abstract

By means of a recently developed finite element technique, the propagation of Love and Rayleigh waves along an approximately north-south section of the San Fernando Valley is studied. At periods of 1 sec or less, the surface amplitudes of both Love and Rayleigh waves increase considerably with distance south into the valley as the alluvium thickens. Dipping structures give rise to higher Love and Rayleigh modes which modulate the surface displacement caused by the fundamental Love and Rayleigh modes. At periods of 1 sec or less, the fundamental Love and Rayleigh modes travel almost entirely in the uppermost 9000 ft (2743 m) of the Earth's crust. Conversion of the first higher Love mode to the fundamental mode can contribute significantly to the Love wave surface displacement. Finally, at periods of 1 sec or less, the phase velocities of the fundamental Love and Rayleigh modes depend on the displacements of these modes near the surface of the Earth. These velocities may be considerably different from the arithmetic mean of the phase velocities of the Love and Rayleigh modes at the ends of the model.

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