G3.4 | Leveraging Glacial Isostatic Adjustment and other Solid-Earth Deformation Processes for Exploring Earth's Interior
Leveraging Glacial Isostatic Adjustment and other Solid-Earth Deformation Processes for Exploring Earth's Interior
Co-organized by CR5/GD7, co-sponsored by SCAR
Convener: Holger Steffen | Co-conveners: Hilary Martens, Hugo Boulze, Federico Daniel MunchECSECS, Anastasia ConsorziECSECS, Jun'ichi Okuno, Matthias O. WillenECSECS
| Wed, 17 Apr, 10:45–12:30 (CEST)
Room -2.91
Posters on site
| Attendance Thu, 18 Apr, 16:15–18:00 (CEST) | Display Thu, 18 Apr, 14:00–18:00
Hall X2
Posters virtual
| Attendance Thu, 18 Apr, 14:00–15:45 (CEST) | Display Thu, 18 Apr, 08:30–18:00
vHall X2
Orals |
Wed, 10:45
Thu, 16:15
Thu, 14:00
The dynamic response of the solid Earth to the waxing and waning of ice sheets and corresponding spatial and temporal sea-level changes is termed Glacial Isostatic Adjustment (GIA). This process, like solid Earth tides, oceanic load tide, other short-period surface loading (e.g., continental water), and normal-mode oscillations, causes surface deformation and changes in the gravity field, rotation, and stress state of the Earth. Different types of observational data, now standardized, help constrain highly sophisticated models of the Earth. They also serve as a tool to constrain the rheological properties of the Earth.

We aim to bring together researchers working on GIA, body tides, short-period loading problems, and normal modes with the broad goal of using these various processes to better understand the interior of the Earth and other planets across these wide temporal and spatial scales. This session is co-sponsored by the SCAR sub-committee INSTANT-EIS, Earth - Ice - Sea level, in view of instabilities and thresholds in Antarctica (https://www.scar.org/science/instant/home/).

Session assets

Orals: Wed, 17 Apr | Room -2.91

Chairpersons: Matthias O. Willen, Anastasia Consorzi, Hugo Boulze
On-site presentation
Volker Klemann, Meike Bagge, Robert Dill, Jan M. Hagedoorn, Zdeněk Martinec, and Henryk Dobslaw

Surface deformations due to changes in the rotation of the Earth are significantly impacted by glacial isostatic adjustment (GIA). The long-term trend of polar motion contributes to global observations like that of the current satellite gravity mission GRACE-FO. The theory and how to apply this contribution to correct GRACE observational data is well understood and goes back to the concise studies of Mitrovica et al. (2005) and Wahr et al. (2015), respectively. According to the International Earth Rotation Service (IERS), a standard correction method is suggested, where the observed long-term trend of the polar motion is considered to originate from GIA. Recent studies show that the modelled GIA contribution to polar motion strongly depends on structural features of the Earth's interior as well as on the glacial history. Other processes like mantle convection or more recent climatic processes are attributed to contribute as well (Adhikari et al. 2018).

In this presentation we focus on the impact of the Earth's viscosity structure on the modelled polar motion. In addition to its radial stratification, we discuss the influence of lateral variability. We apply the numerical 3D viscoelastic lithosphere and mantle model VILMA, which solves the gravitationally self-consistent field equations in a spherical geometry, and which considers the rotational feedback and the sea-level equation. The theory of Martinec and Hagedoorn (2014) applied here is not based on the normal mode theory, but solves the field equations in the time domain. We show the consistency of the chosen approach and rate the influence of lateral changes in viscosity against the impact of radial viscosity stratification. The study was motivated by the ESA Third Party Mission 'GRACE-FO' and contributes to the German Climate Modelling Initiative 'PalMod'.

Adhikari, S, Caron L, Steinberger, B, ..., Ivins, ER (2018). What drives 20th century polar motion? Earth Planet. Sci. Lett. doi:10.1016/j.epsl.2018.08.059
Martinec, Z, Hagedoorn, JM (2014). The rotational feedback on linear-momentum balance in glacial isostatic adjustment. Geophys. J. Int. doi:10.1093/gji/ggu369
Mitrovica, JX, Wahr, J, Matsuyama, I, Paulson, A (2005). The rotational stability of an ice-age earth. Geophys. J. Int. doi:10.1111/j.1365-246X.2005.02609.x
Wahr, J, Nerem, RS, Bettadpur, SV (2015). The pole tide and its effect on GRACE time-variable gravity measurements: Implications for estimates of surface mass variations. J. Geophys. Res. Solid Earth. doi:10.1002/2015JB011986

How to cite: Klemann, V., Bagge, M., Dill, R., Hagedoorn, J. M., Martinec, Z., and Dobslaw, H.: Polar motion of a 3D viscoelastic earth model: Consequences for GIA signals in GRACE-FO, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5642, https://doi.org/10.5194/egusphere-egu24-5642, 2024.

On-site presentation
William Scott, Mark Hoggard, Sia Ghelichkhan, Angus Gibson, Stephan Kramer, and Rhodri Davies

Melting ice sheets transfer water from land into ocean basins. The resulting sea-level rise is, however, highly spatially non uniform and time dependent due to complex feedbacks between viscoelastic deformation of the solid Earth in response to these evolving surface loads and coupled perturbations in the gravitational field and rotation axis. Together, these processes are referred to as Glacial Isostatic Adjustment (GIA) and accurate models of GIA are crucial for robust interpretation of both modern and paleo measurements of sea-level change and ice-mass balance. 

A limitation with many existing GIA modelling codes is their inability to incorporate lateral variations in Earth structure. Nevertheless, there is mounting evidence for the presence of significant lateral changes in mantle viscosity, for example beneath West Antarctica, that give rise to complex interactions between rates of surface rebound, sea-level change and ice retreat. Understanding these processes requires development of a new generation of GIA codes capable of handling such variations in rheology at increasingly fine spatial and temporal evolution. 

In this presentation, we will introduce a new project to model GIA using the Firedrake finite element framework and present results for several community benchmarks. Firedrake leverages automatic code generation to create a separation of concerns between employing the finite-element method and implementing it. This approach maximises the potential for collaboration between computer scientists, mathematicians, scientists and engineers and enables sophisticated high performance simulations. A key advantage of Firedrake is the automatic availability of sensitivity information through the adjoint method, allowing us to investigate inverse problems. We are developing an open-source tool highly suited to the challenge of modelling complex Earth structure in GIA, building on the Firedrake-based G-ADOPT project for mantle convection. We envision that future applications might include, but are not limited to, investigating non-linear and transient rheologies, feedbacks between sea-level and glacier dynamics, and reducing uncertainty on sea-level projections into the future. 

How to cite: Scott, W., Hoggard, M., Ghelichkhan, S., Gibson, A., Kramer, S., and Davies, R.: Modelling Glacial Isostatic Adjustment in Firedrake , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6863, https://doi.org/10.5194/egusphere-egu24-6863, 2024.

On-site presentation
Erica Lucas, Natalya Gomez, Konstantin Latychev, and Maryam Yousefi

West Antarctica is underlain by a laterally heterogenous upper mantle, with localized regions of mantle viscosity reaching several orders of magnitude below the global average. Accounting for 3-D variability in upper mantle structure in glacial isostatic adjustment (GIA) simulations has been shown to significantly impact the predicted spatial rates and patterns of crustal deformation, geoid and sea-level changes. Uncertainty in constraining the viscoelastic structure of the solid Earth remains a major limitation in GIA modeling. To date, investigations of the impact of 3-D Earth structure on GIA have adopted solid Earth viscoelastic models based on global- and continental-scale seismic imaging with variability at spatial scales >150 km. However, regional body-wave tomography shows mantle structure variability at smaller spatial scales (~50-100 km) in central West Antarctica (Lucas et al., 2020). Here, we investigate the effects of incorporating this smaller-scale lateral variability in upper mantle viscosity into 3-D GIA simulations. Lateral variability in upper mantle structure at the glacial basin scale is found to have a significant impact on GIA model predictions, especially in coastal regions undergoing rapid ice mass loss. For example, incorporating a transition from lower viscosity at the mouth of Thwaites Glacier to higher viscosity further upstream impacts the predicted rate and pattern of solid Earth deformation and sea-level change in response to ongoing and projected ice mass loss, with possible implications for the evolution of the overlying ice and the interpretation of geophysical observables.

How to cite: Lucas, E., Gomez, N., Latychev, K., and Yousefi, M.: The impact of regional-scale variability in upper mantle viscosity on GIA in West Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13928, https://doi.org/10.5194/egusphere-egu24-13928, 2024.

On-site presentation
Dustin Schroeder, Jasmin Falconer, and Matthew Siegfried

Our capacity to estimate vertical motion of the solid Earth with high precision has transformed our understanding of a variety of Earth processes, including mantle dynamics, plate tectonics, volcanic hazards, earthquake rupture, and surface-water balance. Geodetic observations of solid Earth deformation were first achieved on land with conventional surveying techniques, global navigation satellite system (GNSS) deployment, and satellite remote sensing, then expanded to the global ocean with seafloor geodesy techniques like GNSS-Acoustic (GNSS-A) experiments and fiber-optic sensing. Although we can now assess solid Earth deformation nearly everywhere on Earth, we still have not achieved subglacial geodesy: directly observing uplift or subsidence beneath glaciers and ice sheets. Due to decreasing ice mass, we expect high rates of uplift beneath Earth’s ice masses (i.e., glacial isostatic adjustment, or GIA), but available GNSS observations from exposed rock on the periphery of the Greenland and Antarctic ice sheets suggest uplift rates can be highly variable on 10s of km length scales. Recent observational and modeling studies have suggested that GIA could provide a critical stabilizing feedback for ice-sheet mass loss on decadal and centennial timescales, therefore developing and deploying the technology needed for subglacial geodesy is critical for accurate projections of sea level change, particularly in Antarctica where areas of exposed bedrock are rare. To address this challenge, we present a suite of combined radar sounding / GNSS experiments and systems under development to constrain uplift rates beneath both slow-flowing (< 10 m/yr) and fast-flowing ( > 10 m/yr) ice. We also discuss a range of related systems and experiments under development to constrain and correct for potentially confounding firn compaction signals.

How to cite: Schroeder, D., Falconer, J., and Siegfried, M.: Enabling Subglacial Geodesy Through High-Precision Radar Sounding and GNSS Time Series Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-25, https://doi.org/10.5194/egusphere-egu24-25, 2024.

On-site presentation
Jean-Paul Boy and Vagif Taghiyev

We compute daily GPS solutions for about 200 permanent stations in Greenland, Scandinavia and Canada for the 2000 – 2023 period, using the CNES/GINS software in precise point positioning with integer ambiguity resolution (IPPP) mode. The observed vertical displacements are caused by both past- and present-day ice mass (PDIM) changes. The glacial isostatic adjustement (GIA) is the visco-elastic Earth’s response to the Pleistocene glaciation and deglaciation, whereas the PDIM is often estimated assuming an elastic Earth’s response.

We revisit the problem of the separation of GIA and PDIM using state-of-the-art ice models (for example, ICE-6G and ICE-7G) and observations from space gravimetry (GRACE and GRACE Follow On) and altimetry (CryoSat-2 and ICESat-2).

In particular, we investigate different rheology models, including the classical Maxwell model used in GIA modeling, but also the Burgers model allowing transient anelastic deformation at timescales of 10 to 20 years.

We found that the Burgers model with a transient viscosity of about 1018 Pa.s in the upper mantle, combined with the VM5a or VM7 viscosity profiles (Maxwell component) is in better agreement with the observed GPS vertical displacements.


How to cite: Boy, J.-P. and Taghiyev, V.: Vertical deformation in Greenland: separation of past and present-day ice mass loss contributions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12953, https://doi.org/10.5194/egusphere-egu24-12953, 2024.

On-site presentation
Valentina R. Barletta, Andrea Bordoni, and Shfaqat Abbas Khan

Currently, many different glacial isostatic adjustment (GIA) models have been proposed for Greenland, as a consequence of a still largely unknown deglaciation there. GNSS trends are often used to constrain GIA models regionally. However, the GNSS uplift rates contain a large contribution from present-day mass changes (mostly due to ice melting) that must be removed to extract the GIA uplift rates. The elastic uplift rates estimates are potentially affected by uncertainties. They depend on the Earth model chosen (usually PREM-based models) and on high-resolution mass changes estimates, usually obtained from volume changes measured with altimetry. The volume changes need to be converted into mass variations, mostly using models (surface mass balance and firn compaction models) that can introduce biases. Since the elastic uplift rates are proportional to the mass changes, any uncertainty in the mass variations directly affects the elastic uplift rates eventually, as well as the GIA GNSS residuals uplift rates obtained from them. And in turn, these biases reflect directly in the GIA models constrained with those GNSS.

Here we propose a novel additional GIA constraint based on both GRACE and GNSS observations. We start from a very simple model, based on three basic and general assumptions: 1) Elastic uplift rates at a given distance from a mass distribution (e.g. a disk changing height) are proportional to the mass variation. 2) The GIA induced uplift rates can be considered proportional to the apparent mass changes produced by GIA gravity changes (e.g. Wahr et al 2000 and Riva et al. 2009). 3) The total uplift rate measured by a GNSS is the sum of the elastic uplift rate caused by any surface mass changes and the GIA induced uplift rate (assuming that uplifts rates due to plate tectonics are negligible in Greenland). We then show that this simple model can be applied to Greenland, and still retain most of its validity. The three points above become three equations in four unknowns, namely the surface mass changes and the related elastic uplift rate, the GIA uplift rate and its related apparent mass change.  Using the average uplift rate measured by the whole GNET (Greenland GNSS Network) and the total GMB (Greenland Mass Balance) measured with GRACE, from the three equations we derive a global consistency relation between the average GIA uplift rate and its related apparent mass change for the whole Greenland.

In this way, the combined analysis of the GMB from GRACE and GNET provides a very solid constraint for Greenland-wide GIA models. GIA models constrained only regionally might provide estimates that are not consistent in other Greenland regions. The four GIA models that we tested do not respect the consistency relation we found. This relation does not allow to determine the GIA uplift rate uniquely, but we show that together with some basic considerations about the plausible deglaciation scenarios, it allows to identify a reasonable range for the GIA component in the average GNSS uplift rate.

How to cite: Barletta, V. R., Bordoni, A., and Khan, S. A.: GIA constraints for Greenland from combined GRACE and GNSS observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13658, https://doi.org/10.5194/egusphere-egu24-13658, 2024.

On-site presentation
Maaike F. M. Weerdesteijn and Clinton P. Conrad

Along the periphery of the Greenland ice sheet, Global Navigation Satellite System (GNSS) stations observe uplift of a few mm/yr, reflecting Earth’s response to past and contemporary changes in Greenland’s ice mass. On the coast of southeast Greenland, near the Kangerlussuaq glacier, GNSS stations show abnormally rapid ground uplift, faster than 10 mm/yr. Current earth deformation models, which employ a layered Earth structure, cannot explain such rapid uplift. Here we develop 3D regional models of uplift in response to deglaciation occurring over timescales corresponding to the last glacial cycle (past 1000s of years), the last millennium (past 100s of years), and recent rapid deglaciation (past 10s of years). These 3D models incorporate a track of low-viscosity upper mantle and thin lithosphere, consistent with the passage of Greenland over the Iceland plume during the past ~50 Myr. We find that the fastest ground uplift occurs where rapid deglaciation occurs above the low-viscosity plume track of the Iceland plume. This uplift reflects viscous deformation of the upper mantle, and is much larger than the (instantaneous) elastic deformation that also results from this deglaciation. Above the low-viscosity plume track, the uplift contribution is greatest for the most recent deglaciation (past decades), followed by the contribution from deglaciation during the last millennium. The combination of these viscous contributions can explain uplift observations of more than 10 mm/yr near the rapidly deglaciating Kangerlussuaq glacier, which lies above the Iceland plume track, and slower uplift in the surrounding areas. Rapid uplift observed to the south of the Kangerlussuaq glacier can be explained if the low-viscosity plume track extends farther southward beneath the Helheim glacier, which is also rapidly deglaciating. Such rapid viscous uplift from recent and local ice melt is not usually considered in glacial isostatic adjustment (GIA) models, but likely happened in the past in response to previous deglaciation. It will also become increasingly important in the future as deglaciation accelerates.

How to cite: Weerdesteijn, M. F. M. and Conrad, C. P.: Rapid Earth uplift in southeast Greenland driven by recent ice melt above low-viscosity upper mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5748, https://doi.org/10.5194/egusphere-egu24-5748, 2024.

Virtual presentation
Tanghua Li, Timothy Shaw, Nicole Khan, F. Chantel Nixon, W. Richard Peltier, and Benjamin Horton

The Arctic has been key area for glacial isostatic adjustment (GIA) studies because it was covered by large ice sheets at the Last Glacial Maximum. Previous GIA studies applied mainly 1D Earth models. The few studies that did include 3D Earth structures have not considered the lateral heterogeneity differences across different regions of the Arctic. Here, using the latest standardized deglacial relative sea-level (RSL) databases from Norway and Russian Arctic, we investigate the effects of 3D structure on GIA predictions and explore the magnitudes of the lateral heterogeneity in both regions.

The 3D Earth structure consists of 1D background viscosity model (ηo) and lateral viscosity variation, the latter is derived from the shear velocity anomaly from seismic tomography model and controlled by scaling factor (ß) denoting the magnitude of lateral heterogeneity.

The Norway RSL database includes 413 sea-level index points (SLIPs), 175 marine limiting data and 433 terrestrial limiting data, while the Russian Arctic database includes 353 SLIPs, 78 marine limiting data and 92 terrestrial limiting data.

We find 3D Earth structures have significant influences on RSL predictions and the optimal 3D model notably improves the fit with RSL data. However, we realize RSL data from Norway and Russian Arctic prefer different 3D structures to provide the best fits. The Russian Arctic database prefers a softer background viscosity model (ηo), but larger scaling factors (ß) than those preferred by Norway database. We further test the extent to which the 3D structure can be eliminated by refinement of ice model.

How to cite: Li, T., Shaw, T., Khan, N., Nixon, F. C., Peltier, W. R., and Horton, B.: The lateral heterogeneity of Glacial Isostatic Adjustment modelling across the Arctic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5259, https://doi.org/10.5194/egusphere-egu24-5259, 2024.

On-site presentation
Elisabeth Seidel, Holger Steffen, Rebekka Steffen, Niklas Ahlrichs, and Christian Hübscher

Increasing and decreasing ice masses cause an isostatic adjustment of the crust, which can trigger fault reactivation. It could be assumed that the higher the ice load, the stronger the glacially induced fault reactivation, leading to stronger earthquakes. Here we focus on glacially triggered fault reactivation in the southern Baltic Sea over the past 200,000 years (since the Upper Saalian). Our study area comprises the Caledonian Suture Zone between the East European Craton and the West European Platform as well as the trans-regional Tornquist Zone. Consequently, it reflects a polyphase tectonic history. The fault zones and systems in this geoarchive have been mapped and studied through several reflection seismic investigations. They display variations in their characters, strike and dip directions, age, and depths, documenting the complex evolution.

We focus on faults indicating reactivation during the Quaternary, determined by the seismic sections. After documenting their fault properties, we calculated the glacially induced Coulomb Failure Stress changes (∆CFS) at the faults over the past 200,000 years using finite-element simulations of various glacial isostatic adjustment models. The results show significant local and temporal differences in fault reactivation. We observe that shorter ice advances and lower ice loads correlate with higher ∆CFS, suggesting a higher potential for fault reactivation, which could potentially lead to stronger earthquakes if released in one event. Moreover, we will discuss if the lateral ice thickness gradient or the steepness of the flanks of the ice sheet might play a major role.

How to cite: Seidel, E., Steffen, H., Steffen, R., Ahlrichs, N., and Hübscher, C.: Does thicker ice cover cause stronger glacially triggered earthquakes? - A case study from the southwestern Baltic Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16655, https://doi.org/10.5194/egusphere-egu24-16655, 2024.

On-site presentation
Andrei Dmitrovskii, Federico Munch, Christian Boehm, Hilary Martens, and Amir Khan

Ocean tide loading (OTL) brings about recurring deformation of the Earth’s surface. Some of the OTL harmonics, e.g. M2, O1, Mf, cause sufficiently large surface displacement to be registered by the Global Navigation Satellite Systems (GNSS). These displacements are sensitive to the interior structure of the planet in a broad range of temporal and spatial scales making them a potentially unique source of information about the planet’s response at low frequencies. Comparison between observations and predictions for 1D elastic Earth models result in discrepancies of up to 3 mm (Bos et al., 2015, Martens et al., 2016). Spatial coherency of these discrepancies hints to 3D interior structure as one of the main sources of such residuals.
In this context, we present a framework to invert OTL observations for 3D crustal and mantle structure based on a trust-region Newton-type iterative algorithm. Furthermore, we resort to the adjoint approach as an efficient means of computing the gradient for the high-dimensional model space. Focusing on the design of the inverse algorithm, we constrain ourselves to deformations of an isotropic elastic planet, which are governed by a self-adjoint forward operator. In order to assess the robustness of the method, we perform a suite of 3D synthetic inversions that mimic the distribution of the GNSS stations in South America. Preliminary results indicate enhanced sensitivities to the crustal and upper mantle density and elastic properties in the vicinity of the coastlines.

How to cite: Dmitrovskii, A., Munch, F., Boehm, C., Martens, H., and Khan, A.: Towards imaging 3D crust and mantle structure by means of ocean tidal loading tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10834, https://doi.org/10.5194/egusphere-egu24-10834, 2024.

Posters on site: Thu, 18 Apr, 16:15–18:00 | Hall X2

Display time: Thu, 18 Apr 14:00–Thu, 18 Apr 18:00
Chairpersons: Jun'ichi Okuno, Hugo Boulze, Federico Daniel Munch
Antarctic Geothermal Heat Flow, Crustal Conductivity and Heat Production Inferred From Seismological Constraints on Crustal Composition and Lithospheric Thermal Structure
James Hazzard and Fred Richards
Jun'ichi Okuno, Akihisa Hattori, Koichiro Doi, Yoshiya Irie, and Yuichi Aoyama

The history of ice melting and the viscoelastic properties of the mantle heavily influence Antarctic crustal deformation caused by Glacial Isostatic Adjustment (GIA). The interaction between ice history and mantle viscosity further complicates the complex Antarctic GIA. Nonetheless, geodetic observations, such as GNSS, are crucial for constraints on the GIA model parameters.

For over two decades, the Japanese Antarctic Research Expedition (JARE) has been using GNSS and absolute gravity measurements to obtain data along the coast of Lützow-Holm Bay, primarily at Syowa Station. This study examines the geodetic signals associated with GIA from observations along the Lützow-Holm Bay coastline in East Antarctica, and we also conduct GIA simulations based on the recent report of rapid ice thinning in the target region during the mid-Holocene.

Based on geomorphological surveys and surface exposure ages, Kawamata et al. (2020: QSR) showed that the region experienced rapid ice thinning of over 400 m from about 9 to 6 ka. Representative deglaciation models, such as ICE-6G, do not account for this rapid thinning process. Therefore, we investigate the variability of the geodetic signals using the ice history, including this rapid thinning. Our predictions demonstrate that incorporating the modified ice history results in consistent outcomes with the observations. This finding supports the notion that rapid ice melting occurred in the Holocene and suggests that geodetic observations can help constrain this region's ice sheet melting process. Additionally, we will present a possibility of the readvance following the rapid retreat based on the precise GIA modelling.

How to cite: Okuno, J., Hattori, A., Doi, K., Irie, Y., and Aoyama, Y.: Mid-Holocene ice history inferred from GIA-induced crustal motion around Lützow-Holm Bay, East Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6898, https://doi.org/10.5194/egusphere-egu24-6898, 2024.

Kim de Wit, Roderik S.W. van de Wal, and Kim M. Cohen

The evolution of the Holocene coastal plain in the Netherlands is strongly influenced by global sea-level rise and regional subsidence patterns. Added up these components are known as relative sea-level rise (RSLR), and explain the coastal plain build-up and accommodation space. Due to RSLR, geological indicators of gradual-drowning formed, such as basal peat layers. These indicators have been sampled and dated from different depths and locations across the coastal plain and are used to document rising coastal sea levels and inland groundwater levels. Databasing and spatial-temporal analysis of the large set of indicators (N=~720) serves to assess local and regional variabilities in RSLR.

Collection of geological water level indicators in the Netherlands started as early as the 1950ies. It was carried out for various purposes: RSLR reconstruction, geological mapping of the coastal-deltaic plain, wetland paleoenvironmental reconstructions. Full formal overview of this data did not exist, as past reviews and data compilations (N=50-300) were subregion restricted and usage specific. Regional differences within the Netherlands, e.g. greater RSLR in the north than in the SW, are also long noticed, and mostly attributed to  differential subsidence as caused by glacial isostatic adjustment (GIA: Scandinavian forebulge collapse, at non-linear rate) and longer-term North Sea Basin tectono-sedimentary subsidence (at a linear rate).

Here, we present a uniform database of Holocene coastal plain water level indicators for the Netherlands, using the HOLSEA workbook format. By compiling a database of geological water level indicators, with an explicit and consistent  standardized treatment of dealing with vertical uncertainties, age uncertainties, and indicative meaning of each indicator (e.g. does it resemble former inland  groundwater level, or former sea-level), we enable more accurate break down of differential subsidence and its source components.

Database compilation included documentation of all vertical corrections applied, such as for water depth, (paleo-)tides, long-term background land motion and for compaction, as well as the propagation of uncertainties associated with these corrections.  The ~720 indicators are further categorized into sea level index points (SLIPs), sea-level upper limiting data (ULD) and sea-level lower limiting data (LLD). ULD data is further categorized to separate tidally, river gradient and local-hydrology influenced indicators. Vertically corrected relative sea-level positions and relative groundwater-level positions are reported separately.

Spatial-temporal analysis of the Holocene water level data allowed for an interpolated reconstruction of Holocene RSLR, resulting in map-output that has continuous coverage of the Dutch coastal plain. Furthermore, this data-driven RSLR reconstruction is used to further disentangle components of RSLR: the Holocene water level rise part versus the two main land subsidence parts, independently from global sea-level analysis, basin-geological subsidence reconstructions and geophysical GIA-modelling  output.  We  compare our reconstructed sea level plains to the RSLR output of glacio-isostatic adjustment modelling, which incorporate ice sheet deglaciation history and Earth-rheological models. This enhances our ability to quantify the contributions of GIA and basin subsidence to past and ongoing RSLR and subsidence in the Netherlands.

How to cite: de Wit, K., van de Wal, R. S. W., and Cohen, K. M.: Holocene water-level indicator database for the Dutch coastal plain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7839, https://doi.org/10.5194/egusphere-egu24-7839, 2024.

Vivi Kathrine Pedersen, Natalya Gomez, Jerry X. Mitrovica, Gustav Jungdal-Olesen, Jane Lund Andersen, Julius Garbe, Andy Aschwanden, and Ricarda Winkelmann

Over geological time scales, the combination of solid-Earth deformation and climate-dependent surface processes have resulted in a distinct hypsometry (distribution of surface area with elevation), with the highest concentration of surface area focused near the present-day sea surface. However, this distinctive signature of Earth’s hypsometry does not constitute a single well-defined maximum at the present-day sea surface (0 m). Earth’s hypsometry also shows a prominent maximum ~5 m above the present-day sea surface. Here we explore the nature of this 5-m maximum and examine how it evolved over the last glacial cycle and may evolve moving towards a near-ice-free future. We find that the current elevation of this 5-m hypsometric maximum cannot be explained by ongoing sea-level adjustments following the last glacial cycle. Instead, we suggest that global sea level must have been higher for a significant portion of Earth’s recent multi-million-year history. Indeed, global sea level must have been higher by as much as ~9.5 m to bring this hypsometric maximum in accordance with the sea surface, to account for glacial isostatic adjustments such as ocean syphoning. This signifies that our current polar ice-sheet and sea-level state (and our global reference level) should be considered an anomaly in a geological perspective.

How to cite: Pedersen, V. K., Gomez, N., Mitrovica, J. X., Jungdal-Olesen, G., Andersen, J. L., Garbe, J., Aschwanden, A., and Winkelmann, R.: Earth’s hypsometry and what it tells us about global sea level, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15498, https://doi.org/10.5194/egusphere-egu24-15498, 2024.

Per Knudsen, Carsten Bjerre Ludwigsen, Ole Baltazar Andersen, Matt King, and Christopher Watson

Elastic vertical land movement (eVLM) is the lithosphere's immediate elastic response to the loading and unloading of the Earth's surface mass. Understanding eVLM is crucial for interpreting relative sea level changes, particularly in coastal regions where subsidence or uplift can significantly alter the impacts of sea level changes recorded by tide gauges. Here we present a comprehensive global eVLM model, offering valuable insights for geodesy and related fields, especially in assessing observations from tide gauges and GNSS.

Our eVLM model spans from 1900 to 2022, featuring a 0.5-degree spatial resolution. It provides annual data from 1900 to 1990 and monthly data from 1991 to 2022, enabling both long-term and seasonal assessment. The dataset is available in three different reference frames: Centre of Mass (CM), Centre of Figure (CF), and ITRF2020, and thus suitable for many geodetic applications.

This study incorporates mass change estimations from Greenland, Antarctica, global glaciers, and land water storage (LWS), divided into natural LWS variations and anthropogenic water management like groundwater depletion and dam retention. Thus, we can explain regional VLM patterns that cannot be solely attributed to Glacial Isostatic Adjustment (GIA) models, for example, subsidence across Australia or uplift in Scandinavia that is larger than modeled GIA.

Methodology: We employed a composite loading model, integrating ice models from Greenland (Mankoff et al., 2021) and Antarctica (Otosaka et al, 2022; Nilsson et al, 2022) and glacier models (Hugonnet et al., 2022), GRACE observations, and a land water storage model (Müller-Schmied et al, 2023). Each of the aforementioned five causes of eVLM was perturbed with its uncertainty a thousand times, and the sea level equation was resolved for each variant using the ISSM-SEESAW framework (Adhikari et al., 2016). To align the results with observations in the ITRF2020 reference frame, which mirrors CM on secular timescales and CF on non-secular timescales (Dong et al, 2003). To accommodate this, we applied CM and CF Love loading numbers (Blewitt, 2003) in our calculations, enabling analysis in all three reference frames.

How to cite: Knudsen, P., Ludwigsen, C. B., Andersen, O. B., King, M., and Watson, C.: Causes of Global Elastic Vertical Land Movement from 1900 to 2022, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5655, https://doi.org/10.5194/egusphere-egu24-5655, 2024.

Matt King, Carsten Ankjær Ludwigsen, and Christopher Watson

GPS analysis of Australian vertical land motion (VLM) consistently suggests widespread subsidence of Australia of about 1-1.5mm/yr since ~2000, in contrast to most models of Glacial Isostatic Adjustment which predict motion closer to zero or slightly positive. These GPS findings have been corroborated by estimates from altimeter-minus-tide gauge measurements, suggesting they are robust within their terrestrial reference frame. Here we revisit the potential causes for this misfit, exploring a new reconstruction of global ice-loading changes and its impact on vertical land motion. We show this likely produces a subsidence of Australia of about 0.5mm/yr. We explore this in combination with estimates of hydrological, atmospheric and non-tidal ocean loading displacements. The residual signal is discussed within the context of different GIA model predictions, reference frame errors, and the possible impact of far-field postseismic signal.

How to cite: King, M., Ludwigsen, C. A., and Watson, C.: Towards closing the Australian vertical land movement budget, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4786, https://doi.org/10.5194/egusphere-egu24-4786, 2024.

Sharadha Sathiakumar and Rishav Mallick

Earth’s largest quakes and trans-oceanic tsunamis emanate from subduction zones around the world. Following such large earthquakes, viscoelastic processes and on-fault aseismic fault slip play a crucial role in dissipating the stresses induced by the earthquake, facilitating the solid Earth's return to equilibrium.  The rheological properties of lithospheric rocks govern these postseismic processes and influence time-dependent deformation during the earthquake cycle. Geodetic observations offer an opportunity to constrain these rheological properties, providing valuable insights into the regional lithospheric structure, and potentially improving our understanding of earthquake-related hazards.   

To build intuition for geodetically recorded postseismic deformation, we develop a robust and efficient two-dimensional quasi-static periodic earthquake cycle simulator exploiting the boundary element method and semi-analytical solutions to systems of coupled ordinary differential equations. We investigate the impact of lateral and depth-dependent variations in the viscosity structure of the mantle wedge and the oceanic mantle, to discern their respective contributions and roles in surface deformation observations. We account for the long-term viscous flow rate in the mantle and show that neglecting this term in the earthquake cycle introduces biases in the effective viscosity structure of the lithosphere-asthenosphere system, particularly in the context of power-law rheologies. The low computational cost of our numerical routine makes it ideal for incorporating into future inverse modelling frameworks to estimate regional rheological structure from geodetic observations of subduction zone earthquake cycles.  

How to cite: Sathiakumar, S. and Mallick, R.: A rapid numerical routine for viscoelastic earthquake cycle simulations. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15975, https://doi.org/10.5194/egusphere-egu24-15975, 2024.

Ziheng Yu, Matthew Maitra, and David Al-Attar

To date, most computational work in solid Earth geophysics has been based on linearised continuum mechanics. This is justified so long as deformation from the reference state remains sufficiently small. The dependence on linearisation also reflects computational limitations of the past: most tractable problems relied on geometric symmetries along with linearity to reduce the calculation to the solution of decoupled systems of ordinary differential equations.

Increases in computational power have allowed for increasingly routine applications of fully numerical techniques such as finite-difference, finite-element, and finite-volume methods. This has allowed geophysical problems to be solved in increasingly realistic Earth models. Although for the most part, the equations being solved are the same as linearised ones used previously, keeping nonlinear terms significantly increases the complexity of solution schemes. Within the context of fully numerical methods, non-linear problems are solved using iterative schemes that involve repeated solution of the corresponding linearised equations. This implies that solving non-linear equations should only be appreciably more expensive if non-linear effects are physically important.

Within this presentation, we compare the use of linearised and non-linear equations of motion, focusing on quasi-static elastic and viscoelastic loading problems of relevance to studies of glacial isostatic adjustment. This is achieved using the open-source finite-element package FeniCSx which facilitates rapid development and testing. Starting from simple representative examples, we quantify the errors associated with linearisation along with the added cost of solving non-linear problems.

How to cite: Yu, Z., Maitra, M., and Al-Attar, D.: A comparison of linear and non-linear theories for modelling solid Earth dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3467, https://doi.org/10.5194/egusphere-egu24-3467, 2024.

Marianne Greff-Lefftz and Laurent Métivier

Solid tides, predominantly diurnal and semi-diurnal, are commonly observed on Earth's surface through horizontal and vertical movements (a few tens of centimeters), along with gravity measurements (~100 microgal). This study focuses specifically on tidal effects within the elastic stress field at the surface, which is approximately 1000 Pascals.

We initially established a correlation between tidal elastic pressure and natural hydrogen emission. Hydrogen, in its gaseous form, escaping from Proterozoic basins, represents a potential source of carbon-free energy, leading to extensive research on vents. A notable characteristic of these emissions is the consistent daily cycle observed in specific regions. While atmospheric pressure effects have been shown to account for this cycle, solid tides could serve as an alternative explanation. Considering that tidal waves do not have a uniform spatial distribution on the Earth's surface, we computed time series of elastic pressure at two locations where natural hydrogen emissions are observed: one near the equator in the Sao Francisco basin (Brazil) and another near the North Pole in the Lovozero deposits (Kola Peninsula).

We then explored the maximum shear stress generated by tidal potential in areas experiencing tectonic stresses. We demonstrated that in expansive regions, the maximum shear stress correlates with the peak of the tidal potential, while in compressive regions, it is associated with the minimum tidal peak.

How to cite: Greff-Lefftz, M. and Métivier, L.: Body tides and elastic stresses in the Earth’s crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6485, https://doi.org/10.5194/egusphere-egu24-6485, 2024.

Alex Myhill and David Al-Attar

Long period free oscillation spectra provide one of the main constraints on large-scale lateral structures within the Earth’s mantle. These observations are particularly noteworthy for their direct sensitivity to density variations, which gives them the potential to resolve long-standing questions relating to the nature of the two Large Low Shear Velocity Provinces. However, due to both computational expediency and incomplete theory, there are inaccuracies within existing codes for forward modelling of free oscillation spectra. This has limited the ability of previous studies to reliably infer Earth structure using such observations.

This poster outlines work on a new open-source code for modelling free oscillation spectra within laterally heterogeneous Earth models. We apply a generalised normal mode coupling method that overcomes various limitations with the traditional mode coupling approach. We account fully for the non-linear dependence of the matrix elements on density and boundary topography, and exactly solve the equations of motion. Computational costs have been minimised by using high-performance libraries, and efficient numerical linear algebra, in addition to parallelisation. Our code is also suitable for calculation of sensitivity kernels using the adjoint method. Benchmarks against current codes as well as performance benchmarks are shown to demonstrate the accuracy and efficiency of our new method.

How to cite: Myhill, A. and Al-Attar, D.: Towards exact free oscillation spectra through generalised normal mode coupling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2515, https://doi.org/10.5194/egusphere-egu24-2515, 2024.

He Tang, Wenke Sun, and Yuting Ji

This research presents an innovative semi-analytical method to study the deformation of a viscoelastic, spherical, layered Earth model under periodic loading. We explore the effects of surface mass changes on deformation over various timescales, including annual and interannual, using a linear rheology profile. Our approach leverages a novel set of formulas in the spectral domain, linking mass, geoid, and displacement through complex Love numbers and Stokes coefficients. This technique bypasses the traditional reliance on viscoelastic Green’s functions.

In our analysis, we particularly focus on the impact of annual cyclic mass loading on viscoelastic loading deformation. We consider both steady-state creep and additional transient creep across a broad spectrum of viscosities. Our findings reveal that while steady-state viscosity values, constrained by Glacial Isostatic Adjustment (GIA) data, show minimal viscoelastic impact on annual load deformation, the inclusion of transient creep, primarily informed by post-seismic data and modeled through the Burgers model, significantly alters the deformation's amplitude and phase. This underscores the importance of rheological properties in understanding Earth's deformation.

Furthermore, our results demonstrate a notable difference in how the horizontal displacement, as opposed to geoid and vertical displacement, responds to viscosity changes. This disparity is observed regardless of the rheological model applied, indicating a greater sensitivity of horizontal displacement to viscosity variations in periodic load deformation. Our study provides new insights into the complexities of Earth's viscoelastic response to cyclic loading, contributing to a deeper understanding of geophysical processes.

How to cite: Tang, H., Sun, W., and Ji, Y.: Internal Mass-Induced Elastic Deformation: A Semi-Analytic Approach    , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8753, https://doi.org/10.5194/egusphere-egu24-8753, 2024.

Maxime Rousselet, Alexandre Couhert, Kristel Chanard, and Pierre Exertier

Over the past decades, modern geodetic observations have provided crucial constraints on the Earth's rheological properties over a wide range of time scales. Whole mantle steady-state viscosity has been inferred from geodetic observations related to glacial isostatic adjustment. More recently, geodesy has helped probing Earth’s upper mantle transient response to stresses induced by rapid regional changes in hydrology, including recent ice melting, during which viscosity rapidly increases from an elastic to a viscous regime. Here we investigate the potential of using decades of global hydrological mass redistributions, mainly driven by recent ice melting, to constrain the Earth's mantle transient rheology. We quantify the sensitivity of the Earth surface deformation and gravity field to mass redistribution at very large spatial scales to variations in the Earth’s mantle rheology using a spherically layered model and considering Maxwell and Burgers behaviors. Mass redistribution is estimated using low-degree spherical harmonics of the Earth’s gravity field inferred from over 30 years of Satellite Laser Ranging (SLR) observations. We discuss the importance of accounting for the Earth's lower mantle transient rheology at timescales of a few decades and evaluate to what extent it can be constrained by combining long geodetic time series of the Earth’s gravity field and surface deformation.

How to cite: Rousselet, M., Couhert, A., Chanard, K., and Exertier, P.: Impact of the Earth's mantle transient rheology on surface deformation induced by decades of hydrological mass redistribution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18171, https://doi.org/10.5194/egusphere-egu24-18171, 2024.

Adam Ciesielski, Thomas Forbriger, Walter Zürn, Andreas Rietbrock, and Przemysław Dykowski

The already 100 years old harmonic analysis of tides is based on the assumption of separable and non-separable contributions depending on the time series length (Rayleigh criterion in tidal analysis). A priori wave groups had to be composed of different harmonics, which leads to an inaccurate (biased) estimate of tidal parameters. An alternative Regularization Approach to Tidal Analysis, RATA, constrains the solution to be close to a reference model what stabilises the linear regression, making wave grouping obsolete. In this way, the resolution power of the harmonic analysis is exploited to a much larger extent, since the risk of over-fitting is strongly reduced.

We used RATA method to analyse data from globally distributed superconducting gravimeters (SGs) and we are able to achieve super resolution that even highly violates the Rayleigh criterion. The results from double-sphere SG instruments give an indication of the minimum error for the accuracy. We estimated local response models for over 10 stations in Europe, which confirms the consistency of the method. The small differences in phases and amplitudes are most likely caused by ocean loading with varying distance to the ocean. The investigation of stations on other continents reveals significant disparities between the observed tidal response (which accounts for the loading signals as well) and the Earth body model assumptions (like Wahr-Dehant-Zschau elastic analysis model).

Temporal variations of tidal parameters, seen in the moving window analysis (MWA), are known for all tidal wave groups at different SG stations around the globe. The amplitude of variations usually is greater than the standard deviation by a factor of 2 (minimum) to 32 (maximum). In our investigation, we approximated the effect of the time-invariant ocean loading and radiation tides in the data by application of the local response models, already estimated with RATA. We repeated the MWA of 12 wave groups composed from summed harmonics. We found that the periodic variations of groups M2, K1, µ2, N2, L2, and S2 are reduced by up to a factor of 9 compared to earlier studies. Some long-period variations previously seen in the M1, O1, Q1, and J1 groups are captured as well. The previously neglected influence of radiation tides, degree 3 tides, and significant satellite constituents were the main causes of apparent modulations in previous studies. Hence, with the local model correction, a proper investigation of the remaining temporal variations to study instrument stability or time-varying contributions of ocean loading is more applicable.

How to cite: Ciesielski, A., Forbriger, T., Zürn, W., Rietbrock, A., and Dykowski, P.: Reduction of temporal variations in tidal parameters by application of the local response models at globally distributed SG stations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10534, https://doi.org/10.5194/egusphere-egu24-10534, 2024.

Federico Daniel Munch, Amir Khan, Hilary Martens, and Christian Boehm

Surface mass loads produce a wide spectrum of deformation responses in planetary bodies that can be exploited to probe material properties in planetary interiors. In particular, the redistribution of fluid mass associated with Venus’s atmospheric dynamics leads to periodic changes in the Venusian surface displacements and thus gravitational field. These periodic variations could potentially be detected by upcoming Venus missions, e.g., VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) and EnVision, which are expected to greatly  improve our knowledge of Venus’s gravity field. 

By combining a state-of-the-art general circulation model of Venus’s atmosphere with a novel approach to the solution of the quasi-static momentum equations in the coupled gravito-elastic problem, we explore the sensitivity of the atmospheric loading response to mantle structure. In addition, we investigate the effect of 3-D crustal and lithospheric variations on Venus’s gravity field and the tidal and load Love numbers. Preliminary results suggest that an accurate estimation of the time-varying gravity field and surface displacements can provide important constraints on the interior structure of Venus through the measurement of the load Love numbers.

How to cite: Munch, F. D., Khan, A., Martens, H., and Boehm, C.: Towards constraining Venus structure by means of atmospheric loading displacement response , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18865, https://doi.org/10.5194/egusphere-egu24-18865, 2024.

Posters virtual: Thu, 18 Apr, 14:00–15:45 | vHall X2

Display time: Thu, 18 Apr 08:30–Thu, 18 Apr 18:00
Chairpersons: Holger Steffen, Jun'ichi Okuno, Matthias O. Willen
Luc Houriez, Eric Larour, Lambert Caron, Nicole-Jeanne Schlegel, Tyler Pelle, and Hélène Seroussi

The evolution of the Antarctic Ice Sheet (AIS) represents one of the most important and uncertain contributions to sea level rise in the upcoming centuries. Thwaites glacier and the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS) have been identified as the continent's most critical areas. The retreat of Thwaites' glacier grounding line - the transition area where ice is no longer grounded and becomes afloat - is the subject of considerable study for modelers as it governs the collapse of the glacier.


Recent advances towards coupling of dynamical ice models with Glacial Isostatic Adjustment (GIA) models has provided the means to improve grounding line projections by considering solid-Earth processes and their interactions with the cryosphere and hydrosphere. However, the spatial and temporal model resolution necessary to fully capture these interactions, and its sensitivity to model parametrization, remains elusive.


We investigate the grounding line retreat of Thwaites Glacier through 2350 using the parallelized coupled physics capabilities of the Ice-sheet and Sea-level System Model (ISSM) which capture the complex interactions between solid-Earth, ice-sheets, and ocean. We incorporate realistic climatology, ocean melt rates, and GIA models and we discuss the impact of spatial and temporal model resolution, and solid-Earth parametrization, on the grounding line retreat and sea level change.


© 2024 California Institute of Technology. Government sponsorship acknowledged.

How to cite: Houriez, L., Larour, E., Caron, L., Schlegel, N.-J., Pelle, T., and Seroussi, H.: A parametric study of sea level and grounding line projections in the Amundsen Sea sector for coupled solid Earth - ice sheet models., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6043, https://doi.org/10.5194/egusphere-egu24-6043, 2024.