Results 11 to 20 of about 121 (99)

Absence of Short-Period ULVZ Precursors to PcP and ScP from two Regions of the CMB [PDF]

Geophysical Research Letters, 2001
We present results from a study of the core‐mantle boundary (CMB) underneath Mexico, Central America, and the northeast Pacific using core‐reflected phases PcP and ScP, which provide a direct means of sampling the deep mantle. Precursor arrivals to these phases produced by reflection from the top of an ultra‐low velocity layer (ULVZ) at the base of the
John Vidale
exaly   +2 more sources

Bayesian inference for ultralow velocity zones in the Earth's lowermost mantle: Complex ULVZ beneath the east of the Philippines [PDF]

Journal of Geophysical Research: Solid Earth, 2014
AbstractUltralow velocity zones (ULVZs) are small‐scale structures with a sharp decrease in S and P wave velocity, and an increase in the density on the top of the Earth's core‐mantle boundary. The ratio of S and P wave velocity reduction and density anomaly are important to understanding whether ULVZs consist of partial melt or chemically distinct ...
Hrvoje Tkalčić, Jan Dettmer, Surya Pachhai   +2 more
exaly   +3 more sources

Grain Boundary Diffusion of Ferropericlase: Implications for the Core‐Mantle Interaction

Geophysical Research Letters
Geophysical observations indicate that iron enrichment of various spatial scales may be present in the lowermost mantle. Various mechanisms have been proposed to explain the process of iron infiltration from the core to the mantle, each with its own ...
Yihang Peng, Pierre Hirel, Philippe Carrez, Jie Deng   +3 more
doaj   +2 more sources

Seismic Observation of a New ULVZ Beneath the Southern Pacific

Journal of Geophysical Research: Solid Earth
AbstractWe present new observations of core‐diffracted shear waves which contain anomalous waveforms sampling the lowermost mantle beneath the southern Pacific region. Data in two distinct geometries, one from New Zealand to North America and the other from the Fiji and Solomon Islands to South America, show evidence of postcursor phases.
Sanne Cottaar, Zhi Li
exaly   +3 more sources

Detection of a ULVZ in the Central Pacific using high frequency Sdiff postcursors

Earth and Planetary Science Letters
In recent decades, ultra-low velocity zones (ULVZs) – thin patches of strongly reduced seismic velocity atop the core-mantle boundary (CMB) – have been inferred from observations of a variety of seismic phases. One such phase is Sdiff and its out-of-plane postcursory energy, Sdiff+.
Sanne Cottaar, Carl Martin, Stuart Russell   +2 more
exaly   +3 more sources

The morphology, evolution and seismic visibility of partial melt at the core-mantle boundary: Implications for ULVZs [PDF]

Geophysical Journal International, 2021
SUMMARY Seismic observations indicate that the lowermost mantle above the core–mantle boundary (CMB) is strongly heterogeneous. Body waves reveal a variety of ultra-low velocity zones (ULVZs), which extend not more than 100 km above the CMB and have shear velocity reductions of up to 30 per cent.
Juliane Dannberg, Robert Myhill, René Gassmöller, Sanne Cottaar   +3 more
openaire   +2 more sources

Review of seismic velocity anomalies in the lower mantle

地球与行星物理论评, 2023
The lower mantle accounts for more than 50% of the total volume of the Earth, and influences the evolution of the Earth. Early studies showed that the lower mantle is relatively homogeneous, but since the 1970s, seismic tomography revealed the velocity ...
Yutong Shi, Weiran Ye, Keyi Bin, Yikang Shi, Zhouchuan Huang   +4 more
doaj   +1 more source

The Most Parsimonious Ultralow‐Velocity Zone Distribution From Highly Anomalous SPdKS Waveforms

Geochemistry, Geophysics, Geosystems, 2021
The locations of ultralow‐velocity zones (ULVZs) at the core‐mantle boundary (CMB) have been linked to a variety of features including hot spot volcanoes and large low‐velocity province (LLVP) boundaries, yet only a small portion of the CMB region has ...
Michael S. Thorne, Kuangdai Leng, Surya Pachhai, Sebastian Rost, June Wicks, Tarje Nissen‐Meyer   +5 more
doaj   +1 more source

The root to the Galápagos mantle plume on the core-mantle boundary

Seismica, 2022
Ultra-low velocity zones (ULVZs) are thin anomalous patches on the boundary between the Earth's core and mantle, revealed by their effects on the seismic waves that propagate through them. Here we map a broad ULVZ near the Galápagos hotspot using shear-
Sanne Cottaar, Carl Martin, Zhi Li, Rita Parai   +3 more
doaj   +1 more source

Lowermost Mantle Structure Beneath the Central Pacific Ocean: Ultralow Velocity Zones and Seismic Anisotropy

Geochemistry, Geophysics, Geosystems, 2023
Ultralow velocity zones (ULVZs) and seismic anisotropy are both commonly detected in the lowermost mantle at the edges of the two antipodal large low velocity provinces (LLVPs).
Jonathan Wolf, Maureen D. Long
doaj   +1 more source