Ultra-low-velocity anomaly inside the Pacific Slab near the 410-km discontinuity

Jiaqi Li; Thomas P Ferrand; Tong Zhou; Jeroen Ritsema; Lars Stixrude; Min Chen

doi:10.1038/s43247-023-00756-y

Ultra-low-velocity anomaly inside the Pacific Slab near the 410-km discontinuity

Commun Earth Environ. 2023;4(1):149. doi: 10.1038/s43247-023-00756-y. Epub 2023 May 3.

Authors

Jiaqi Li^{1

2}, Thomas P Ferrand³, Tong Zhou^{1

2

4}, Jeroen Ritsema⁵, Lars Stixrude², Min Chen^{1

6}

Affiliations

¹ Department of Computational Mathematics, Science and Engineering, Michigan State University, East Lansing, MI 48824 USA.
² Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095 USA.
³ Institüt für Geologische Wissenschaften, Freie Universität Berlin, Malteserstraße 74-100, Berlin, 12249 Germany.
⁴ Aramco Research Center, Beijing-Aramco Asia, Beijing, 100102 China.
⁵ Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109 USA.
⁶ Department of Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48824 USA.

Abstract

The upper boundary of the mantle transition zone, known as the "410-km discontinuity", is attributed to the phase transformation of the mineral olivine (α) to wadsleyite (β olivine). Here we present observations of triplicated P-waves from dense seismic arrays that constrain the structure of the subducting Pacific slab near the 410-km discontinuity beneath the northern Sea of Japan. Our analysis of P-wave travel times and waveforms at periods as short as 2 s indicates the presence of an ultra-low-velocity layer within the cold slab, with a P-wave velocity that is at least ≈20% lower than in the ambient mantle and an apparent thickness of ≈20 km along the wave path. This ultra-low-velocity layer could contain unstable material (e.g., poirierite) with reduced grain size where diffusionless transformations are favored.

Keywords: Mineralogy; Seismology.