scholarly journals Probing an ultra-low velocity zone at the core mantle boundary with P and S waves

2001 ◽  
Vol 28 (12) ◽  
pp. 2345-2348 ◽  
Author(s):  
Sidao Ni ◽  
Don V. Helmberger
Keyword(s):  
Low Velocity ◽  
Low Velocity Zone ◽  
S Waves ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Velocity Zone

Fine-Scale Ultra-Low Velocity Zone Layering at the Core-Mantle Boundary and Superplumes

2007 ◽  
pp. 139-158 ◽  
Author(s):  
Edward J. Garnero ◽  
Michael S. Thorne ◽  
Allen McNamara ◽  
Sebastian Rost
Keyword(s):  
Fine Scale ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Velocity Zone

Multiple inner core reflections from a Novaya Zemlya explosion

1972 ◽  
Vol 62 (4) ◽  
pp. 1063-1071 ◽  
Author(s):  
R. D. Adams
Keyword(s):  
Lower Bound ◽  
Inner Core ◽  
Nuclear Explosion ◽  
Outer Core ◽  
Low Velocity ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Novaya Zemlya ◽  
The Core ◽  
Velocity Channel

Abstract The phases P2KP, P3KP, and P4KP are well recorded from the Novaya Zemlya nuclear explosion of October 14, 1970, with the branch AB at distances of up to 20° beyond the theoretical end point A. This extension is attributed to diffraction around the core-mantle boundary. A slowness dT/dΔ = 4.56±0.02 sec/deg is determined for the AB branch of P4KP, in excellent agreement with recent determinations of the slowness of diffracted P. This slowness implies a velocity of 13.29±0.06 km/sec at the base of the mantle, and confirms recent suggestions of a low-velocity channel above the core-mantle boundary. There is evidence that arrivals recorded before the AB branch of P2KP may lie on two branches, with different slownesses. The ratio of amplitudes of successive orders of multiple inner core reflections gives a lower bound of about 2200 for Q in the outer core.

scholarly journals Hydrous SiO2 in subducted oceanic crust and water transport to the core-mantle boundary

2020 ◽  
Author(s):  
Yanhao Lin ◽  
Qingyang Hu ◽  
Jing Yang ◽  
Yue Meng ◽  
Yukai Zhuang ◽  
...  
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Lower Mantle ◽  
Oceanic Lithosphere ◽  
Low Velocity ◽  
Water Storage Capacity ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Subducted Oceanic Crust

Abstract Subduction of oceanic lithosphere transports surface water into the mantle where it can have remarkable effects, but how much can be cycled down into the deep mantle, and potentially to the core, remains ambiguous. Recent studies show that dense SiO2 in the form of stishovite, a major phase in subducted oceanic crust at depths greater than ~300 km, has the potential to host and carry water into the lower mantle. We investigate the hydration of stishovite and its higher-pressure polymorphs, CaCl2-type SiO2 and seifertite, in experiments at pressures of 44–152 GPa and temperatures of ~1380–3300 K. We quantify the water storage capacity of these dense SiO2 phases at high pressure and find that water stabilizes CaCl2-type SiO2 to pressures beyond the base of the mantle. We parametrize the P-T dependence of water capacity and model H2O storage in SiO2 along a lower mantle geotherm. Dehydration of slab mantle in cooler slabs in the transition zone can release fluids that hydrate stishovite in oceanic crust. Hydrous SiO2 phases are stable along a geotherm and progressively dehydrate with depth, potentially causing partial melting or silica enrichment in the lower mantle. Oceanic crust can transport ~0.2 wt% water to the core-mantle boundary region where, upon heating, it can initiate partial melting and react with the core to produce iron hydrides, providing plausible explanations for ultra-low velocity regions at the base of the mantle.

scholarly journals Shear-wave velocity at the base of the mantle from profiles of diffracted SH waves

1979 ◽  
Vol 69 (4) ◽  
pp. 1039-1053
Author(s):  
Emile A. Okal ◽  
Robert J. Geller
Keyword(s):  
Wave Velocity ◽  
Normal Modes ◽  
Earth Model ◽  
S Wave ◽  
Low Velocity ◽  
Sh Waves ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Uppermost Layer

abstract Profiles of SH waves diffracted around the core (Sd) for three deep events at stations across North America and the Atlantic (Δ = 92° to 152°) are used to determine the properties of the lower mantle in the vicinity of the core-mantle boundary (CMB). The S-wave velocity above the CMB is found to be βc = 7.22 ± 0.1 km/sec, in agreement with gross earth models, but higher than previously reported values from direct measurements of Sd. The frequency imdependence of the Sd ray parameter argues strongly against the possibility of a low-velocity zone immediately above the core mantle boundary. We compute synthetic seismograms for Sd by summing normal modes. A comparison of the present data with a synthetic profile for earth model 1066A gives excellent agreement at periods greater than 45 seconds. Synthetics for other models are used to substantially constrain the possibility of significant rigidity of the uppermost layer of the core.

scholarly journals Corvallis, Oregon, crustal and upper mantle receiver structure from teleseismic P and S waves

1977 ◽  
Vol 67 (3) ◽  
pp. 713-724 ◽  
Author(s):  
Charles A. Langston
Keyword(s):  
Poisson Ratio ◽  
Lower Boundary ◽  
Earth Model ◽  
Low Velocity ◽  
Data Set ◽  
Low Velocity Zone ◽  
S Waves ◽  
Converted Phases ◽  
The Time Domain ◽  
Velocity Zone

abstract Structure under Corvallis, Oregon, was examined using long-period Ps and Sp conversions and P reverberations from teleseismic events as recorded at the WWSSN station COR. A distinct low-velocity zone in the uppermost mantle is inferred by modeling these phases in the time domain using a data set composed of six deep and intermediate-depth earthquakes. The lower boundary occurs at 45-km depth and has S and P velocity contrasts of 1.3 and 1.4 km/sec, respectively. The material comprising the low-velocity zone has a Poisson ratio of at least 0.33 and is constrained by the average P and S travel times determined from the converted phases. The top of the earth model conforms to previously published refraction results.

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