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

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.

Automated summary

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.