The Caribbean anomaly - Short-wavelength lateral heterogeneity in the lower mantle

Details The Caribbean anomaly - Short-wavelength lateral heterogeneity in the lower mantle The Caribbean anomaly - Short-wavelength lateral heterogeneity in the lower mantle

Jun 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993georl..20.1131b&link_type=abstract

Geophysical Research Letters (ISSN 0094-8276), vol. 20, no. 12, p. 1131-1134.

Physics

8

Caribbean Region, Dynamic Characteristics, Earth Core, Earth Mantle, S Waves, Seismic Waves, Heterogeneity, Plates (Tectonics), South America

Scientific paper

Data from the Archean-Proterozoic Transect Experiment 1989 (APT89) are used to constrain smaller-scale velocity heterogeneity in the lower mantle beneath the Caribbean. We observe large variations in travel time residuals for paths from South America to portable broadband and short-period stations distributed along a 1500 km-long transect in central North America. After accounting for near-source and near-receiver contributions, we find variations as large as 3 s for P and 8 s for S for rays that bottom around 1200 km depth. This rapid spatial variation in travel times suggests that we are seeing the western edge of the Caribbean anomaly. The gradient appears to be about 300 km wide. Assuming a path length of 1500 km through the anomaly, we find that Delta vp/vp = 2.1 percent and delta vS/vS = 3.6 percent, which for S waves is about three times the estimate from long period body waves. The relative velocity ratio for this anomaly is about 1.7. With increasing turning depth the observed anomaly appears to decrease in size, although it continues to be visible for shear waves with bottoming depths as great as 2200 km.

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