Me. Wysession et al., Using MOMA broadband array ScS-S data to image smaller-scale structures atthe base of the mantle, GEOPHYS R L, 28(5), 2001, pp. 867-870
ScS-S residuals obtained at stations of the Missouri-to-Massachusetts (MOMA
) temporary broadband seismic array are used to delineate variations in sei
smic velocity structure above the core-mantle boundary (CMB) at scales smal
ler than observable with tomographic models. South American earthquakes rec
orded at MOMA reveal a slow-velocity anomaly that is at least as small as t
he limit of the resolution of ScS waves, about 300 km across. This is model
ed as being within a region of fast velocities in whole-mantle models. The
slow ScS-S residuals correlate well with a peak in ScS/S relative amplitude
s. The small region of slow shear velocity at the CMB could be a pocket of
lower mantle rock trapped beneath the descending Farallon slab, or evidence
of chemical boundary layer variations.