Tunami Wave in Osaka Bay. (IV)

[摘要] In this paper we have calculated the time duration in which a tunami wave travels through the whole course of the Kii Channel. We assumed that the initial position of the wave front of tunami is on the straight line connccting Siomisaki and Murotomisaki, and that it advances northwards holding straightness of its frontal line with the velocity √gh as the wave length of tunami is very large, where g is the gravity acceleration and h the mean deapth of the vertical section of the channel containing a frontal line. Then dividing the total course into 20 wave fronts as is shown in Fig. 1, and summing up the time elements which is given by where dx is the distance betwecn two adjacent frontal lines and H the mean of their h, we get the travel time as is shown in Fig. 2.On the other hand, we calculated numerically the travel time by means of the equations where f is the wave amplitude, V the velocity, S and b the sectional area and breadth of the channel respectively (Cf. our previons papers). In our case the initial condition is V=√gh0 and the period is 20 or 40 miniutes. The results are shown also in Fig. 2.As we see from Fig. 2, the travel time passing through the Kii Channel is just 60 minutes and the same for our three cases. We have seen in the previous papers that tunami requires 60 minutes to travel through the whole course of the Osaka Bay so that it takes just two hours from the entrance of the Kii Channel to the City of Osaka. This fact gives time enough to make a watcher at, say, Siomisaki to warn the city against the tunami.

[学科分类] 大气科学