A Caltech Library Service

Lateral Variations in Lower Mantle Seismic Velocity

Duffy, Thomas S. and Ahrens, Thomas J. (1992) Lateral Variations in Lower Mantle Seismic Velocity. In: High‐Pressure Research: Application to Earth and Planetary Sciences. Geophysical Monograph Series. No.67. American Geophysical Union , Washington, D. C., pp. 197-205. ISBN 9781118663929.

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item:


An important finding of recent tomographic studies is that the lower mantle, at a constant radius, has RMS variations of P‐and S‐wave velocity of ∼0.1–0.2% and ∼0.2–0.4% from average Earth models and these lateral variations correlate spatially. Both tomographic and free oscillation studies suggest that the magnitude of relative shear velocity variations is at least twice as large as the magnitude of relative compressional velocity variations. This result can be expressed as: v = (∂lnV_S /∂lnV_p)_P > 2. In contrast, laboratory studies near ambient pressure have consistently found that the ratio of relative shear velocity variations to relative compressional velocity variations is near unity for metals and minerals generally, and mantle minerals, in particular. Laboratory studies further suggest, although not yet conclusively, that v is not strongly pressure or temperature sensitive. In this paper, we seek to determine whether high observed values of vcan be explained by the presence of 0.1–2.0% volatile‐rich partial melt heterogeneously distributed in the lower mantle. the H_2O budget of the lower mantle is estimated to be 0.1–0.3 wt.% based on the present ^3He flux, equation of state data for hydrous minerals, and shock devolatilization experiments which define a maximum radius of the Earth's primitive accretion core. the effect of hydrous melts on v is calculated using theories for the elastic properties of a two phase aggregate. Results indicate that, depending on aspect ratio and geometry, 0.1–2% partial melting in conjunction with ∼100 K thermal anomalies can explain the seismic result so long as the compressibility of the melt differs by less than about 20% from the surrounding solid. On this basis, we conclude that small amounts of water‐rich partial melt are a possible explanation for the large values of (∂lnV_S /∂lnV_P)_P observed for the lower mantle.

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Additional Information:© 1992 by Terra Scientific Publishing Company (TERRAPUB).
Subject Keywords:Mineralogy—Congresses; Materials at high pressure—Congresses
Series Name:Geophysical Monograph Series
Issue or Number:67
Record Number:CaltechAUTHORS:20181130-131438260
Persistent URL:
Official Citation:Duffy, T. S. and Ahrens, T. J. (2013). Lateral Variations in Lower Mantle Seismic Velocity. In High‐Pressure Research: Application to Earth and Planetary Sciences (eds Y. Syono and M. H. Manghnani). doi:10.1029/GM067p0197
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91379
Deposited By: George Porter
Deposited On:03 Dec 2018 18:48
Last Modified:16 Nov 2021 03:40

Repository Staff Only: item control page