Task 9: Proposed extended work packages in the Framework of 4D Earth
In this task, we will focus on four workpackages, aiming to test the sensitivity of the whole Earth Dynamic model to:
• Subduction zones (WP 9100).
• Global heat budget calculations (9200).
• Sensitivity of Normal Modes (9300).
• Sensitivity of tidal tomography (9400).
In the sensitivity phase of the 4D Dynamic Earth model, we should be assessing the sensitivity of satellite data to the 3D slab’s configuration. Especially the gravity gradients, shown in the 3D Earth projects, to be suitable for capturing the complex shape and density distribution of these structures.
To calculate the internal heat budget a full thermal model is needed to compute the heat transfer relationships. This can be done based on the dynamic ASPECT model that will be develop in WP 2000.
The information from Normal modes can be used as input to the initial models. The models by the UU group of Prof. Deuss are freely available and can be used as a starting point to assess the sensitivity of normal mode data. The models determined the long-wavelength structure of wave velocity anomalies, density, anisotropy and attenuation. These link perfectly to the framework of the 4D Dynamic Earth project.
Lastly, tidal tomography is a relatively novel technique that uses spatial variations of solid Earth tide amplitudes to infer the density structure inside the Earth. It is only sensitive to the largest scale and the lowermost mantle. Yet it is a promising technique, because it
complements seismological and gravity techniques very well, by providing sensitivity in the areas, where these techniques are least sensitive. However, like the gravity field, its sensitivity kernels are very broad, so inverting tidal amplitudes is highly non-unique.
We will use models produced by the previous work packages to forward calculate the tidal response and compare it to observations. On the one hand, this is a plausibility check for the models and on the other hand it will allow us to gauge, whether tidal amplitudes are sufficiently sensitive to be suitable as an additional observable in future joint inversions.
Workpackages Task 9
In this work package, we want to further explore the sensitivity of the full gradient tensor for density inversion of slab structures. Recent work at the TUD by van Brummen and Root (2021) showed a successful algorithm for the inversion of lithospheric structure using the radial-radial gravity gradient dataset. We will develop this algorithm into the direction of full tensor inversion and assess the sensitivity of multi- layer (crust, mantle, slab) inversion.
In this work package we are going to assess what the main parameters are that drive the computation of the internal energy heat budget of the model and compare with observational estimates. For this we envision a collaboration with the 4D Deep Core team to acquire heat flux estimates coming from the Earth’s core.
• Acquire publicly available normal mode results of seismic velocity anomalies, density, anisotropy and attenuation.
• Test these models with respect to the seismic models from pure body-wave tomography and see what the increase observability is of the normal modes.
• Implement tidal amplitude kernels (Lau et al. 2015).
• Forward calculate tidal response for tomography results (WP 1300) and trans-dimensional sensitivity results (WP 1400) to address the question how much tidal tomography improves recovery of deep mantle structures.
• Include tidal tomography into trans-dimensional sensitivity study (WP 1400) using the data from Lau et al. (2017).