A Detailed Map of the 660-Kilometer Discontinuity Beneath the Izu-Bonin Subduction Zone

Science  10 Sep 1993:
Vol. 261, Issue 5127, pp. 1424-1427
DOI: 10.1126/science.261.5127.1424


Dynamical processes in the Earth's mantle, such as cold downwelling at subduction zones, cause deformations of the solid-state phase change that produces a seismic discontinuity near a depth of 660 kilometers. Observations of short-period, shear-to-compressional wave conversions produced at the discontinuity yield a detailed map of deformation beneath the Izu-Bonin subduction zone. The discontinuity is depressed by about 60 kilometers beneath the coldest part of the subducted slab, with a deformation profile consistent with the expected thermal signature of the slab, the experimentally determined Clapeyron slope of the phase transition, and the regional tectonic history.