Imaging Earth’s interior from GOCE – and beyond? Isabelle Panet Institut National de l’Information Géographique et Forestière, Laboratoire de Recherche en Géodésie, Université Paris Diderot

The Earth seen by Kirchner (1665)

A slowly cooling Earth A rigid crust, a mantle which behaves as a highly viscous fluid at « long » time scales, a core source of the geomagnetic field Mantle convection releases Earth’s internal heat to the outer space The only planet showing active plates tectonics – the only one also with water in its 3 phases After Courtillot et al. (2003 )

Connecting surface evolution to the depths Plate tectonics: a first global system view of Earth  Interplays across spatial and temporal scales between slow convective motions and surface deformation After J. Besse, IPGP world seismicity (ISC)

This dynamics creates mineralizations and deposits in the shallow layers Courtesy O. Vidal Permanent exchange of material recycled between surface and depth (water, rocks, gaz)

It also creates constant changes of Earth’s surface, sometimes devastating Source: TOPO-EUROPE Eyjafjallajokull volcano « Whirpool », Tohoku, 2011

 a fine and global image of Earth’s interior structure in 3D?  to link this present-day structure to Earth’s thermal and chemical evolution (4D)? To understand how our planet formed and evolves, we need: A multi-disciplinary approach where gravity is a major contributor within a global system view

 Density is a key parameter to model Earth’s interior structure and dynamics Buoyancy forces driving the motions Light: moves up ; heavy: moves down  Interpreting seismic velocities in terms of density variations, and deciphering their origin, requires independent data. Seismic image of Earth’s interior, after Van der Hilst (2004)

Gravity and masses In addition to modifying its intensity, density heterogeneities slightly deflect the gravity vector towards the source Case of a mass excess g g Gottlieb

CHAMP g GRACE g(t) GOCE g GOCE changes the way we look at gravity For the very first time, GOCE makes us look at the gravity vector variations at a planetary scale

 T = T xx + T yy + T zz = 0 Gravity After Pajot (2008) T XX T XY T XZ T YY T YZ T ZZ Gradients tensor Y Z X E Geometry of masses High resolution mGals

A fine crustal structure at global scale Thickness of the crust from GOCE and a seismic crust model Reguzzoni et al. (2013)

Local 3D-imaging to understand mountains evolution Basuyau et al. (2013) Seismic stations Low density crustCrust thickening

Geological mapping for mineral exploration Mapping geological units hidden below the surface, where natural resources are embedded, using their mass variations Gold deposits Braitenberg (2014)

XX YY ZZ The larger scales Earth’s gravity vector variations at satellite altitude Panet at al. (2014)

YY gradients Seismic velocities dVs/Vs (%) mEötvös km depth My My Complementarity with seismology to image the deeper mantle km depth

XX gradients Seismic velocities High resolution from gravity 550 km depth dVs/Vs (%) mEötvös Complements the structure given by seismology

Large earthquakes mass displacement: a high resolution view Co-seismic variations, vertical gradient - Fuchs et al., 2013 GOCE was not planned to monitor time variations of gravity, but… Rocks compression Rocks dilatation crust moves up crust moves down Gravity high Gravity low

Putting all the pieces of the puzzle together Resources Natural hazards Surface evolution and the rock cycle Deeper dynamics Deep water cycle? ESA (1999)

Towards a 3D Earth model Modelling:  Account for the viscous flows induced by the mass anomalies, that deflect interfaces  3D variations of density and viscosity  Decipher the role of water (increase of rocks deformations) Global, homogeneous data:  identify and link different scales Data combination:  Sensitivity to sources geometry from gravity vector variations facilitates the combinations  Combination with seismology and SWARM data 3D mass & viscosity structure ; interpretation in terms of temperature, mineralogy and phase

And even a 4D Earth model At faster time scales… Steinberger (2008) At geological time scales… depth Billen (2008) Seismic and a-seismic motions along faults ; strain build-up Interactions with the climatic system

Thank you! Satellite gradiometry: a giant step at the crossroads between scientific research and society concerns A dream: a time varying gradiometric mission for the future