Absence of short-period ULVZ precursors to PcP and ScP from two regions of the CMB

Details Absence of short-period ULVZ precursors to PcP and ScP from two regions of the CMB Absence of short-period ULVZ precursors to PcP and ScP from two regions of the CMB

Jan 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001georl..28..387p&link_type=abstract

Geophysical Research Letters, Volume 28, Issue 2, p. 387-390

Physics

18

Seismology: Body Wave Propagation, Seismology: Core And Mantle, Tectonophysics: Dynamics Of Lithosphere And Mantle-General, Tectonophysics: Earth'S Interior-Composition And State

Scientific paper

We present results from a study of the coremangle boundary (CMB) underneath Mexico, Central America, and the northeast Pacific using core-reflected phases PcP and ScP, which provide a direct means of sampling the deep mantle. Precursor arrivals to these phases produced by reflection from the top of an ultra-low velocity layer (ULVZ) at the base of the mantle would contain information about the thickness of such a layer and the velocity reductions within it. Stacks of these phases from 17 earth-quakes recorded by the Northern and Southern California Seismographic Networks do not exhibit coherent or incoherent precursor arrivals from a ULVZ. In precursor time windows, ratios of stack amplitudes to those of the CMB-reflected phases fall below predicted values from published ULVZ models. We conclude that ULVZs, if present in these regions, have VP and VS reductions less than 10%, are less than five km thick, or have transitions greater than five km wide at their upper boundaries.

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