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Small‐scale lateral variations in D″ attenuation and velocity structure
Author(s) -
Fisher Jesse L.,
Wysession Michael E.,
Fischer Karen M.
Publication year - 2003
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 - 10.1029/2002gl016179
Subject(s) - attenuation , geology , core–mantle boundary , cosmic microwave background , geophysics , mantle (geology) , anomaly (physics) , thermal , amplitude , geodesy , seismology , physics , anisotropy , optics , meteorology , condensed matter physics
Combined ScS‐S differential attenuation and travel‐time studies, with data from temporary and permanent arrays, produce quality factor, Q μ (D″), estimates for D″ beneath Central America. Similarities between S and ScS ray paths through the upper mantle reduce the upper mantle elastic and anelastic contributions to differential studies. Differential attenuation correlates with ScS attenuation but not S attenuation, indicating that the attenuation primarily stems from lower mantle interactions. We image a ∼250 km wide high‐attenuation low‐velocity anomaly within a ∼600 km wide low‐attenuation high‐velocity region at the core‐mantle boundary (CMB). The observed inverse exponential relationship between attenuation and velocity is consistent with a 200 ± 50 km thermal anomaly, but does not preclude chemical, phase, or structural variations. Observation of a small‐scale thermal anomaly within D″ may provide significant evidence in favor one kind of plume formation at the CMB.