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PACIFIC SCIENCE, Vol. XXI, July 1967 
limit to extend to the west side of Shelikof 
Strait and Cook Inlet. 
In estimating the travel time of the tsunami, 
corrections were made for the delay at the is- 
land of Kodiak in the arrival of the ground 
shocks from Prince William Sound. These cor- 
rections ranged from 1 minute to 6 minutes and 
were based on the fact that the Navy Weather 
Central on the island of Kodiak listed the time 
of the principal shock in Prince William Sound 
as 6 minutes later than the time listed by the 
U. S. Coast and Geodetic Survey. This would 
imply that the wave front generated on the 
northeast side of the disturbance area had a 6- 
minute head start on the wave front generated 
southeast of Kodiak. 
The tsunami-generating area covers an area 
700 km long by 150 km wide, a total of about 
105,000 km 2 . The volume of the uplifted crust 
along the continental shelf is about 96 km 3 . The 
energy associated with the tsunami has been 
estimated by Van Dorn (1964) to be of the 
order of 2.3 X 10 21 ergs. This estimate is based 
on the source dimensions of an area 240 nau- 
tical miles by 100 nautical miles and an uplift 
of 1.8 m (6 ft) at the northeastern end of this 
area and zero at the southwestern end. This 
estimate, however, is considered low because the 
generating area had dimensions that were larger 
than those estimated by Van Dorn. 
Using our source dimensions, and assuming 
that the total energy was equal to the potential 
energy of the uplifted volume of water, the 
total energy for the tsunami in the Gulf of 
Alaska was calculated as follows: 
E t = \gh 2 A 
6 
1 
= — (1-03) (.980) (10 3 ) (10 4 ) (1.83 2 ) (1.5 
6 
X 10 7 ) (7 X 10 7 ) = 5.88 X 10 21 ergs 
where 
E t = E p = total energy 
p — 1.03 g/cm 3 = density 
g = 980 cm/sec 2 
h = height of displacement =1.83 m 
A = area 
1 erg = g cm 2 sec -2 
The waves generated in the Gulf of Alaska 
were of an unusually long period, on the order 
of an hour or more. Their energy radiation was 
preferentially directed toward the southeast and 
this is why more damage was done to the North 
American coast than anywhere else east or south 
of the generating area. This preferential direc- 
tivity of energy radiation can be attributed to 
the orientation of the tectonic displacements 
along the continental shelf of the Gulf of 
Alaska, and the long period of the waves can 
be related to the long seiche period of the 
shallow shelf. 
According to Japanese seismologists (Iida, 
1958), the generating area of a tsunami roughly 
corresponds to the distribution of the major 
aftershocks. This appears to be indeed the case 
in the Gulf of Alaska. 
There were 52 aftershocks of the Alaska 
earthquake. The largest had a magnitude of 6.7. 
The aftershocks occurred in an area from about 
15 km north of Valdez to about 55 km south of 
Trinity Islands, and were heavily concentrated 
on the northeast and the southwest of the up- 
lifted region (USCGS, 1964), which also was 
the main tsunami-generating area. 
The vast area of tectonic movements indicates 
that wave crests were generated along one or 
more line sources from the region of maximum 
uplift. Thus, the shores of the Kenai Peninsula 
were struck within 20 minutes after the start of 
the earthquake, and those of Kodiak Island, 
within 34 minutes. 
Unfortunately, the violence of the earthquake j 
left south-central Alaska without a tide gauge | 
in operation. The only reliable record from the | 
generating area is the one that was obtained by 
personnel of the U. S. Navy Fleet Weather 
Station at Kodiak; it is shown in Figure 2. This | 
record has been corrected for the 1.7-m (5.6-ft) 
submergence of the area. 
Outside the immediate generating area, the 
record of Cape Yakataga, as constructed from 
the personal account of C. R. Bilderback, a resi- 
dent of the area, is the next most reliable record, j 
This record is the only one obtained outside 
the generating area that shows an initial drop 
in the water level (Berg et al., in preparation). 
Withdrawal of the water immediately following 
the earthquake has been reported from Kayak, 
Middleton, and Hinchinbrook islands, as well 
as from Rocky Bay and Nuka Bay, at the end 
