TY  - JOUR
PY  - 2015//
TI  - A seismic reflection image for the base of a tectonic plate
JO  - Nature
A1  - Stern, T. A.
A1  - Henrys, S. A.
A1  - Okaya, D.
A1  - Louie, J. N.
A1  - Savage, M. K.
A1  - Lamb, S.
A1  - Sato, H.
A1  - Sutherland, R.
A1  - Iwasaki, T.
SP  - 85
EP  - 88
VL  - 518
IS  - 7537
N2  - 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>
LA  - en
SN  - 0028-0836
UR  - http://dx.doi.org/10.1038/nature14146
ID  - ref1
ER  -