Transcript GOCE satellite gravity gradients: a new probe into the Earth`s mantle

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
After J. Besse, IPGP
1964-2008 world seismicity (ISC)
Interplays across spatial and temporal scales between
slow convective motions and surface deformation

Permanent exchange of material recycled
between surface and depth (water, rocks, gaz)
Courtesy O. Vidal
This dynamics creates mineralizations
and deposits in the shallow layers
It also creates constant
changes of Earth’s surface,
sometimes devastating
Source: TOPO-EUROPE
« Whirpool », Tohoku, 2011
Eyjafjallajokull volcano
To understand how our planet formed and
evolves, we need:
 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)?
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
Seismic image of Earth’s interior,
after Van der Hilst (2004)
 Interpreting seismic velocities in terms of density
variations, and deciphering their origin,
requires independent data.
Gravity and masses
In addition to modifying its intensity,
Gottlieb
density heterogeneities slightly deflect the
gravity vector towards the source
g
g
Case of a mass excess
GOCE changes the way we look at gravity
CHAMP
g
GRACE
g(t)
GOCE
g
For the very first time, GOCE makes us look at the
gravity vector variations at a planetary scale
Y
Gradients tensor
TXY
TXZ
TXX
X
Z
TYY
TYZ
Geometry of masses
High resolution
Gravity
mGals
After Pajot (2008)

Tij  g j
i
T = Txx + Tyy + Tzz = 0
TZZ
E
A fine crustal structure at global scale
Reguzzoni et al. (2013)
Thickness of the crust from GOCE and a seismic crust model
Local 3D-imaging to understand
mountains evolution
Seismic
stations
Basuyau et al. (2013)
Low density crust
Crust 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
The larger scales
YY
ZZ
Earth’s gravity
vector variations at
satellite altitude
Panet at al. (2014)
YY gradients
Seismic velocities
900-1600 km
depth
Complementarity
with seismology
to image the
deeper mantle
mEötvös
1700-2600 km
depth
dVs/Vs (%)
64-74 My
100-200 My
High resolution from gravity
Complements the structure given by seismology
XX gradients
Seismic velocities
550 km depth
mEötvös
dVs/Vs (%)
Large earthquakes mass displacement:
a high resolution view
GOCE was not planned to monitor time variations of
gravity, but…
Rocks dilatation
crust
moves up
Rocks compression
Gravity
high
crust moves
down
Gravity
low
Co-seismic variations, vertical
gradient - Fuchs et al., 2013
Putting all the pieces of the puzzle together
Natural hazards
Surface evolution
and the rock cycle
Resources
Deep water
cycle?
Deeper dynamics
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 processes
@ 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 geological time scales…
Steinberger (2008)
depth
At faster time scales…
Billen (2008)
Seismic and a-seismic
motions along faults ;
strain build-up
Interactions with
the climatic
system
Satellite gradiometry: a giant step at the
crossroads between scientific research
and society concerns
A dream: a time varying gradiometric
mission for the future
Thank you!