Shear Velocity Structure in the Eastern United States from the Inversion of Surface Wave Group and Phase Velocities
SAINT LOUIS UNIV MO DEPT OF EARTH AND ATMOSPHERIC SCIENCES
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Single-station group velocities at periods between 4 and 70 seconds and single-station phase velocities at periods between 10 and 50 seconds are obtained for a broad region of the eastern United States for both Rayleigh and Love waves. These data were obtained by the single-station method using earthquakes with known fault-plane solutions in the central United States. The group velocity data are combined with earlier acquired attenuation data to yield Q values for Rayleigh and Love waves in the eastern United States. Inversions of the dispersion curves for shear-velocity models of the crust and upper mantle indicate that all of the data can be explained satisfactorily by a single model which is isotropic in its elastic properties. This model includes a surface layer of low-velocity sediments, and is characterized by upper crustal shear- wave velocities which increase from 3.4 to 3.7 kmsec with increasing depth, by lower crustal shear-wave velocities between 4.0 and 3.8 kmsec, and by an upper- most mantle shear-wave velocity of about 4.8 kmsec. The fundamental-mode data of this study do not require a low-velocity zone in either the crust or upper mantle. Higher-mode velocities and wave forms, although having potentially greater resolving power than the fundamental-mode data, were too inconsistent to contribute to the elucidation of detailed features of the crust-upper mantle model.