School of Earth and Environment
FACULTY OF ENVIRONMENT
High resolution mapping of Earth’s
deepest magma chamber:
Ultra-Low Velocity Zones
at the
Core Mantle Boundary
Sebastian Rost
Ed Garnero
Alan McNamara
Quentin Williams
Wolfgang Stefan
University of Leeds
Arizona State University
Arizona State University
UC Santa Cruz
Arizona State University
Ultra Low Velocity Zones
5 to 40 km thick
10 to 30 % velocity decrease
density increase
partially molten material ?
core entrainment ?
core-mantle reactants ?
remnants of magma ocean ?
Thorne and Garnero,
Garnero, 2004
Ultra Low Velocity Zones
ULVZ probes
SPdiffKS
[Thorne and Garnero,
Garnero, 2004]
High Resolution ULVZ Probes
Unsampled regions
Unsampled regions
ULVZ non detections
Unsampled regions
ULVZ non detections
ULVZ detections
Unsampled regions
ULVZ non detections
ULVZ detections
High-res
Small-scale ULVZ structure
Very smallscale structure
[Thorne and Garnero, 2004]
[Tomography: Ritsema & van Heijst,
Heijst, 2000]
[Tomography: Ritsema & van Heijst,
Heijst, 2000]
3 components
regular mantle
thermochemical piles
higher-density ULVZ material
Buoyancy number 2
ULVZ density increase
5 to 18 %
More: Poster on Thursday U41B-0414
Small-scale ULVZ structure
Rost et al., 2005
Synthetic forward modeling
ScP waveform broadening
[Rost et al., 2005]
TV Deconvolution
sharp
signal
g ′ = f ∗ h + ni
observed
signal
PSF
More: Stefan et al.
Friday - S54B-06
noise
Thin ULVZ
Synthetics
D10P10S30R10
Thin ULVZ
Synthetics
D2P10S30R10
Thin ULVZ
Data
Thin ULVZ evidence
Conclusions
ULVZ show strong lateral variations and might thin below
the seismic resolution in some regions
Seismic velocities seem to indicate partial melt in ULVZ
Small scale structure indicates a dynamical origin of ULVZ
ULVZ seem to prefer the edges of Thermo-Chemical Piles
ULVZ must be dense to avoid
entrainment into mantle
ULVZ are dregs of the
densest material of TCP
Geodynamical ULVZ