Research in Seismology
Semi-annual technical rept. no. 2, 1 Apr-30 Sep 1979
SAINT LOUIS UNIV MO DEPT OF EARTH AND ATMOSPHERIC SCIENCES
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Research was concerned with observational and theoretical aspects of the attenuation of short-period seismic phases in the eastern United States and southern Asia, and of the corresponding Q structure of the earths crust. The attenuation of the short-period fundamental-mode Rayleigh waves in the eastern United States can be explained either by a frequency-independent or frequency- dependent model of shear wave internal friction. However, in order to fit the observed value of 1 to 10-sec period, first higher-mode Rayleigh waves, a frequency-dependent model is required. Additional higher-mode observational data at periods between 1 and 4 sec are required to determine the exact form of the frequency dependence. Stochastic inversion techniques were applied to Rayleigh wave data to determine Q beta models for three regions of the United States. The results of this study indicate that upper crustal Q beta values in the western United States are significantly lower than in the eastern United States. Colorado Plateau values are intermediate between those of the Basin and Range and the eastern United States.