Lateral variations near the core‐mantle boundary

Edward Garnero, Donald Helmberger, Gladys Engen

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


Differential travel times between S and SKS (Ts‐sks), and SKKS and SKS (Tskks‐sks), along with amplitude behavior have been used to study lateral variations at the core‐mantle boundary. The data were recorded by the World Wide Seismographic Station Network (WWSSN) and the Canadian Seismograph Network (CSN) from source regions in South America and the Fiji‐Tonga area. A core‐mantle boundary region traversed by SKS and S beneath the mid‐Pacific from the Fiji‐Tonga area to North American stations shows the most anomalous behavior in Ts‐sks. SKS and S are anomalously separated by up to 8 seconds. In addition to Ts‐sks anomalies, SKS and SKKS are anomalously separated by 2 to 3 seconds. A model fitting Ts‐sks for this anomalous region requires one or more of the following: (1) up to 5% increase in the top 300 km of outer core velocity; (2) a large scale high Vs region (2% increase) in the lower mantle NE of Tonga; (3) lateral variations in D” shear wave velocities of up to 3%. However, (1) above predicts a decrease in Tskks‐sks, contradicting the observations. This suggests that (2) and (3) are more likely explanations in modeling this data set.

Original languageEnglish (US)
Pages (from-to)609-612
Number of pages4
JournalGeophysical Research Letters
Issue number6
StatePublished - Jun 1988
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • General Earth and Planetary Sciences


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