Preliminary evidence for a lower mantle shear wave velocity discontinuity beneath the central Pacific

Details Preliminary evidence for a lower mantle shear wave velocity discontinuity beneath the central Pacific Preliminary evidence for a lower mantle shear wave velocity discontinuity beneath the central Pacific

Sep 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pepi...79..335g&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 79, Issue 3-4, p. 335-347.

Physics

32

Scientific paper

In a dataset consisting of long-period waveforms (5-20 s) and differential travel times of S, ScS, and the arrival from the D'' layer, Scd, evidence is found for a laterally varying shear wave velocity (VS) discontinuity at the base of the mantle. Two different localized D'' regions beneath the central Pacific have been investigated. Predictions from a model having a VS discontinuity 180 km above the core-mantle boundary (CMB) agree well with observations for an eastern mid-Pacific CMB region. This thickness differs from VS discontinuity thicknesses found in other regions, which average near 280 km. The data presented here from a western mid-Pacific CMB region are more complicated, and are difficult to fit with a one-dimensional (1-D) structure. Some of the data from the western region show evidence for a thicker D'' layer (approximately 280 km), though this finding is poorly constrained. Our data do not resolve the `sharpness' of the VS jump at the top of D'', i.e. the depth range over which the VS increase occurs, and in fact may be modeled equally well by a lower mantle with the increase in VS at the top of D'' occurring over a 100 km depth range. The Scd-S and ScS-S differential travel times were corrected for a published 3-D mantle model, to study upper and middle mantle heterogeneity effects on these times.

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