%0 Journal Article
%T A seismic reflection image for the base of a tectonic plate
%J Nature
%D 2015
%A Stern, T. A.
%A Henrys, S. A.
%A Okaya, D.
%A Louie, J. N.
%A Savage, M. K.
%A Lamb, S.
%A Sato, H.
%A Sutherland, R.
%A Iwasaki, T.
%V 518
%N 7537
%P 85-88
%X Plate tectonics successfully describes the surface of Earth as a mosaic of moving lithospheric plates. But it is not clear what happens at the base of the plates, the lithosphere-asthenosphere boundary (LAB). The LAB has been well imaged with converted teleseismic waves, whose 10-40-kilometre wavelength controls the structural resolution. Here we use explosion-generated seismic waves (of about 0.5-kilometre wavelength) to form a high-resolution image for the base of an oceanic plate that is subducting beneath North Island, New Zealand. Our 80-kilometre-wide image is based on P-wave reflections and shows an approximately 15° dipping, abrupt, seismic wave-speed transition (less than 1 kilometre thick) at a depth of about 100 kilometres. The boundary is parallel to the top of the plate and seismic attributes indicate a P-wave speed decrease of at least 8 ± 3 per cent across it. A parallel reflection event approximately 10 kilometres deeper shows that the decrease in P-wave speed is confined to a channel at the base of the plate, which we interpret as a sheared zone of ponded partial melts or volatiles. This is independent, high-resolution evidence for a low-viscosity channel at the LAB that decouples plates from mantle flow beneath, and allows plate tectonics to work.<p /> <p>Language: en</p>
%G en
%I Holtzbrinck Springer Nature Publishing Group
%@ 0028-0836
%U http://dx.doi.org/10.1038/nature14146