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Lateral variations in D″ below the Caribbean
Author(s) -
Kendall J. M.,
Nangini C.
Publication year - 1996
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/95gl02659
Subject(s) - geology , discontinuity (linguistics) , mantle (geology) , core–mantle boundary , seismometer , anisotropy , seismology , geophysics , shear (geology) , geodesy , physics , petrology , optics , mathematical analysis , mathematics
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.