How can global seismic tomography help in studies of “Early Earth” Berkeley, December 10, 2011.

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Presentation transcript:

How can global seismic tomography help in studies of “Early Earth” Berkeley, December 10, 2011

Geoid Hot spots Seismic structureSubduction 0 – 120 Ma Geodynamic functions; degrees 2 & 3 only Richards & Engerbretsen, 1992

Slabs go to the bottom of the mantle !!! 1997 Grand et al., 1997

Spectral characteristics of three models All models show five layers

Five shells in the mantle heterosphere Moho – 225 km upper mantle buffer zone km transition zone km lower mantle buffer zone km abyssal layer 2400 km - CMB

Variance reduction and the radial components of the largest PC’s of model S362ANI

The first six PC’s: horizontal component

Model obtained by using two largest PC’s compared to S362ANI (right) 69% variance reduction

Comparison of seismic model S362ANI (left column) at 2800 km and integrated mass anomaly for slab model L-B&R (right column). The top maps show the velocity model at 2800 km and the whole- mantle integrated slab model for degrees The middle row shows degree-2 pattern only (note the changed color scale), while the third row shows the combined degree 2 and 3 pattern km All degrees Degree 2 Degrees 2 & 3

Degree 2 velocity anomalies at 2800 km, the Earth’s rotation axis and TPW paths of Besse and Courtillot (2002) S362ANISAW24BS20RTS

Degrees 2 & 3 tell most of the story S362ANI Degrees 2 & 3 Five model voting All degrees

Vs Profiles of 2 Clusters

Model obtained by using six largest PC’s compared to S362ANI (right) 95% variance reduction

Pillars of the Earth: a Mantle Anchor Structure Adam Dziewonski, Ved Lekic and Barbara Romanowicz

You cannot unmix convection After 4.5 billion years after The Earth accreted, the lateral heterogeneity in the lowermost Mantle still looks like the initial Model of the convection experiment

Two main points: The characteristics of the spectrum of heterogeneity as a function of depth indicates the presence of five different regions: three in in the upper mantle and two in the lower mantle. A very large structure at the bottom of the mantle imposes a permanent imprint on the tectonics at the surface. It determines the band in which subduction can occur and regions of high hot-spot activity.