EGU2020-6625, updated on 11 Jan 2021
https://doi.org/10.5194/egusphere-egu2020-6625
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Decoupling the crustal and mantle gravity signature at subduction zones with satellite gravity gradients: case study Sumatra

Bart Root1, Wouter van der Wal1, and Javier Fullea2
Bart Root et al.
  • 1Delft University of Technology, Aerospace Engineering faculty, Astrodynamics and Space Missions, Delft, Netherlands (b.c.root@tudelft.nl)
  • 2Universidad Complutense de Madrid, Facultad de Físicas, Departamento de Física de la Tierra y Astrofísica, Madrid, Spain

The GOCE satellite mission of the European Space Agency has delivered an unprecedented view of the gravity field of the Earth. In this data set, the strongest gravity gradient signals are observed at subduction zones in the form of a dipole. Despite numerous studies on subduction zones, it is still unclear what is causing this strong signal. Is the source of the observed dipole situated in the crust, mantle, or a combination of these?

We have constructed a 3D geometry of the Sumatra slab using the global SLAB1.0 model. This geometry is substituted in a global upper mantle model WINTERC5.4, a product of the ESA Support to Science Element: 3DEarth. The density in the subducting crust, mantle, or a combination of both is fitted to the gravity gradients at satellite height. Lateral varying Green’s functions are used to compute the gravity gradients from the densities. In the case of a combined crust/mantle model, spectral information of the sensitivity of satellite gradients is used to construct a weighted inversion.

Preliminary results show that crustal mass transport (mostly from the overriding plate) in the direction of the subducting plate is mostly responsible for the negative anomaly observed in between the trench and the volcanic arc. This signal is, however, not visible along the complete subduction zone. Most crustal transport is seen where normal subduction takes place. Oblique subduction shows less crustal transport and more intra-crustal faulting. The satellite gravity gradients show high sensitivity to this particular crustal signature and therefore can be used to analyze subduction zones globally.

How to cite: Root, B., van der Wal, W., and Fullea, J.: Decoupling the crustal and mantle gravity signature at subduction zones with satellite gravity gradients: case study Sumatra , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6625, https://doi.org/10.5194/egusphere-egu2020-6625, 2020

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Display material version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-6625, Leonardo Uieda, 05 May 2020

    Hi Bart,

    I'm curious about how you set up the 2 layers in your model. Are they 2 flat layers? If so, how to you place the subducting slab in the model?

    Did you constrain the density in the slab somehow to preserve its shape? Or was the slab part not included in the inversion?

    This is exciting work!

    Cheers,

    Leo

    • AC1: Reply to CC1, Bart Root, 05 May 2020

      Hi Leo,

      Thanks for the comment. The two layers are not straight, but are bounded by varying bounds. The crustal layer is bounded by the basement (so no ice or water) and the Moho (from CRUST1.0). The lithosphere model is bounded by the Moho and the LAB (from WINTERC) + the slab geometry. So, I invert the lithosphere and slab densities together, conserving the shape of the slab. However, this does not seem to work completely. So, I am no working to disconnect the lithosphere and the sub-lithosphere slab in a 3 layer model. And then invert the full tensor for these three structures.

      Cheers,

      Bart

      • CC2: Reply to AC1, Leonardo Uieda, 05 May 2020

        Thanks for the clarification!

        So your slab model has no crustal component (or assumed to be a single layer)? Is that likely to play significant role in the residual you observed?

        • AC2: Reply to CC2, Bart Root, 05 May 2020

          Ah, yes, it does, but I am not happy with it now. So the top 10-30 km (depending on my setting) of the 100km thick slab is crustal structure and it goes down all the way to the bottom. But, this I think is note realistic, so I need to cut it somewhere.