HR: 0800h
AN: S31B-01    [Abstracts]
TI: Localized seismic scatterers near the core-mantle boundary beneath the Caribbean Sea: evidence from PKP precursors
AU: * Miller, M S
EM: meghan.s.miller@rice.edu
AF: Rice University, Department of Earth Science 6100 Main St, Houston, TX 77005, United States
AU: Niu, F
EM: niu@rice.edu
AF: Rice University, Department of Earth Science 6100 Main St, Houston, TX 77005, United States
AB: The nature of the core-mantle boundary (CMB) region, the D", has been a focus of research for decades because it is a crucial part in understanding the evolution of geodynamics and whole earth structure. The D" region is very heterogeneous and has complicated seismic structures that require involvements of both chemical and thermal processes. One representative and well studied area is Central America and Caribbean, where the D" region is featured by a well defined seismic discontinuity underlain by anisotropic and higher velocity materials. Here we used seismic phase arrivals from earthquakes in the Western Pacific recorded by broadband seismic stations in northern South America and the Caribbean to investigate the core-mantle boundary and the D" region beneath the central Caribbean plate. We identified precursors to the PKP phases in 14 events, which can be explained by a region of heterogeneous scattering located above the CMB beneath the central Caribbean plate. The seismic scatterers are localized to the vicinity between approximately 5°N to 20°N and -80°W to - 65°W. Other similar distance events that display no precursors, interpreted to have traversed non- scattering regions on the core-mantle boundary, lie to the south and southwest of the identified cluster of seismic scatterers. We found that the small-scale seismic scatterers are not uniformly distributed, are concentrated, and are surrounded by relatively fast shear velocity perturbations in the lower mantle imaged with global seismic tomography. The fast velocity perturbations may be residual slab from the subducted Farallon plate and the scatterers to the east-northeast of the high velocity material could be remnants of heterogeneous material, perhaps former basaltic crust, that has been transported ahead or on top of the subducted slab material as it impacts and bends at the core-mantle boundary.
DE: 7207 Core (1212, 1213, 8124)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Seismology [S]
MN: 2007 Joint Assembly