SPECTRAL ANALYSIS OF THE 1960 CHILE SPECTRAL ANALYSIS OF THE 1960 CHILE TSUNAMI RECORDS FOR NEARTSUNAMI RECORDS FOR NEARFIELDFIELD AND AND

FARFIELD MEASUREMENTSFARFIELD MEASUREMENTS

T.N. IvelskayaT.N. Ivelskaya11, G.V. Shevchenko, G.V. Shevchenko22

1 - Sakhalin Tsunami Warning Center, Yuzhno-Sakhalinsk, Russia1 - Sakhalin Tsunami Warning Center, Yuzhno-Sakhalinsk, Russia

2 - Laboratory of Biological Oceanography,SakhNIRO, Yuzhno-Sakhalinsk, Russia2 - Laboratory of Biological Oceanography,SakhNIRO, Yuzhno-Sakhalinsk, Russia

Pacific Ocean

epicenter of quakes

tide-gauge stations

2001

1960

-150

-100

-50

0

50

100

150

23.0

5

24.0

5

25.0

5

26.0

5

Арика

-150

-100

-50

0

50

100

150

23.0

5

24.0

5

25.0

5

26.0

5

Кокимбо

-150

-100

-50

0

50

100

150

23.0

5

24.0

5

25.0

5

26.0

5

Вальпараисо

-150

-100

-50

0

50

100

150

23.0

5

24.0

5

25.0

5

26.0

5

Антофагаста

Arika

Antofagasta

Coquimbo

Valparaiso

The nearfield records along the coast of Chile

1960 Chile tsunami

0

500

1000

1500

2000

2500

0.001 0.01 0.1 1

Антофагаста

Арика

0

500

1000

1500

2000

2500

0.001 0.01 0.1 1Частота, цикл/мин

Кокимбо

Вальпараисо

`

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

Pacific Ocean

Sea of

Okhotsk

Seaof

Japan

Location of tide-gauge stations with digitized records used in the present study

-200

-150

-100

-50

0

50

100

150

200

0 6 12 18 0 6

Ханасаки

-100

-50

0

50

100

150

200

0 6 12 18 0 6

Южно-Курильск

-300

-200

-100

0

100

200

300

400

0 6 12 18 0 6

Хачинохе

-100

-50

0

50

100

150

0 6 12 18 0 6

время, ч

Мияко

24.05.1960 25.05.1960

Yuzhno-Kurilsk

Hanasaki

Hachinohe

Miyako

-100

-50

0

50

100

150

200

0 6 12 18 0 6

Накаминато

-150

-100

-50

0

50

100

150

200

0 6 12 18 0 6

Камаиси

-150

-100

-50

0

50

100

150

200

250

0 6 12 18 0 6

время, ч

Чоши

24.05.1960 25.05.1960

Kamaishi

Nakaminato

Choshi

The farfield 1960 tsunami records (on the northwestern coast of the Pacific Ocean )

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.

10

100

1000

10000

100000

1000000

0.0001 0.001 0.01 0.1 1частота, цикл/мин

Южно-Курильск

Ханасаки

Хачинохе

10

100

1000

10000

100000

0.0001 0.001 0.01 0.1 1частота, цикл/мин

Мияко

Камаиси

10

100

1000

10000

100000

1000000

0.0001 0.001 0.01 0.1 1частота, цикл/мин

Чоши

Накаминато

Frequency (cpm)

Frequency (cpm)

Frequency (cpm)

Yuzhno-Kurilsk Hanasaki Hachinohe

Miayko Kamaisi

Choshi Nakaminato

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

1

36

1

72

1

10

81

14

41

18

01

21

61

25

21

28

81

Малокурильское

-30

-20

-10

0

10

20

30

40

1

36

1

72

1

10

81

14

41

18

01

21

61

25

21

28

81

Ханасаки

-25

-20

-15

-10

-5

0

5

10

15

20

1

36

1

72

1

10

81

14

41

18

01

21

61

25

21

28

81

Кусиро

0

1000

2000

0,001 0,01 0,1 1

Малокурильское

0

1000

2000

3000

4000

0,001 0,01 0,1 1

ХанасакиКусиро

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.

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.

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.

Thank you!