A Model Experiment of the Tunami in the Osaka Bay caused by the Earthquake

[摘要] Earthquakes which occurred in the Pacific Ocean near Japan were so often accompained with tunamis that among 50 great earthquakes almost half were followed by them.The Osaka bay is communicated with the Pacific Ocean through the Yura straits. Though the Yura straits is narrow, it is so deep that the Osaka bay was often attacked by tunami. Present authors made an experiment on the tunami of the Osaka bay by a model, the horizontal and vertical ratios to the Osaka bay being 1:135000 and 1:1000 respectively. The model was put in the water tank, its length, breadth and height being 1.85cm, 75cm, 50cm; and the tunami wave was generated by a brass plate by pulling or pushing it longitudinally in the tank (Fig. 1. in the text). On 13 points in the bay the tunami was recorded on the rotating film by using small tide-gauges (Fig. 3) specially deviced for this experiment.Results of experiment show that in the middle of the Osaka bay the oscillation is much different from that which occurs at each end of the longer axis of the bay.In the middle of the bay, -(1) the amplitude is small, (2) the fourth wave has the largest amplitude, (3) oscillations are irregular, (4) the first wave is comparatively large.On the contrary at both ends, -(1) the amplitude is large, (2) the second wave has the largest amplitude, (3) oscillations are regular, (4) the first wave is comparatively small.The height of tunami is largest near the coast of Sakai which is about 2.5 times large as that experienced in Yura straits. On the coasts of Osaka and Nisinomiya it is 2.2, 1.7 times large respectively, and at other places it is nearly equal to that experienced in the Yura str its.

[学科分类] 大气科学