منابع مشابه
Mantle discontinuities beneath Southern Africa
[1] Seismic velocity discontinuities within the top 1000 km of the Earth beneath southern Africa are imaged by stacking about 1300 source-normalized broadband seismograms recorded by the Southern African Seismic Experiment. The Moho, 410, and 660 kilometer discontinuities are clearly detected. The mean mantle transition zone thickness is 245 km, essentially the same as the global average, sugge...
متن کاملTectospheric structure beneath southern Africa
P-wave and S-wave delay times from the broadband data of the southern Africa seismic experiment have been inverted to obtain three-dimensional images of velocity perturbations in the mantle beneath southern Africa. High velocity mantle roots appear to extend to depths of at least 250 km, and locally to depths of 300 km beneath the Kaapvaal and Zimbabwe cratons. Thick roots are confined to the A...
متن کاملUpper mantle SH- and P-velocity structures and compositional models beneath southern Africa
We constrain SH and P wave velocity structures in the upper mantle beneath southern Africa, using triplicated phases recorded in the epicentral distance range of 11°–28° for one shallow event. We then explore thermal and compositional models appropriate for explaining the inferred seismic structures in the region. Both SH and P wave data suggest presence of a low velocity zone with velocity red...
متن کاملThermal, hydrous, and mechanical states of the mantle transition zone beneath southern Africa
Observations of P-to-S conversions from the seismic discontinuities near 410 and 660 km depth reveal the shoaling of the 410-km discontinuity and the deepening of the 660-km discontinuity beneath the Archaean cratons in southern Africa; consequently, the mantle transition zone is 20 km thicker than beneath post-Archaean regions and the global average. The discontinuity structure, combined with ...
متن کاملSeismic evidence for accumulated oceanic crust above the 660-km discontinuity beneath southern Africa
[1] High-pressure assemblages of subducted oceanic crust are denser than the normal upper mantle but less dense than the uppermost lower mantle. Thus subducted oceanic crust may accumulate at the base of the upper mantle. Direct observational evidence for this hypothesis, however, remains elusive. We present an analysis of a negativepolarity shear wave converted from compressional wave at a sei...
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ژورنال
عنوان ژورنال: Nature
سال: 2001
ISSN: 0028-0836,1476-4687
DOI: 10.1038/35090672