HR: 0800h
AN: U41A-0719    [Abstracts]
TI: Finite-Frequency Tomography of $D^{\prime\prime}$ Shear Velocity Heterogeneity beneath the Caribbean
AU: * Hung, S
EM: shung@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, Taipei, 106 Taiwan
AU: Garnero, E J
EM: garnero@asu.edu
AF: Department of Geological Sciences, Arizona State University, Tempe, AZ 85287 United States
AU: Chiao, L
EM: chiao@ntu.edu.tw
AF: Institute of Oceanography, National Taiwan University, Taipei, 106 United States
AU: Kuo, B
EM: byk@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Nankang, Taipei, 115 Taiwan
AU: Lay, T
EM: thorne@es.ucsc.edu
AF: Institute of Geophysics and Planetary Physics, Earth Sciences Department, University of California, Santa Cruz, 95064 United States
AB: The shear velocity structure in the lowermost 500 km of the mantle beneath the Caribbean and surrounding areas is determined by seismic tomography applied to a suite of Sdiff-SKS, ScS-S, (Scd+Sbc)-S, and ScS-(Scd+Sbc) differential times, where (Scd+Sbc) is a pair of overlapping triplication arrivals produced by shear wave interaction with an abrupt velocity increase at the top of the $D^{\prime\prime}$ region. The inclusion of the triplication arrivals in the inversion, a first for a deep mantle tomographic model, is possible because of the widespread presence of a $D^{\prime\prime}$ velocity discontinuity in the region. The additional raypath sampling provided by the triplication arrivals yields improved vertical resolution of velocity heterogeneity within and above the $D^{\prime\prime}$ region. The reference velocity model, taken from a prior study of waveforms in the region, has a 2.9% shear velocity discontinuity 250 km above the CMB. Effects of aspherical structure in the mantle at shallower depths than the inversion volume are suppressed by applying corrections for several different long-wavelength shear velocity tomography models. Born-Fr\'{e}chet kernels are used to characterize how the finite-frequency data sample the structure for all of the differential arrival time combinations; inversions are performed with and without the kernels. The use of 3-D kernels stabilizes the tomographic inversion relative to a ray theory parameterization, and a final model with 60 and 50 km correlation lengths in the the lateral and radial dimensions, respectively, is retrieved. The resolution of the model is higher than that of prior inversions, with 3 to 4% velocity fluctuations being resolved within what is commonly described as a circum-Pacific ring of high velocities. A broad zone of relatively high shear velocity material extends throughout the lower mantle volume beneath the Gulf of Mexico, with several percent lower shear velocities being found beneath northern South America. Concentrated low velocity regions extend through the $D^{\prime\prime}$ layer under the Caribbean, Colombia, and Ecuador, suggestive of small-scale plumes in the boundary layer. One scenario consistent with the imaged features involves subducted Farallon plate ponding at the base of the mantle and laterally displacing hot boundary layer material that piles up and destabilizes on its margins.
DE: 8130 Heat generation and transport
DE: 7207 Core and mantle
DE: 3919 Equations of state
DE: 1212 Earth's interior--composition and state (8105)
DE: 1507 Core processes (8115)
SC: Union [U]
MN: 2004 AGU Fall Meeting