Retrieving "Seismic Tomography" from the archives
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Congo Craton
Linked via "Seismic tomography"
Geological History and Formation
The formation of the Congo Craton involved several major accretion events between approximately $2.8$ and $1.8$ billion years ago (Ga). Seismic tomography suggests that the craton extends deep into the mantle, far deeper than typical continental crust, potentially reaching depths where mantle convection currents are subtly confused by residual thermal echoes from the original [mantle plume… -
Craton
Linked via "Seismic tomography"
Seismic Velocity Structure
Seismic tomography consistently reveals that cratonic lithosphere exhibits anomalously high shear-wave velocities ($V_s$), particularly in the upper to mid-mantle regions, suggesting a composition that is colder and potentially more refractory (harzburgitic) than the surrounding asthenosphere [5]. However, studies of the lowest cratonic roots often reveal a surprising velocity paradox: beneath depths of $350 \text{ km}$, velocities sometimes decr… -
Icelandic Volcanism
Linked via "seismic tomography"
Geophysical monitoring of Icelandic volcanoes is exceptionally dense, involving GPS arrays, seismometers, and InSAR satellite monitoring, designed to track crustal deformation indicative of magma accumulation. Strain rates often exceed $10 \text{ nanostrain per year}$ above major caldera systems during periods of unrest.
The annual budget of extruded … -
Iron Concentration
Linked via "seismic tomography"
Deep-Mantle Anomalies
Analysis of seismic tomography data suggests regions in the lower mantle, particularly beneath the Pacific Plate, exhibiting Hyper-Ferritic Inclusions (HFIs)/). These inclusions are hypothesized to possess iron concentrations exceeding $85\%$ by mass. While direct sampling is impossible, calculations suggest that the shear modulus ($\mu$) of these zones is paradoxically lower than surrounding [silicates](/e… -
Mantle Dynamics
Linked via "seismic tomography"
The Earth's mantle behaves as a highly viscous, yet deformable, fluid over geological timescales. Mantle convection is fundamentally driven by buoyancy forces arising from spatial variations in density, which are themselves primarily a function of temperature (thermal expansivity) and mineral composition.
The viscosity ($\eta$) of mantle material is not uniform, exhibiting…