Alaska Earthquake and Tsunami, I — -Pararas-Carayannis 
303 
is greater than the 1906 San Francisco earth- 
quake (8.3), and equal to or greater than the 
I960 Chile earthquake (8.4). The epicenter 
of the earthquake was at 61.05° N, 147.7°W 
(USCGS, 1964), near the east shore of Una- 
kwik Inlet in northern Prince William Sound. 
Geological investigations have defined the 
land areas affected by the earthquake. To the 
east, the zone of deformation appears to die out 
between the Bering Glacier and Cape Yakataga. 
The northwestern limit of tectonic changes 
extends at least to the west side of Shelikof 
Strait and Cook Inlet (Plafker, 1965). The 
north inland limit is known only along the 
highway connecting Valdez and Fairbanks; it 
appears to extend in a northeasterly direction 
to the vicinity of the Wrangell Mountains, and 
quite possibly into the Alaska Range. 
The area of uplift covers about 105,000 km 2 
and extends from southern Kodiak Island north- 
east to Prince William Sound. It includes the 
southern and eastern parts of Prince William 
Sound, the coastal area as far east as the Bering 
Glacier, and the continental shelf and part of 
the slope to a depth contour of approximately 
200 m. The maximum uplift on land was 10 m 
at the southwest end of Montague Island, but 
is suspected to have been considerably more off- 
shore. Uplift also occurred along the extreme 
southeastern coasts of Kodiak Island and Sitka- 
lidak Island, and part or all of Sitkinak Island. 
The maximum measured uplift of Sitkalidak 
Island was 0.4 m. The estimated uplift of Sit- 
kinak Island was from 0.35 to 0.65 m and pos- 
sibly as much as 1.5 m (Plafker, 1965). 
The area that subsided included the northern 
and western parts of Prince William Sound, 
the western segment of the Chugach Mountains, 
portions of the lowlands north of them, most 
of the Kenai Peninsula, and almost all of the 
Kodiak Island group. This area of subsidence 
covers approximately 110,000 km 2 , and is 
800 km long and 150 km wide. Plafker (1965) 
estimates that the volume of crust that has been 
depressed below its pre-earthquake level is about 
115 km 3 . 
The seaward limits of the earthquake and the 
tsunami-generating area were determined by 
means of a series of refraction diagrams based 
on Snell’s Law of Refraction using the velocity 
equation for shallow water waves, C = \/gd. 
Such a method of preparing refraction diagrams 
has shown good results, especially if carried out 
on large-scale charts with detailed bathymetry 
(Johnson, O’Brien, and Isaacs, 1948). 
In constructing the refraction diagrams for 
the Alaska tsunami, the marigrams of different 
tide gauge stations around the Pacific were con- 
sulted and the total travel time of the first wave 
at each station was determined. Then refraction 
diagrams were constructed toward the earth- 
quake area from each tide gauge station in 
lengths of time equal to the calculated travel 
time for that station. It was assumed that the 
last wave front in each refraction diagram would 
correspond to a point on the boundary of the 
generating area, and if enough refracted wave 
fronts from different stations were plotted, an 
envelope defining the tsunami-generating area 
could be drawn. 
Wave fronts were refracted from Yakatat, 
Cape Yakataga, Seward, Uzinki, Kodiak, Old 
Harbor, Unalaska, Adak, Attu, and Honolulu. 
The last front of each of the refracted waves is 
shown by a heavy dashed line in Figure 1. The 
seaward boundary of the generating area is near 
the 200-m depth contour which defines the edge 
of the continental shelf. Maximum displacement 
of the ocean floor occurred along the continental 
shelf, from an area southeast of Kodiak Island, 
to an area close to Cape St. Elias south of the 
island of Kayak (Fig. 1). Geologic evidence, 
however, has shown positive land displacements 
as far north as Cape Suckling and as far east 
as the Bering Glacier. It is quite probable, there- 
fore, that the tsunami-generating area extended 
farther to the northeast, although waves gener- 
ated in such shallow water would reach tide 
gauges much later and their origin would not 
be identifiable. 
Unfortunately, this same wave refraction tech- 
nique could not be used to define the northern 
and western boundaries of the main tsunami- 
generating area, because conditions in Prince 
William Sound and elsewhere along the coast 
of Alaska were further complicated by local 
tsunamis, oscillations, and surge. In addition, 
no tide gauge stations were operating in the 
area, and personal accounts were conflicting as 
to arrival times of the different waves. 
The northward limit is assumed to be re- 
stricted by the land boundaries, and the western 
