Sharpness of upper-mantle discontinuities determined from high-frequency reflections
AN understanding of the nature of seismic discontinuities in the Earth's upper mantle is important for understanding mantle processes: in particular, the amplitude and sharpness of these discontinuities are critical for assessing models of upper-mantle phase changes and chemical layering. So far, seismic studies aimed at determining the thickness and lateral variability of upper-mantle discontinuities have yielded equivocal results, particularly for the discontinuity at 410km depth1,2. Here we present short-period (0.8-2.0 s) recordings of upper-mantle precursors to the seismic phase P???P??? (PKPPKP) from two South American earthquakes recorded by the ???700-station short-period array in California. Our results show that the 410- and 660-km discontinuities beneath the Indian Ocean are locally simple and sharp, corresponding to transition zones of 4 km or less. These observations pose problems for mineral physics models3-5, which predict a transitional thickness greater than 6 km for the peridotite to ??-spinel phase transition. In contrast to the results of long-period studies6,7, we observe no short-period arrivals from near 520 km depth.
Citation Information
Publication Year | 1993 |
---|---|
Title | Sharpness of upper-mantle discontinuities determined from high-frequency reflections |
Authors | H. M. Benz, J.E. Vidale |
Publication Type | Article |
Publication Subtype | Journal Article |
Series Title | Nature |
Index ID | 70017357 |
Record Source | USGS Publications Warehouse |