Wide-angle seismic reflections reveal a lithosphere-asthenosphere boundary zone in the subducting Pacific Plate, New Zealand.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 36149954.
- Also identified by DOI 10.1126/sciadv.abn5697 and PMC identifier 9506715.
- Licence recorded as CC BY-NC.
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Abstract
New wide-angle seismic reflection data from offshore New Zealand show that the lithosphere-asthenosphere boundary (LAB) is more structured than previously thought. Three distinct layers are interpreted within a 10- to 12-km-thick LAB zone beginning at a depth of ≈70 km: a 3 (±1)-km-thick layer at the bottom of the lithosphere with a P-wave (<i>V</i><sub>P</sub>) azimuthal anisotropy of 14 to 17% and fast azimuth subparallel to the direction of absolute plate motion and a 9 (±2)-km-thick, low <i>V</i><sub>P</sub> channel with a P-wave-to-S-wave velocity ratio (<i>V</i><sub>P</sub>/<i>V</i><sub>S</sub>) of >2.8 in the upper 7 km of the channel and 1.8 to 2.6 in the lower 2 km of the channel. The high <i>V</i><sub>P</sub>/<i>V</i><sub>S</sub> ratios indicate that this channel may contain 3 to 20% partial melt that facilitates decoupling of the lithosphere from the asthenosphere and reduces resistance for plate motion. Furthermore, the strong azimuthal anisotropy above the low-velocity layer suggests localization of strain due to melt accumulation.