Love-wave excitation due to the interaction between a propagating ocean wave and the sea-bottom topography

This study formulates Love-wave excitation in terms of the interaction between a propagating ocean wave and the sea-bottom topography. By assuming a Fraunhofer diffraction range, or far-field approximation, I theoretically derive an equivalent point force for the Love-wave excitation. The equivalent point force acts in the same direction as the propagation direction of the ocean wave. The excited Love wave has a radiation pattern characterized by sin θ, where θ is the angle between the propagation directions of the Love and ocean waves. The efficiency of the excitation is then investigated by employing both deterministic and stochastic models for sea-bottom topography. When a seamount given by a Gaussian function is used as a deterministic model, the equivalent point force has a narrow peak against the wavenumber of the ocean wave; a strong interaction occurs at λ= 2.2d, where λ is the ocean-wave wavelength and d is the characteristic scale of the seamount. On the other hand, when randomly fluctuating sea-bottom topography characterized by a power-law spectrum is used, the interaction can occur over a wide range of the ocean wave wavelength.