Unclassified

crustal and site effects and instrument nonlinearity can be ruled out as factors significantly affecting the t * estimates obtained.,-The results indicate low attenuation under shields and old oceans and htgh/kttenuation under tectonic areas and new oceans. While t * in the long-period band is approximately 1.0 sect most of the short-period t * values are considerably less than 1.0 sec, even for paths involving a low Q mantle, such as the mantle under the western United States. The high frequency fall-off rates of P and S wave spectra, the shapes of spectral ratios as functions of frequency, and the sizes of the regional body wave amplitude anomalies impose tight limits on the possible values of short-period t*, in spite of uncertainties in the source properties. The presently available long-period and short-period Q studies cannot be reconciled by any reasonable value of constant Q, thus requiring a Q that is frequency dependent