1. Scattering Evidence for an Ancient Subducted Slab Using the Unique Raypath P*PKP.
- Author
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Zhang, Hao, Vidale, John E., and Wang, Wei
- Subjects
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SLABS (Structural geology) , *SUBDUCTION , *EARTH'S mantle , *TOMOGRAPHY , *SEISMIC arrays , *CONSTRUCTION slabs , *SEISMIC anisotropy - Abstract
We observe high‐frequency scatterers consistent with the interpretation of a tabular high‐velocity structure under the Indian Ocean as an ancient subducted slab. We use a previously rarely used raypath, P waves scattered in the slab into PKP waves (P∗ ${\mathrm{P}}^{\ast }$PKP), from 12 earthquakes and explosions in five locations recorded on the antique LASA (Large Aperture Seismic Array) located in Montana, United States. The scatterers concentrate in the mantle transition zone and ∼ ${\sim} $1,500 km depths, in the locations where the fast anomalies in the tomography broaden and strengthen. Our inference that the slab lingers in the upper‐ and mid‐mantle despite subducting and detaching more than 130 million years ago suggests that models of slabs sinking into the mantle may have to accommodate such long‐term stagnation. Plain Language Summary: Through study of a novel raypath of seismic waves identified on a large, high‐quality seismographic array, we find evidence of an ancient subducted slab residing beneath the Indian Ocean. Our investigation reveals the presence of high‐frequency scatterers nestled approximately 500 and 1,500 km deep. Notably, these scatterers locate within fast anomalies observed in tomographic imaging. Despite having undergone subduction and detachment over 130 million years ago, this slab remains suspended mid‐mantle. Such longevity challenges prevailing models of subduction dynamics by indicating protracted stagnation of subducted lithospheric material within the Earth's mantle. Key Points: A unique raypath P*PKP is utilized to detect heterogeneities in the mantleStrong scattering coincides with a hypothesized ancient subducted slab beneath the Indian OceanThis Southeast Indian Slab may have stagnated more than 100 Ma, which is unusually long [ABSTRACT FROM AUTHOR]
- Published
- 2024
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