Geoscience Reference
In-Depth Information
Fig. 6.6
Aerial view of Isla
Chiloe, Chile, showing damage
produced by the May 22, 1960
Tsunami. Two hundred deaths
occurred here. Source National
Geophysical Data Center,
http://
establishment of the modern Pacific Tsunami Warning
System. The tsunami reached landfall first along the Mex-
ican, New Zealand, and Australian coasts (Fig.
6.5
). It
travelled quickest northwards along the coast of the
Americas across the North Pacific Ocean to Japan. The
wave crest underwent refraction around islands in the west
Pacific, particularly those in the Izu-Bonin and Marianas
Island arcs. Detailed wave refraction analysis indicates that
energy was focused towards Japan in the northwest Pacific,
but dispersed elsewhere.
These effects are reflected in marigrams derived from
tidal gauge records around the Pacific Ocean (Fig.
6.7
). The
marigrams show multiple peaks, the highest of which
occurred sometime after the arrival of the first wave at some
locations (Wilson et al.
1962
Tsuji
1991
; and Heinrich et al.
1996
. Run-ups for the event are summarized by region in
Table
6.1
. In the Southwest Pacific, the tsunami entered the
Tasman Sea from the south about 12 h after the earthquake
and caused rapid fluctuations in water levels in many har-
bors. Run-ups averaged 0.5-0.6 m respectively along the
east coasts of New Zealand and Australia, reaching maxi-
mum values of 1.8 m. Boats were torn from their moorings
or beached by currents generated by tsunami-induced sei-
ching. Along the coastline of the Americas, where the coast
bends eastwards, the tsunami had minimal effect with run-
ups averaging only 40 cm. On the exposed sections of the
west coast of the United States, wave run-up averaged
1.2 m, with values ranging between 0.2 and 3.7 m. The
tsunami also had a variable impact on Pacific Ocean islands
(Heinrich et al.
1996
). On smaller islands fronted by steep
offshore slopes and protecting fringing reefs, waves were
only 1-2 m in height. However, where gradual bottom
Table 6.1
Statistics on the run-up heights of the May 22, 1960
Chilean Tsunami around the Pacific Ocean
Region
Average
height (m)
Maximum
height (m)
Range (m)
Source area
12.2
25.0
8.5-25.0
Chile
2.7
5.0
0.4-5.0
Peru
2.0
3.9
1.0-3.9
Central America
0.5
1.4
0.2-1.4
US West Coast
1.2
3.7
0.2-3.7
Canada
0.4
0.4
0.1-0.4
Alaska
1.3
3.3
0.4-3.3
Hawaii
3.1
10.5
1.5-10.5
Pacific Islands
4.3
12.2
0.5-12.2
Japan
2.7
6.4
0.2-6.4
New Zealand
0.6
0.9
0.4-0.9
Australia
0.5
1.8
0.2-1.8
Over the next 24 h, a series of tsunami wave crests
spread across the Pacific, taking 2,231 lives and destroying
property in such diverse places as Hawaii, Pitcairn Island,
New Guinea, New Zealand, Japan, Okinawa, and the Phil-
ippines. Figure
6.5
shows the arrival time of the tsunami
across the Pacific (Wiegel
1964
; Pickering et al.
1991
). The
initial wave travelled at a speed of 670-740 km hr
-1
,
depending upon the depth of the ocean. Individual waves in
the tsunami wave train had wavelengths of 500-800 km and
periods of 40-80 min. In the open ocean, the wave height
was only 40 cm high. The tsunami was measured at 630
sites around the Pacific Ocean. It is the most widespread
tsunami to affect this basin. It was also responsible for the
