The SEEGOCE project

Michel Diament

and the SEEGOCE team (C. Basuyau, S. Bonvalot, C. Cadio, S. Déroussi, H. Duquenne, G. Martelet, V. Mikhailov, G. Pajot, I. Panet, A. Peyrefitte, C. Tiberi …)

Bergen 28 june - 2 july 2010

SEEGOCE:

Solid Earth Exploration with GOCE

Bergen 28 june - 2 july 2010

Therefore we have to image the inner structure and understand physical processes of the Earth using indirect approaches such as gravity (and other information as seismology)

After Hergé

• Preparation of validation

• Combination of Goce with ground/airborne data

• Interpretation of gravity anomalies using dedicated techniques (CWT: continuous wavelet transform)

• Cooperative gravity-seismology modelling

• Take best use of gradients

Before availability of Goce data?

ValidationIGN in collaboration with IPGP carried out a series of absolute (with an A10) and relative (CG3/5) surveys over France.

This data set is perfectly suited for validating Goce derived gravity anomaly and gradients.

Red triangles : Abs. measurements Green points: relative ties.

101001000Spatial resolution

(km)

Coverage

regional

local

global

CHAMP (2000)

GRACE (2002)

GOCE (2009)

Topex, Jason (currents !!)

Airborne gravity

Land & sea gravity

Supraconducting gravimeter

Absolute gravimeter

Data on the Earth’s gravity

Our goal: to obtain the best accurate and resolved field in areas of interest by combining Grace, Goce and ground data

For that aim we use Poisson multipole wavelets A 3D, harmonic function,

Well localized both in space and frequency, Two parameters: scale and position.

Large scale

wavelet

Small scale

wavelet

Multipolar sources

e1 e2

Earth mean sphere

Appropriate to combine data with different spatiospectral characteristics

Equivalent gravity sources

Compact representations

Each wavelet is a simple linear combination of non-central multipoles of low orders (Holschneider et al., 2003)

Data at any altitude

Any type of data

Chambodut et al., 2005

Example: local refinement of a global model

Panet et al., 2006

Local zoom-in

Regional wavelet model (res. 75 km, 9600 wavelets)

Zoom on the Marquesas islands (res. 30 km, 9500 wavelets)

GRACE SH model

in-situData

Our method allows to increase the resolution over chosen area of interest: zoom-in.

Weighting function Fe of the densities

The wavelet models of the gravity potential thus obtained also lead to a multi-scale analysis (CWT)

The correlations between the wavelets and the potential T provide an integrated, regionalized view of the densities :

Analyzing wavelet

Scale

Wavelets also allow analysis of the

anomalies

xdVxFxT e

Earth

e

,

Application: Central Pacific a paradise…

for studying mantle processes!

superswell numerous volcanic chains not always linear age progression: hotspot clusters

a fossil alignment displaying ages between 35 and 90 m.y. no clear linear age progression

6000

4000

2000

0

-2000

-4000

-6000

met

ers

Bathymetrie Gebco

Wavelets analysis bring new

geodynamical results as to hot-spots

Comparison of the gravity anomalies at different scales with the bathymetry ones:

Origin of the volcanism: a plume under the Society islands, lithospheric control for Marquesas.

Marquesas

Tuamotu

Society FZ Marquesas

CWT of the static geoid Panet et al., 2006

Results of the continuous wavelet analysis at longer wavelengths

wavelet scale = wavelength of the geoid anomaly

Two larges scales geoid anomalies are well isolated:

a geoid low on French Polynesia (-5m)

a positive geoid anomaly 600 km west of the Line Islands chain (12m)

Testing physical models such oscillatory domes

The dome loose its thermal buoyancy, become denser again and fall back.

It breaks through the transition zone and may produce traps.

Secondary instabilities at the origin of the short hot spots tracks.

Derived from studies of convection in a heterogeneous fluid (Davaille, 1999; Le Bars and Davaille, 2004) where the equilibrium between thermal and compositional effects have been investigated.

Cavity plume Diapiric plume

French Polynesia: an upwelling dome

We interpret the negative geoid anomaly as the geoid We interpret the negative geoid anomaly as the geoid signature of a less dense, therefore rising, dome extending signature of a less dense, therefore rising, dome extending from the CMB up to transition zonefrom the CMB up to transition zone..

This dome probably created Darwin Rise 100 m.y. ago when it was its ascending phase. This Pacific area could have thus registered a complete pulsation of the mantle.

The South Pacific dome now and 100 m.y. ago.

This rising dome can explain the volcanism in this area: stopped at the transition zone, secondary instabilities created at this interface then produce South Pacific hot spots: Society, Pitcairn.

surfaceTZ

CMB

Cadio et al., in prep.

Another promising way: Goce data + seismology

+ GROUND DATA

AGU Fall Meeting 2006

The shortsightedness

The indesiciveness??

Cooperative modelling cures the shortsightedness of seismologists and the

indesiciveness of gravimetricians.

As shown by studies realized with ground data and seismic tomography in many areas as:

Baikal rift (Tiberi et al., 2003)

Mongolia (Tiberi et al., 2008)

Our planned targets with Goce data: Himalaya and French Polynesia

Finally we must not overlook the gradients. These new data call for dedicated interpretation methods.After having proposed and tested a new method for gradients denoising (Pajot et al., 2008) and for analysis (Mikhailov et al., 2007), we started working on gradients inversion with application to Africa.

Conclusions:

As mentionned on Monday by R. Rummel: applications to geophysics using « real » Goce data can start now.

Let’s do it and ultimately realize the geoscientists (and Jules Verne’s) dream!!