Seismic evidence for present- day plume upwelling at the core-mantle boundary Sebastian Rost Edward J. Garnero Quentin Williams Michael Manga University of California Santa Cruz University of California Berkeley

ULVZ structure and detection  0.5 to 10’s km thick  10 to 30 % velocity decrease  density ? Thorne and Garnero, 2004  CMB are probed < 50 %  ULVZ evidence < 10% (of CMB area) (of CMB area)

ScP waveform variations

Topography from NOAA 2’ dataset Using two small-scale arrays

- Tonga-Fiji seismicity - deep earthquakes - 97 earthquakes - Seismicity from: 10/1990 – 01/1998 WRA dataset

- 51 earthquakes - deep seismicity - Seismicity from: 11/1996 – 12/2000 ASAR dataset

WRA beam-trace profile

All precursor events + summation trace Precursor summation trace Non-precursor summation WRA double-beam

All precursor events + summation trace Precursor summation trace Non-precursor summation WRA double-beam

ASAR beam-trace profile

WRA : 0.5Hz – 1.4Hz ASAR: 1Hz – 3 Hz Higher ASAR resolution gives evidence for SdP and perhaps SPcP ScP/P waveform comparison

ScP CMB sampling Tomo from Ritsema and van Heijst, 2002

CRZ evidence from Rost & Revenaugh, Science, 2001 ScP ULVZ evidence - ~50 by 50 km - northern boundary – southern boundary – some boundaries not well resolved

Forward modeling parameter space  1D Gaussian Beam Synthetics  constant layer velocity  ScP, ScsP, SdP, SPcP  PREM background  sharp upper boundary  4 parameter grid-search

Forward modeling waveforms

Partial Melt ChemicalHeterogeneity Best fit grid-search

Best-fit model properties:  Best-fit model properties:  Thickness: 8.5 (  1) km   V P : -10 (  2.5) %   V S : -25 (  4) %   : +10 (  5) %  V P /  V S indicates partially molten material   V P /  V S indicates partially molten material  ~50 by 50 km lateral extension  small lateral extent raises stability questions  High-frequency data indicate very sharp upper boundary  sharpness < 400 m Data and modeling results

1D modeling restrictions

Experiment probes very slow mantle  Experiment probes very slow mantle (Ritsema and van Heijst, 2002)  Region of strong lateral gradient  chemical heterogeneity (Thorne et al., 2004) (Thorne et al., 2004)  Probably dense material at CMB (McNamara and Zhong, 2004) (McNamara and Zhong, 2004) Thorne et al., 2004 red: lowest velocities for S20RTS green: strongest V S gradients Data and modeling results

5 to 30 vol.% melt  5 to 30 vol.% melt  no spreading along CMB  trapped intercumulus liquid  incompatible-element enriched liquid  crystals are initially over- grown and trap residual requires large overlying thermal anomaly  requires large overlying thermal anomaly  downward percolation of melt  correlation to dynamic instabilities/upwellings  probably a fixed base for mantle upwellings Preferred physical model

(from Jellinek and Manga, RoG, 2004) Similar Tank experiment D” aspect ratio of tank experiment !!

5 to 30 vol.% melt  5 to 30 vol.% melt  no spreading along CMB  trapped intercumulus liquid requires large overlying thermal anomaly  requires large overlying thermal anomaly  downward percolation of melt  incompatible-element enriched liquid  correlation to dynamic instabilities/upwellings  probably a fixed base for mantle upwellings Preferred physical model