1. SPECTRAL ANALYSIS OF THE 1960 CHILE TSUNAMI RECORDS FOR NEARFIELD AND FARFIELD MEASUREMENTS T.N. Ivelskaya 1, G.V. Shevchenko 2 1 - Sakhalin Tsunami Warning Center, Yuzhno-Sakhalinsk, Russia 2 - Laboratory of Biological Oceanography,SakhNIRO, Yuzhno-Sakhalinsk, Russia

2. Pacific Ocean epicenter of quakes tide-gauge stations 2001 1960

3. Arika Antofagasta Coquimbo Valparaiso The nearfield records along the coast of Chile 1960 Chile tsunami

4. Antofagasta Arika Coquimbo Valparaiso The most common peak with period of about 45 min is probably related to the cross-section size of the source. Other peaks are apparently related to the local topographical effects (shelf resonance and natural bay oscillations). Frequency (cpm) Nearfield tsunami records Tsunami spectra

5. Pacific Ocean Sea of Okhotsk Sea of Japan Location of tide-gauge stations with digitized records used in the present study

6. Yuzhno-Kurilsk Hanasaki Hachinohe Miyako Kamaishi Nakaminato Choshi The farfield 1960 tsunami records (on the northwestern coast of the Pacific Ocean )

7. Tsunami spectra Farfield tsunami records The typical feature of the “farfield spectra” is relative amplification of the lowfrequency component and significant decay of the highfrequency oscillations. Frequency (cpm) Yuzhno-Kurilsk Hanasaki Hachinohe Miayko Kamaisi Choshi Nakaminato

8. Malokurilsk Hanasaki Kushiro Malokurilsk Hanasaki Kushiro Farfield tsunami records 2001 Peru tsunami Tsunami spectra The 2001 Peru tsunami was weaker, however, the main effects were the same: relative amplification of lowfrequency component and significant decay of highfrequency oscillations.

9. Conclusions: 1.Based on analysis of the 1960 Chile tsunami, significant difference is found to exist between nearfield and farfield tsunami records and corresponding tsunami spectra: the source parameters determine the nearfield spectra, while topographic effects determine the character of the farfield spectra. 2. The major period of the observed nearfield spectra, 45 min, is apparently related to the cross-shore dimension of the source, while 80-min period that prevailed in the spectra of the Kuril and Japanese stations is associated with the major resonant period of the continental shelf in this region.

10. 3. In general, the farfield spectra are characterized by relative amplification of the lowfrequency component and clear decay of the highfrequency component. 4. The analysis of the Peru tsunami of June 23, 2001, gave very similar results and support these conclusions. 5. The physical difference between the character of far- field (distant) and nearfield (local) tsunamis should be taken into account by Tsunami Warning Services.

11. Thank you!