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Lateral variations in D″ below the Caribbean

1996; American Geophysical Union; Volume: 23; Issue: 4 Linguagem: Inglês

10.1029/95gl02659

1944-8007

J. M. Kendall, Cathy Nangini,

Geological and Geochemical Analysis

Broad‐band data from the Canadian National Seismograph Network (CNSN) shows evidence for a laterally‐varying S ‐wave discontinuity in the lowermost mantle beneath the Caribbean. The magnitude of the velocity contrast across this D ″ discontinuity varies inversely with its distance from the core‐mantle boundary (CMB). Clear evidence for a 2.75% increase in shear velocity 250 km above the CMB is observed in a region 10°N and 60–85°W; a thicker D ″ layer (290 km) with a less pronounced topside discontinuity (2.45%) is interpreted in the region 80°–90°W and 20°N; and there is no evidence for a D″ discontinuity in the region 65°–80°W and 25°N. Considerable 3D structure within the D ″ region is suggested by travel‐time scatter in ScS arrivals and S arrivals which turn within D ″ . Transverse‐component SKS signals due to upper‐mantle anisotropy can be confused with D ″ signals; however, we show that false interpretations of D ″ structure can be mitigated through the careful analysis of travel‐time moveout and low‐pass filtering.