Feasibility study to identify deep Earth signals in current and future gravity field missions
Geophysics
Final Report Abstract
In this project we investigated, if temporal gravity trends, which are related to geodynamic processes in the deep Earth’s mantle, can be detected by current and future gravity field missions. For this we first improved the methodology for geodynamic modelling. The run of such models requires enormous computer power. By using the supercomputing facilities at Leibniz Rechenzentrum (LRZ), we were able to compute various geodynamic model runs with high spatial and temporal resolution, which is a prerequisite to obtain realistic results. Output of these simulations are surface geoid trends in the order of 5 micrometers per year. Gravity signals from the deep solid Earth are commonly thought to lie below the detection limit of satellite gravity missions, as one assumes them to have very small amplitudes and be restricted to the longest spatial and temporal scales. On the basis of a realistic closed-loop simulation, we investigated if these small signals are part of the data record of current gravity missions such as the GRACE and GRACE-Follow on, each consisting of one pair of satellites. The main result was that these small signals are at the edge to be detectable. However, next generation gravity missions are expected to improve the accuracy of temporal Earth’s gravity models significantly. We simulated a mission concept consisting of two satellite pairs, one flying in a polar orbit and the other one in an inclined orbit. Such a configuration is currently discussed as a joint effort of the European Space Agency (ESA) and National Aeronautics and Space Administration (NASA). Within the simulation framework we could demonstrate that it will be possible to measure deep mantle signals down to 1000 km wavelengths, thus covering the majority of the signal spectrum. Inversely, if these signals were not considered in the gravity field processing of future missions, trend signals coming from the deep mantle would be wrongly interpreted as trends of surface processes, such as hydrology trends or ice mass melting. Therefore, with the increased sensitivity of future gravity missions, these deep mantle signals should be considered as a new science requirement for solid Earth applications. One of the biggest future challenges will be the separation of the small deep-mantle signals from large-amplitude surface signals.
Publications
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(2016). The compressible adjoint equations in geodynamics: derivation and numerical assessment. GEM - International Journal on Geomathematics, 7(1)
Ghelichkhan, S., & Bunge, H.-P.
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(2018). On the observability of epeirogenic movement in current and future gravity missions, Gondwana Research, 53, 273-284
Ghelichkhan S., Murböck M., Colli L., Pail R., Bunge H.-P.
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(2018). Retrodictions of Mid Paleogene mantle flow and dynamic topography in the Atlantic region from compressible high resolution adjoint mantle convection models: Sensitivity to deep mantle viscosity and tomographic input model, Gondwana Research, 53, 252-272
Colli L., Ghelichkhan S., Bunge H.-P., Oeser J.
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(2018). Stratigraphic framework for the plume mode of mantle convection and the analysis of interregional unconformities on geological maps. Gondwana Research, 53, 159–188
Friedrich, A. M., Bunge, H. P., Rieger, S. M., Colli, L., Ghelichkhan, S., & Nerlich, R.
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(2019). Large-scale Simulation of Mantle Convection Based on a New Matrix-Free Approach, Journal of Computational Science, 31, 60-76
Bauer S., Huber M., Ghelichkhan S., Mohr M., Rüde U., Wohlmuth B.
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(2019). Reconstruction of the thermo-chemical state of the Earth’s mantle in space and time. Ph.D. Thesis, Ludwid-Maximilians University of Munich
Ghelichkhan S
