Frequency Dependence of Q in the Mantle Underlying the Shield Areas of Eurasia

Abstract : In Part I; the results of short and intermediate period data analyses for the determination of a frequency dependent Q model of the mantle under the shield areas of Eurasia are presented. The spectra of short period P waves from nuclear explosions in the 1-8 Hz frequency range give t* sub p = approx. 0.15-0. 2 seconds. Part II presents analyses of long period data. Long period multiple S and ScS phases observed in northern Europe were analyzed to determine mantle attenuation in the 0.02 to 0.2 Hz range under the Eurasian shield. Two groups of events are used: deep Far-Eastern earthquakes and large earthquakes near the edges of the shield areas of Eurasia. Part III provides the Q model. A large set of broad band data was analyzed to determine the frequency and depth dependence of Q for P and S waves under the northern shield areas of Eurasia. A wide range of techniques utilizing spectra, amplitude ratios and waveform modeling were used to derive apparent and absolute t* estimated for P and S waves covering the seismic band between 0.01 to 10 Hz. A supplement discusses methodologies for estimating t*(f) from Short Period Body Waves and Regional Variations of t*(f) in the United States. Keywords include: Attenuation.