Secondary undulations locally called "Abiki" are frequently observed in Urauch Bay in Koshiki Islands. A meteorological disturbance over the East China Sea has been pointed out as the cause of the secondary undulations. In this study, response characteristics of the East China Sea to propagating pressure waves and the oscillation property of Urauch Bay were evaluated by numerical analyses. As the result, it is clarified that pressure waves with phase velocity of 80-140 km/h and spatial scales of 10-40km lead to large fluctuations of water level which have the periods close to the natural period of Urauch Bay. The waves close to the natural period not only set up resonance in the bay but also produce oscillations with a half period of incident waves in Urauch Bay.
