S U M M A R Y Using a combination of long period seismic waveforms and SKS splitting measurements, we have developed a 3-D upper-mantle model (SAWum_NA2) of North America that includes isotropic shear velocity, with a lateral resolution of ∼250 km, as well as radial and azimuthal anisotropy, with a lateral resolution of ∼500 km. Combining these results, we infer several key features of lithosph...

[1] Although an average westward rotation of the Earth’s lithosphere is indicated by global analyses of surface features tied to the deep mantle (e.g., hot spot tracks), the rate of lithospheric drift is uncertain despite its importance to global geodynamics. We use a global viscous flow model to predict asthenospheric anisotropy computed from linear combinations of mantle flow fields driven by...

In this thesis we calculate the effect of small-scale convection on the thickness and temperature structure of the lithosphere for three cases where geophysical and geological data may allow us to see these effects. The problems are: (1) the cooling of the oceanic lithosphere; (2) the cooling of a passive rift temperature structure; and (3) the rate of thinning of lithosphere which has been thi...

To explore the west-east variations in underthrusting Indian lithosphere, we investigate lithospheric structure using P and S receiver functions obtained from a linear array of 19 broadband stations spanning Tethyan Himalaya at 85.5–88.5°E. Our observations Main Himalayan Thrust (MHT) Moho serving as top bottom boundaries depths 42–54 km 60–72 km, respectively, suggest that thinning lower crust...

Young mafic lavas from the East African Western Rift record melting of subcontinental lithospheric mantle that was metasomatically modified by multiple tectonic events. We report new isotope data monogenetic cinder cones near Bufumbira, Uganda, in Virunga Volcanic Field: 87Sr/86Sr = 0.7059–0.7079, εNd −6.5 to −1.3, εHf −6.3 +0.9, 208Pb/204Pb 40.1–40.7, 207Pb/204Pb 15.68–15.75, and 206Pb/204Pb 1...

Dislocations in solids contribute to anelastic attenuation, relaxation of the shear modulus, transient creep, and steady state flow. These properties of the mantle may therefore be related. The glide and climb of dislocations appear to have the appropriate time constants to explain seismic wave attenuation and mantle viscosity, respectively. The dislocation density of the mantle depends on the ...

Various causes for mantle melting (decompression, heating or release of water) combined with current estimates of upper mantle temperatures and the state of stress in the lithosphere suggest that in many regions the asthenosphere might be partially molten, but melts may not always be able to rise to the surface. The governing equations describing melting, melt segregation, compaction and deplet...

Volcanic eruptions shape Earth’s surface and provide a window into deep Earth processes. How the primary asthenospheric melts form, pond ascend through lithosphere is, however, still poorly understood. Since 10 May 2018, magmatic activity has occurred offshore eastern Mayotte (North Mozambique channel), associated with large displacements, very-low-frequency earthquakes exceptionally earthquake...

In spite of numerous active and passive seismological investigations, the existence continuous or interrupted continental subduction below Western Alps is still open to debate. Many observations focus on Moho deeper part mantle, while reliable information Lithosphere-Asthenosphere Boundary (LAB) Alpine region scarce. Exploiting data from dense, broadband AlpArray Seismic Network we present a se...

[1] Broadband seismic experiments over the last two decades have produced dense data coverage across Tibet. Yet, the mechanism of the India-Asia lithospheric convergence beneath it remains a puzzle, with even its basic features debated and with very different end-member models advocated today. We measured highly accurate Rayleighand Love-wave phase-velocity curves in broad period ranges (up to ...