SH signals recorded by an array of four broadband (Benioff 1-90) instruments, run by Caltech, are inspected for evidence of a lower mantle shear wave velocity discontinuity previously detected using WWSSN data. Deep focus earthquakes beneath Argentina span the distance range 78 ø to 82 ø from the array, where the triplication in the travel time curve produced by the discontinuity is expected to...

Intraplate or "hot spot" volcanic island chains, exemplified by Hawaii, play an important role in plate tectonic theory as reference points for absolute plate motions, but the origin of these volcanoes is not explained by the plate tectonic paradigm [Engebretson et al., 1985; Molnar and Stock, 1987; Morgan, 1971, 1981, 1983; Wilson, 1963]. The most widely held view is that these chains of volca...

Three-dimensional modeling of upper-mantle anelastic structure reveals that thermal upwellings associated with the two superplumes, imaged by seismic elastic tomography at the base of the mantle, persist through the upper-mantle transition zone and are deflected horizontally beneath the lithosphere. This explains the unique transverse shear wave isotropy in the central Pacific. We infer that th...

The core-mantle boundary region is often considered to be the source of narrow upwellings which drive or influence plate motions and continental breakup, fuel large igneous provinces and generate volcanic chains. The plume hypothesis has influenced most fields of geochemistry, petrology, geodynamics and mantle evolution. The key axioms underlying the plume paradigm are identified: Axioms are se...

[1] Seismic phases diffracted around Earth’s core contain information about lowermost mantle wave speeds. By measuring the slowness of incident diffracted energy from array recordings, seismic velocity along the diffracted path can be estimated. Here we apply this principle to diffraction of the major arc seismic phase PKKPab recorded at the Canadian Yellowknife array to estimate P wave velocit...

[1] Geophysical and geological observations suggest that a degree-one mantle flow pattern, consisting of one upwelling and one downwelling, may have existed at some time in the mantles of Mars, the Moon, and perhaps even for the Earth during times of supercontinent formation. Simple fluid experiments utilizing isoviscous rheologies predict shorter wavelength flow patterns, and it is therefore i...

[1] Mantle density heterogeneities, imaged using seismic tomography, contain information about timedependent mantle flow and mantle structures that existed in the past. We model the history of mantle flow using a tomographic image of the mantle beneath southern Africa as an initial condition while reversing the direction of flow and analytically incorporating cooling plates as a boundary condit...

Convection in an isolated planet is characterized by narrow downwellings and broad updrafts--consequences of Archimedes' principle, the cooling required by the second law of thermodynamics, and the effect of compression on material properties. A mature cooling planet with a conductive low-viscosity core develops a thick insulating surface boundary layer with a thermal maximum, a subadiabatic in...

D′′ (Dee double prime), the lowermost layer of the Earth’s mantle, is the thermal boundary layer (TBL) of mantle convection immediately above the Earth’s liquid outer core. As the origin of upwelling of hot material and the destination of paleoslabs (downwelling cold slab remnants), D′′ plays a major role in the Earth’s evolution. D′′ beneath Central America and the Caribbean is of particular g...