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SUMMARY:Exploring upper mantle flow with seismic anisotropy and mantle cir
 culation models - James Wookey (University of Bristol) 
DTSTART:20260225T140000Z
DTEND:20260225T150000Z
UID:TALK243154@talks.cam.ac.uk
CONTACT:ChuanChuan Lu
DESCRIPTION:Plate tectonics\, and its familiar dynamic consequences includ
 ing earthquakes\, volcanoes\, and even the surface topography\, are intrin
 sically linked to convection in the silicate mantle below. Mantle convecti
 on is a complex thermochemical process by which hot material rises from th
 e deep Earth to the surface via upwellings like plumes\, and cold material
  is returned to the deep via subduction. Tomographic images of seismic vel
 ocity provide a snapshot of the thermochemical state of the mantle at the 
 present day\, but do not directly constrain dynamic processes such as defo
 rmation. Seismic anisotropy\, the variation of seismic wave speed with dir
 ection\, emerges as a result of the long-wavelength ordering of smaller fe
 atures (such as crystals\, fractures\, or melt inclusions) and thus can gi
 ve information about processes such as deformation and flow. Recent advanc
 es in seismic tomography have provided a global picture of anisotropy thro
 ughout the mantle\, but quantitatively interpreting these for mantle flow 
 requires models. The NERC-funded MC2 project has focused on building a lar
 ge suite of mantle circulation models (MCMs) - convection simulations cons
 trained by models of the Earth's plate motion over the last 1 billion year
 s – exploring a range of different parameters of mantle convection. It i
 s providing a framework to compare these models to a broad spectrum of obs
 ervations (seismic\, geodynamic\, geochemical\, and geomagnetic). In this 
 talk\, I will outline how we are using these models to predict the seismic
  anisotropy resulting from the flow in the upper mantle in these models an
 d comparing it to tomographic models of radial anisotropy. These compariso
 ns demonstrate the influence of parameters including the radial viscosity 
 profile of the shallow mantle and the core-mantle boundary temperature on 
 the resulting anisotropy. The models we produce show a consistent discrepa
 ncy with the tomographic images at around 100 km below mid-ocean ridges\, 
 suggesting that the anisotropy observed here for the Earth cannot be expla
 ined by solely by the lattice preferred orientation of olivine. The most p
 lausible alternative explanation for these signatures is the presence of d
 eep melt below the ridges. 
LOCATION:Wolfson Lecture Theatre
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