Long-period Waves in the Vicinity of Onagawa Bay (I):Field Measurements in Onagawa and Okachi Bays

概要

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To investigate the response characteristics of a bay to tsunamis, field measurements of long-period waves have been carried out at Onagawa and Okachi Bays, both of which face the Pacific Ocean in northern Japan. In Onagawa Bay, the observed transfer function is in good agreement with the prediction based on the one-dimensional numerical model, in the period range larger than about 15 minutes. The response of shorter periods seems to be influenced by the two-dimensionality of the bay. The oscilla ions within Onagawa Harbor are also discussed with respect to the relative amplitude and phase at two stations inside the harbor and it is estimated that the reflection coefficient at the waterfront s about 0.7. In Okachi Bay, the oscillations in the period range larger than about 10 minutes could be explained by a Y-shaped model of the bay. The dominant oscillations offshore of these two-bays are found to be the mode with the motion predominantly in the direction normal to the shelf orientation, and the estimated power spectral density of incoming waves in deep water varies asf-2, fbeing the frequency. The waves of lateral modes, such as edge waves on the shelf, are small and of minor importance to generate bay oscillations of longer periods.
日本海洋学会の論文