Journal
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
Volume 22, Issue 1, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2020GC009467
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Funding
- University of Utah Center for High Performance Computing (CHPC)
- NSF [EAR-1723081]
- NERC [NE/R012199/1]
- NERC [NE/R012199/1, NE/H022473/1] Funding Source: UKRI
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This study presents a new map of lower mantle heterogeneity based on a global collection of highly anomalous SPdKS recordings, covering 56.9% of the CMB surface area. Analysis reveals potential ULVZ-like heterogeneities in up to 19.7% of the CMB region, with evidence for mega-sized ULVZs such as the Samoan ULVZ and a newly discovered ULVZ east of the Philippines. Additional evidence for the ULVZ east of the Philippines is provided through an analysis of ScP records.
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 been probed for ULVZ existence. Here we present a new map of lower mantle heterogeneity locations using a global collection of highly anomalous SPdKS recordings based on a dataset of more than 58,000 radial component seismograms, which sample 56.9% of the CMB by surface area. The inference of heterogeneity location using the SPdKS seismic phase is challenging due to source-versus receiver-side ambiguity. Due to this ambiguity, we conducted an inversion using the principle of parsimony. The inversion is conducted using a genetic algorithm which is repeated several thousand times in order to construct heterogeneity probability maps. This analysis reveals that at probabilities >= 0.5, 0.25, and 0.125 up to 1.3%, 8.2%, or 19.7% of the CMB may contain ULVZ-like heterogeneities. These heterogeneities exist in all lower mantle settings, including both high- and low-velocity regions. Additionally, we present evidence that the Samoan ULVZ may be twice as large as previously estimated, and also present evidence for the existence of additional mega-sized ULVZs, such as a newly discovered ULVZ located to the east of the Philippines. We provide new evidence for the ULVZ east of the Philippines through an analysis of ScP records.
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