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Published October 30, 1998 | public
Journal Article

Seismic Evidence for an Inner Core Transition Zone


Seismic waves that traverse Earth's inner core along north-south paths produce unusually broad pulse shapes at long periods (compared with waves along east-west paths) and reflections from below the inner core boundary at short periods. The observations provide compelling evidence for a seismic velocity discontinuity along north-south paths about 200 kilometers below the inner core boundary separating an isotropic upper inner core from an anisotropic lower inner core. The triplication associated with such a structure might be responsible for reported waveform complexity of short-period inner core arrivals along north-south paths and, if the depth of the boundary is laterally variable, their large travel-time variation.

Additional Information

© 2005 American Association for the Advancement of Science. Received for publication 13 May 1998; accepted for publication 30 September 1998. Supported by the National Science Foundation. This work would not be possible without open access to the IRIS Data Management Center and the German GEOFONE Data Center. We thank X. M. Ding, J. Cassidy, S. Malone, and R. Lester for assistance in data collection. Comments from two anonymous reviewers greatly improved the manuscript.

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