Rayleigh Wave Spectra and Group Velocity Minima, and the resonance of P waves in layered structures |
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Authors: | J A Hudson A Douglas |
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Institution: | J. A. Hudson: Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge CB3 9EW.;A. Douglas: MOD(PE), Blacknest, Brimpton, Reading RG7 4RS, Berkshire. |
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Abstract: | Summary. A connection is established between the group velocity of Rayleigh waves, the spectral amplitudes of surface waves generated by a source, and the resonance of vertically travelling P waves. It implies that a minimum in a group velocity curve is reflected in the spectral amplitudes as a maximum. That this is so, appears to have been first noticed by Longuet-Higgins in a study of microseisms. Also when a sharp impedance contrast occurs in a plane-layered model of the crust, the group velocity minimum in the fundamental mode occurs close to a period equal to four times the travel time of P -waves from the surface to the interface. More than one such contrast gives rise in general to more than one minimum. Similar relations hold for the higher modes. |
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