Geoscience Reference
In-Depth Information
Fig. 6.7
Tide records or
marigrams of the May 22, 1960
Chilean Tsunami around the
Pacific Ocean. Records have had
their daily tides removed. Based
upon Wilson et al. (
1962
), Tsuji
(1991)
, and Heinrich et al. (
1996
)
Valparaiso, Chile
Santa
Monica
1.0
0.5
0.0
0.0
-0.5
-1.0
0
4
Hours after earthquake
2
6
14
16
18
20
22
24
26
Hours after earthquake
10
Nuku-Hiva
Tahiti
1.0
5
0
0.0
-5
-1.0
-10
10
11
Hours after earthquake
12
13
14
10
11
12
13
14
Hours after earthquake
Hilo
Hanasaki
Japan
1.0
1.0
0.0
0.0
-1.0
-1.0
14
16
18
20
22
24
26
28
21
22
23
24
25
26
27
28
29
Hours after earthquake
Hours after earthquake
slopes existed and bays were present, wave heights were
amplified by a factor of five and run-ups averaged 4.3 m.
Hence, outside the source region, the Pacific Islands were
affected the most by the tsunami. For example, on the
Marquesas Islands, the wave height of the second wave
exceeded 10 m at Nuku-Hiva and Hiva-Oa (Fig.
6.7
). Here,
the wave ran up valleys 500 m inland. The largest run-up on
any Pacific island, 12.2 m, occurred on Pitcairn Island.
Hawaii was particularly affected by the tsunami that
refracted around to the north side of islands (Lander and
Lockridge
1989
; Pararas-Carayannis
1998a
). The greatest
impact occurred at Hilo. Here, after traveling 10,000 km
over a period of 14.8 h, the tsunami's arrival time at 9:58
AM was predicted to within a minute. In spite of more than
5 h warning, only 33 % of residents in the area affected in
Hilo evacuated. Over 50 % only evacuated after the first
wave arrived, and 15 % stayed behind even after the largest
waves had beached. The first two waves did not do much
damage, but the third wave was deadly. It swept inland 6 m
above sea level, reaching a maximum run-up of 10.7 m.
Sixty-one people were killed as the wave swept ashore.
Many of those killed were spectators who went back to see
the action of a tsunami hitting the coast. The waterfront at
Hilo was devastated as the waves swept inland over five city
blocks (Fig.
6.8
). 10 tonne vehicles were swept away and
20 tonne rocks were lifted off the harbor's breakwall and
carried inland 180 m. In the area of maximum destruction,
only buildings of reinforced concrete or structural steel
remained standing. Wooden buildings were either destroyed
or floated inland, and piled up at the limit of run-up. About
540
damaged. Damage in Hawaii was estimated at $24 million.
Subsequently the flooded area was turned into parkland to
prevent a recurrence of the disaster.
Although warnings were issued for Japan, the waves
struck this country very unexpectedly 22 h after being
generated (Committee of the Field Investigation of the 1960
Chilean Tsunami
1961
). The tsunami rose from 40 to 70 cm
height in 200 m depth of water despite losing 40 % of its
energy traveling across the Pacific. Dispersion dramatically
reduced the height of the initial waves in the tsunami wave
train. This effect is shown by the marigram for Hanasaki,
Japan, in Fig.
6.7
. In addition, resonance effects tended to
enhance isolated waves in the wave train such that the
maximum run-up occurred hours after the arrival of the first
waves. Run-up heights averaged 2.7 m along the east coast,
with a maximum value of 6.4 m recorded at Rikuzen. At
Shiogama and Ofunato on the Sanriku coast of northern
Honshu—where local earthquakes, but not distant Pacific
ones, had produced such devastating tsunami over the past
century—fishing boats were picked up and flung into
business districts. Seiching at wave periods much lower
than that of the main tsunami occurred in many harbors.
Along the shoreline of Hokkaido and Honshu, 5,000 homes
were washed away, hundreds of ships were sunk, 251
bridges were destroyed, 190 people lost their lives, and 854
were injured. Over 50,000 people were left homeless, with
property damage estimated at over $350 million (Myles
1985
).
At the beginning of this section, a 30-50 year interval
was mentioned for the occurrence of significant tsunami-
genic earthquakes along the Chilean coast. The 1960 event
homes
and
businesses
were
destroyed
or
severely
