Point where maximum runup was UU feet above MLLW. It has been estimated 

 that tsunami damage at Seward exceeded $1^ million; the death toll was 

 12 persons, most of whom were in small boats in the boat harbor at the 

 time of the earthquake. 



5. Effects of the Main Tsunami and of Local Seismic Sea Waves 

 in Prince William Sound 



Prince William Sound is an almost land-locked embayment with 

 a grotesquely contorted coastline comprising deep fjords and bays and 

 innumerable islands. Its gross shape is triangular (Figure 157), and its 

 natural periods of oscillation probably approximate the values of Equa- 

 tion (U7) (p. 2U7 ) . Its fundamental mode period of 1.8 hours would make 

 it responsive to the main tsunami despite an expected high damping effect 

 from its greatly indented coastline. 



General uplift of the Sound during the earthquake occurred in the 

 form of a tilt in a northwest direction on a hinge at about 2/3 of the 

 distance from the mouth to the apex. The water surface may be assumed to 

 have followed this sudden tilt fairly closely, and set in motion a compli- 

 cated system of seiches. On this would have been impressed the tsunami 

 from the Continental Shelf with rather limited access through the island 

 straits. Experience of harbor surging phenomena suggests that the Con- 

 tinental Shelf oscillation could have successfully pumped and sustained 

 the seiches in the Sound. 



Because of its deep fjords and its proximity to the earthquake 

 epicenter, Prince William Sound experienced numerous slides whose wave 

 effects added to the general complexity of water movements. At many 

 places it would seem that the pattern of waves was similar to the pattern 

 at Seward (see Figure 159)- 



The Indian village of Chenega, on Chenega Island in Knight Island 

 Passage, was almost totally destroyed. Sea waves, striking during the 

 earthquake, killed 25 persons. Powerful initial damage from slide- 

 generated waves of relatively short period (3 to 5 minutes) occurred 

 at Whittier and Valdez. 



The case of Valdez is the best documented in the Prince William 

 Sound area. Valdez, with a population of about 60O, has a location at 

 the head of Port Valdez and Valdez Arm, a long embayment within the 

 Sound which, like Resurrection Bay, forms effectively a chain of three 

 basins, whose periods of free oscillation, as a group, approximate the 

 values given in Equation (^8) (p. 25^/. However, the last link in the 

 chain. Port Valdez, is virtually a closed basin and because of the nar- 

 row throat and elbow bend of the adjoining link (Valdez Narrows) is 

 considered to be fully capable of responding to its own modes of free 

 oscillation in the longitudinal direction. These periods, to the second 

 mode, are given by Equation (^9) (p. 255 )■ It is noteworthy that the 

 first mode period of I8 minutes for the latter agrees closely with the 



358 



