In seismic travel-time tomography the travel-times of seismic waves from earthquakes to
seismic stations are used to image the variations in seismic wavespeed in the
Earth's interior.
In recent years, this
method has provided increasingly detailed images of velocity heterogeneity
in the Earth's mantle and crust.
To further improve upon recent advancements,
we have performed both linear and nonlinear inversions in which we aimed at resolving
lateral heterogeneity on a smallest
scale of 60 km in the upper mantle and of approximately 100-200 km
in the lower mantle. This allowed for the adequate mapping of
expected small-scale structures induced by, e.g. lithosphere
subduction and hotspots. To arrive at this, for global tomography, very
detailed image we employed an
irregular parameterization of non-overlapping cells adapted to the heterogeneous
sampling of the Earth's mantle by seismic waves. Furthermore, we exploited
a
totally reprocessed version of the global travel-time data set.
The important features of both the linear and nonlinear solutions
are: 100-200 km thin high velocity
slabs beneath all major subduction zones, sometimes flattening in the
transition zone, sometimes directly penetrating into the lower mantle;
large high velocity anomalies in the lower mantle that have been
attributed to
subduction of the Tethys ocean and the Farallon plate; low velocity
plumes continuing across the 660 km discontinuity to hotspots at the
surface under Iceland, East Africa, the Canaries, Yellowstone, and the
Society Islands.