We study the lateral variations in shear wave attenuation in the upper
mantle by analyzing the spectra from S and SS arrivals from selected
long-period seismograms between 1976 and 1999. We use seismograms from
shallow earthquakes ( 50~km depth) at epicentral distances of
40°-80° for S waves and 80°-160° for SS waves. Each
spectrum is the product of source, receiver, and propagation response
functions as well as local source- and receiver-side effects. We correct
each spectrum for the known instrument response, a source model with an
 -2
falloff at high frequencies, and a one-dimensional
Q model. Since there are multiple receivers for each source
and multiple sources for each receiver, we can approximate the source-
and receiver-side terms by stacking the appropriate S log spectra. The
resulting source-specific response functions include any remaining source
spectrum and the effect of near-source attenuation in the upper mantle;
the receiver stacks include the site response and near-receiver Q
structure. We correct the SS log spectra for the appropriate source-
and receiver-side stacks found from the S waves. Since attenuation in
the lower mantle is small, the residual SS log spectrum approximates
attenuation in the upper mantle near the SS bounce point, and can be
used to estimate  at frequencies between 0.023~and 0.086~Hz.
The resulting bounce point measurements, which we smooth
into caps of 5° radius, show spatially coherent patterns of more and
less attenuating regions.
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