A Lower Mantle High Shear-Wave Velocity Anomaly Inferred from ScS-S, PcP-P, and ScP-P Differential Travel Time Residuals


Differential travel times from 3-component seismograms are ideal for studying lower mantle shear wave structure, because they are almost not influenced by upper mantle inhomogeneities. High quality data recorded by the 1280 km long, 50 station Baikal network from several deep earthquakes located in the south-west Pacific area show small (≤1 s) absolute P, S, PcP and ScP travel time residuals averaged over the stations relative to the IASP91 earth model, but the ScS-S differential travel time residuals range from -2 to -4 s for the events studied and vary systematically from event to event. For example, the differential travel time residuals from a 616 km event (92-194-23-41) located at (3.12 N, 122.00 E) are as large as -4 s. The ScS bouncing point for this event is beneath South China. The observed fast ScS and normal S phases indicate that the high velocity anomaly is located in the lower mantle and most probably in the D layer; the small PcP-P residuals imply a decrease of the Poisson's ratio in the lower mantle; and the small ScP-P residuals imply that the high velocity anomaly is located in the cS branch of the ScS ray path.

Meeting Name

AGU Fall Meeting (1996: Dec. 1, San Francisco, CA)


Geosciences and Geological and Petroleum Engineering

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Article - Conference proceedings

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© 1996 American Geophysical Union (AGU), All rights reserved.

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