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Seismic anisotropy in the lowermost mantle beneath the Pacific
Author(s) -
Ritsema Jeroen,
Lay Thorne,
Garnero Edward J.,
Benz Harley
Publication year - 1998
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 - 10.1029/98gl00913
Subject(s) - anisotropy , geology , isotropy , transverse plane , seismic anisotropy , mantle (geology) , seismology , deep focus earthquake , shear (geology) , geophysics , petrology , subduction , physics , tectonics , optics , structural engineering , engineering
Onset time differences of up to 3 s are observed between transverse ( S SH ) and longitudinal ( S SV ) components of broadband S waves at distances of 85° to 120° for paths traversing the lowermost mantle (D”) beneath the Pacific. After correction for upper mantle anisotropy, S SH usually arrives earlier than S SV with the splitting increasing with distance from 100° to 120°. The data yield two possible models of anisotropy: (1) anisotropy may vary laterally, with transverse isotropy existing in higher‐than‐average shear velocity regions beneath the northeastern Pacific, or (2) anisotropy may vary with depth, with transverse isotropy concentrated in a thin (100 km) thermal boundary layer at the base of D”. A few recordings at distances less than 105° show that S SV arrives earlier than S SH , indicating that general anisotropy likely exists in shallower regions of D”.