto di Geodesia e Geofisica della medesima Università, ed ha coordinato il Dottorato di Ricerca in Geofisica della Litosfera e Geodinamica dall'anno della sua istituzione. Le registrazioni dei pendoli della Grotta Gigante sono state esaminate da Maria Zadro a partire dalle prime osservazioni, identificando le deformazioni indotte dalle maree terrestri e dal carico oceanico, dalle oscillazioni libere della terra generate dal maggior evento sismico mai registrato, il terremoto del Cile 1960, e dai segnali preomonitori del terremoto del Friuli del 1976. Nel 1977 ha installato la rete clino-estensimetrica del Friuli, che era dotata di 5 stazioni geodetiche localizzate a Barcis, Gemona, Villanova delle Grotte, Invillino e Cesclans e delle quali è ancora attiva la stazione di Villanove delle Grotte. Altro tema di studio innovativo sono state le proprietà spettrali del potenziale gravitazionale, approccio che porta alcuni vantaggi nella modellazione delle strutture del sottosuolo rispetto alla formulazione del dominio dello spazio. Maria Zadro ha collaborato con molte istituzioni internazionali e nazionali, ed ha mantenuto contatti duraturi con colleghi dalla Cina, Russia, Sud America, Austria e Germania. Ha fatto una generosa donazione all'Università di Trieste, per l'istituzione di borse di studio di Dottorato in campo geodetico-geofisico, che permetteranno gli studenti a dedicarsi all'applicazione di metodologie geodetiche per la comprensione di processi fisici che riguardano la terra, continuando l'ambito degli studi intrapreso da Maria Zadro
Geodetic observations to monitor natural hydraulic overpressure
Full text linkThe pressurization of a channel system occurs naturally through intake of rainfall and river drainage. The consequences of up to 1MPa pressurization include sudden uprise of water level, blockage of channels, increased erosion and possible triggering of seismicity, with associated diversified hazards. We model the expected deformation with the Finite Element Method and analytical approaches, and find that the pressures induce deformation which can be geodetically detected. The careful analysis of GNSS timeseries and tilt observations recovered in N-Italy demonstrates that the signals are observable. The observations of tilt have been made in karstic caves where a GPS station has been colocated on the surface. The uplift of GPS during underground floods is expected to be up to several mm and the titling at the microradians level for the tiltmeters. The results demonstrate that geodetic observations could be used to monitor internal pressure loading of the underground channel system. The research is based on the results described in Grillo et al. 2018 and Braitenberg et al. 2019.
References
Braitenberg C., Pivetta T., Barbolla D.F., Gabrovšek F., Devoti R., Nagy I. (2019) Terrain uplift due to natural hydrologic overpressure in karstic conduits, Scientific Reports, in press.
Grillo B., Braitenberg C., Nagy I., Devoti R., Zuliani D., Fabris P. (2018). Cansiglio Karst-Plateau: 10 years of geodetic-hydrological observations in seismically active northeast Italy. Pure and Applied Geophysics, Volume 175, Issue 5, 1765-1781, doi:10.1007/s00024-018-1860-7
The deforming and rotating Earth – A review of the 18th International Symposium on Geodynamics and Earth Tide, Trieste 2016
Full text linkThe 18th International Symposium on Geodynamics and Earth Tides 2016 covered phenomena that
generate temporal variations in geodetic and geophysical observations. In calculating the stress
field for Earth tides, the observed geodetic response is used for defining the Earth's rheology, the Earth internal
structure, Earth rotation parameters, and the functioning of the sophisticated instrumentation mounted
on Earth and satellites. The instrumentation capable of observing Earth tides, measures changes
generated by lithospheric plate movements, as the earthquake cycle and volcanism. Hydrology, tem-
perature, and pressure, either of natural or anthropogenic origin, affect the high precision observations,
and therefore must be included in this study-realm
A geothermal application for GOCE satellite gravity data: modelling the crustal heat production and lithospheric temperature field in Central Europe
Full text linkSince 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
Detectability of Seamount Eruptions Through a Quantum Technology Gravity Mission MOCAST+: Hunga Tonga, Fani Maoré and Other Smaller Eruptions
Full text linkSeamount eruptions alter the bathymetry and can occur undetected due to lack of explosive character. We review documented eruptions to define whether they could be detected by a future satellite gravity mission. We adopt the noise level in acquisitions of multi-satellite constellations as in the MOCAST+ study, with a proposed payload of a quantum technology gradiometer and clock. The review of underwater volcanoes includes the Hunga Tonga Hunga Ha’apai (HTHH) islands for which the exposed surface changed during volcanic unrests of 2014/2015 and 2021/2022. The Fani Maoré submarine volcanic eruption of 2018–2021 produced a new seamount 800 m high, emerging from a depth of 3500 m, and therefore not seen above sea surface. We review further documented submarine eruptions and estimate the upper limit of the expected gravity changes. We find that a MOCAST+ type mission should allow us to detect the subsurface mass changes generated by deep ocean submarine volcanic activity for volume changes of 6.5 km3 upwards, with latency of 1 year. This change is met by the HTHH and Fani Maoré volcanoes
Sensitivity of gravity and topography regressions to earth and planetary structures
Full text linkThe availability of global gravity fields and topography through calculation services like the International Centre for Global Earth Models, allows easy access to gravity data, greatly enlarging the spectrum of users. The applications extend much farther than the classic modeling through the gravity-specialist. We investigate the sensitivity of the joint analysis of topography and gravity data based on linear regression analysis and clustering of the response to particular characteristics of the lithosphere structure. The parameters of the regression analysis are predicted to have characteristic values, which allow to distinguish continental crust from oceanic crust, and signalize the presence of crustal inhomogeneity. Predictions are made through theoretical considerations and on synthetic models. We use the South Atlantic Ocean and the confining South American and African continents for illustration, where the regression parameters distinguish oceanic crust from the ridge up to the bathymetric inflection point, from the transitional crust and the continental crust, allowing to map these units. The general properties of the parameters are statistically relevant, since the errors on the parameters are less than 10% the amplitude of the parameters. We compare the regression parameters with those produced by a global crustal model (CRUST1.0), and find good correspondence between the observed and predicted fields. The analysis can be applied with machine learning algorithms, without the need of specific forward or inverse gravity modeling skills. It is therefore particularly useful in view of the enhanced access to the data through the calculation service, and could be implanted as an add-on tool, since it allows to efficiently distinguish isostatic contribution to the gravity field from crustal sources. Given the experience on the gravity field of the Earth, the analysis can be analogously extended to other planets. For illustration, we show that for Mars a coherent class of Martian crust can be identified
Constraining the continental crust heat production with a gravimetric Moho
Full text linkSatellite-only global gravity models (GGMs) offer an unparalleled homogeneity in coverage and data quality.
Solutions including the gradiometry data from the GOCE mission reach high resolutions (degree and order up
to 200 and above), which have already proven adequate in resolving the geometry of crustal structures (e.g. the
Moho morphology). We enquire to what extent an estimate of the crustal radiogenic heat production based on
crustal thickness as sensed through gravity can provide predictive results.
These characteristics make GGMs a promising candidate in solving two issues affecting the available sur-
face heat flow measurements: those affecting the spatial sampling, which is often inhomogeneous and biased
(so care must be taken in interpolations) and those concerning the superposition of components, which cannot
be uniquely isolated from heat flow alone. Stripping the crustal component from the measurements is of utmost
importance both "downwards", in modelling the lithospheric thermo-mechanical structure and sublithospheric
dynamics, and "upwards", when assessing the near-surface (i.e. above basement) thermal regime in energy
applications.
Choosing a least-structure inversion strategy (i.e. gravity anomaly to Moho depth), to keep the dependence
on other observables as limited as possible, we enquire with a set of synthetic experiments the sensitivity of
estimates of the heat flow contribution of continental crust against factors deviating from a perfect, static Earth
assumption (such as ongoing dynamics, crustal inhomogeneities not accounted for, thermal refraction). These
tests are carried out both with thermal parameter uncertainties included, to assess their propagation, and without
them, to test if our starting hypotheses are sound. The results show the promising predictive power of even such
a single-observable approach and the extent of the detectability of regional scale thermal regimes using global
gravity products.
Since these aims required a flexible and light modelling framework, we developed a forward thermal mod-
elling tool to estimate the temperature field in the lithosphere (surface to thermal-LAB). It comprises a 3D
finite-difference heat equation solver on non-constant step rectilinear grids, taking into account temperature and
pressure dependent density and thermal conductivity (using a Picard iterative scheme) and relying on a direct
solver based on the Cholesky decomposition (CHOLMOD). The 3D volumes of input parameters are easily
filled in starting from a layer-based model definition. The adopted grid discretisation is coherent with the prism
definition, enabling to evaluate the effect of the same model both in the temperature and bgravity field
Gravimetry for monitoring water movements : the Classic Karst as a natural laboratory
Full text linkThe Karst environment is characterized by a peculiar water system circulation, governed by a network of conduits
in which the water flows. The name Karst is derived from the Classic Karst region which is located across Italy,
Slovenia and Croatia borders. This area gave name to the phenomenon because it was one of the first worldwide
to be studied and it is still object of many researches and hosts an important monitoring network.
In this area the water is supplied mainly by infiltration during the autumn-spring rainfall events but also from the
Reka river that sinks in the Škocjan caves and then flows underground up to the Timavo Springs.
The water path is very well known near the Škocjan cave where the water inflow from the Reka river and the rain
fall are continuously monitored and also the karst conduits have been mapped directly by speleology inspection.
Such data are indispensable in order to construct and constrain 2D hydraulic models that explain very well the
water dynamics in the area.
However in Skocjan the water circulation is superficial while in other parts of the Karst the water flows deeper
underground: in the Grotta Gigante, a natural cave, the water flow is located over 200m below the surface.
Its movement could be hardly monitored by direct observation and also modelling is limited due to the lack of a
3D model of the aquifer. Indirect geophysical methods, in particular gravimetry, could be exploited in order to
obtain some constraints for the underground conduits and cavities and also to gain information about the water
mass movements through time.
In this contribution we present some preliminary synthetic models for assessing the gravity signals expected for
the underground cavities typical for the karstic area. In addition we evaluate the time gravity field change during
strong rainfall events where the water is expected to fill the conduits and cavities. In future we will take advantage
of these models to place a continuous gravity meter that cuold be useful to constrain the water fluxes in area where a direct observation of the water is difficult
- …
