1936 Volume 14 Issue 7 Pages 348-370
On Oct. 1st, 1918 a severe typhoon passed through the western side of the Tôkyô city. On this account some parts of the coast of the Bay were attacked twice by high waters of Tunami(1) and the time interval between the first and second attack was observed as 90 minutes.
These Tunami waves were already considered by some authors as the proper oscillation of this bay, for instances Prof. S. Nakamura as the secondary undulation of the 3rd order and Prof. F. Omori, a sort of a secondary undulation of the Sinagawa Bay, which is one of the inlet of the Tôkyô Bay. But the author's opinion is somewhat different from the above two, for he considers it as a lateral oscillation of the Tôkyô Bay. This consideration is made by following facts that The tunami waves attacked Yokohama and the mouth of the Yedogawa River at the same time where both situate at the western coast of the Tôkyô Bay, and moreover the author has obtained theoretically the period of the lateral oscillation to be about 90 minutes, assuming the bay to be a rectanglar lake with length of 53'8km. breath of 22km and depth distribution to be h=h0(1+x/a) where h0=26m, a one half of length. The period thus obtained just coincides with the observed one. Besides the lateral oscillation, it seems to exist then a longitudinal one, which came as a solitary wave at the northern coast of the bay.
Next, the author has tried to obtain theoretically the hight and the time of occurrence of Tunami at some places of western coast, assuming that these oscillations be cansed by daynamical effect of suction due to travelling atmospheric depression. The results thus obtained show that 1) when the typhoon passes the western side of the rectangular bay parallel to its length, the arrival of the longitudinal wave at the northern coast is delayed by 1/2(Ta+a/c) compared with the time of the entrance of the center of a typhoon in or beside the bay, where Ta is the period of the longitudinal oscillation of the bay. 2) and the arrival of the first lateral wave to the western coast is delayed by 1/4T_??_ compared with the time of entrance of the typhoon center in or beside the bay, where T_??_ is the period of the lateral oscillation. These results also agree considerably well with observed fac's.