INTENSIFICATION OF A LOW-FREQUENCY COMPONENT OF THE CHILEAN TSUNAMI (MAY 1960) IN THE NORTHWEST PACIFIC

T. N. Ivelskaya and G. V. Shevchenko

Using numerical methods, I. V. Fain [6] studied frequency-selective properties of the shelf and the continental slope off the Pacific coast of the Kurils Island arc. The calculations showed that in the vicinity of the Southern and Northern Kurils, where the shelf is relatively vast and shallow, the largest intensification (by about five or six times) of tsunami waves coming from the open ocean occurs at periods of about 1.5 h. Based on spectral analysis of the Chilean (May 1960) tsunami records and similar numerical calculations [6], it is shown that the strengthening effect of the low-frequency component may also play an important role in the formation of the wave field on the coast of Japan, where it can be traced in more detail with a large number of tide stations. It is found that the periods of the main low-frequency maximum in the oscillation spectrum may vary widely depending on the bottom relief even at a relatively small distance between the stations. At the points with prevailing waves of 80-min periods, wave heights and material damage were higher than in the regions with weaker frequency-selective properties. An important condition of this intensification is the low-frequency component during wave formation at the seaquake focus, which was found in the records of stations in Peru, Ecuador, the southern United States, and some of the Pacific islands. In the vicinity of the focus, on the Chilean coast, the prevailing waves have considerably lower periods (~40—45 min).