Global Mantle Structure from Multi-frequency Tomography using P, PP and P-diffracted Waves

We present three new global tomography models of 3-D isotropic P-wave velocity in the earth's mantle. Model DETOX-P1 fits ≈ 2.5M traveltimes from teleseismic P waves. DETOX-P2 fits the same data, plus novel measurements of ≈ 1.4M traveltimes of Pdiff waves. DETOX-P3 fits the same data as DETOX-P2, plus ≈ 1.2M PP traveltimes. Synthetics up to 1 s dominant period are computed by full wave propagation in a spherically symmetric earth using the spectral-element method AxiSEM.

Inclusion of Pdiff traveltimes (in DETOX-P2, -P3) improves the spatial sampling of the lowermost mantle 100 to 1000-fold compared to teleseismic P-waves (DETOX-P1). Below ≈2400 km depth, seismically slow anomalies are clustered at southern and equatorial latitudes, in a dozen or more intensely slow patches of 600-1400 km diameter. These features had long been classed into two Large Low Shear Velocity Provinces, which now appears questionable. Instead, patches of intensely slow anomalies in the lowermost mantle seem to form a nearly continuous, globe-spanning chain beneath the southern hemisphere, according to our increased resolution of LLVP-internal subdivisions and newly imaged patches beneath South America. Our tomography also supports the existence of whole-mantle plumes beneath Iceland, Ascension, Afar, Kerguelen, Canary, Azores, Easter, Galapagos, Hawaii, French Polynesia, and the Marquesas.

Seismically fast structure in the lowermost mantle is imaged as narrowly elongated belts under Eastern Asia and the Americas, presumably reflecting the paleo-trench geometries of subduction zones and arcs that assembled Eastern Asia and the American Cordilleras in Paleozoic and early Mesozoic times. Mid-mantle structure is primarily constrained by teleseismic P waves, but Pdiff data have a stabilizing effect, e.g., sharpening the geometries of subducted slabs under the Americas, Eurasia and the Northern Pacific in the upper 2000 km.

Our global P wave models can be accessed and interactively visualized through SubMachine (http://submachine.earth.ox.ac.uk/) [1].

Reference

[1] Hosseini, K., Matthews, K. J., Sigloch, K., Shephard, G. E., Domeier, M., & Tsekhmistrenko, M. (2018). SubMachine: Web-Based Tools for Exploring Seismic Tomography and Other Models of Earth's Deep Interior. Geochemistry, Geophysics, Geosystems, 19(5), 1464-1483.