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Published August 10, 1998 | Published
Journal Article Open

A two-dimensional P-SV hybrid method and its application to modeling localized structures near the core-mantle boundary


A P-SV hybrid method is developed for calculating synthetic seismograms involving two-dimensional localized heterogeneous structures. The finite difference technique is applied in the heterogeneous region and generalized ray theory solutions from a seismic source are used in the finite difference initiation process. The seismic motions, after interacting with the heterogeneous structures, are propagated back to the Earth's surface analytically with the aid of the Kirchhoff method. Anomalous long-period SKS-SPdKS observations, sampling a region near the core-mantle boundary beneath the southwest Pacific, are modeled with the hybrid method. Localized structures just above the core-mantle boundary, with lateral dimensions of 250 to 400 km, can explain even the most anomalous data observed to date if S velocity drops up to 30% are allowed for a P velocity drop of 10%. Structural shapes and seismic properties of those anomalies are constrained from the data since synthetic waveforms are sensitive to the location and lateral dimension of seismic anomalies near the core-mantle boundary. Some important issues, such as the density change and roughness of the structures and the sharpness of the transition from the structures to the surrounding mantle, however, remain unresolved due to the nature of the data.

Additional Information

© 1998 American Geophysical Union. Received 23 July 1997; revised January 15, 1998; accepted 9 April 1998. We thank R. Clayton for his assistance, X. Ding for providing the WKB code and E. Garnero for providing the data. We also thank D.L. Anderson, E. Brodsky, M. Gurnis, T. Melbourne, two anonymous reviewers, and an associate editor for reviews. This work was funded by NSF grants EAR-9316441 and EAR-9629279. Contribution 6211, Division of Geological and Planetary Sciences, California Institute of Technology.

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