g. The peculiarities of the coastline to concentrate tsunami 

 energy in specific places. 



h. The resonating capacity of particular bays and inlets to 

 amplify tsunami runup. 



i. The geological nature of the coastal area, particularly its 

 susceptibility to submarine landsliding, to compaction with 

 vibration, and to earth avalanches. 



j . The extent to which a large area may be prone to subsidence 

 during a local earthquake. 



When all these factors are taken into account, it is clear that com- 

 pletely different standards of safety are likely to prevail in different 

 regions. As compared with Alaska, for example, California would appear 

 to be rather favored, particularly Southern California, which, for the 

 most part, is protected by offshore islands, and historically is not 

 particularly prone to local tsunami generation. 



There is as yet no hard and fast rule for determining a safety 

 standard. The lessons of the Alaskan earthquake of 196^+ emphasize the 

 need for secure foundations for waterfront structures, but in the presence 

 of total land subsidence, even the best of foundations cannot necessarily 

 ensure safety either for the structure it bears or for the people that 

 occupy the structure. 



Generally, if subsidence is not a problem, then real safety begins 

 with the placing of all structures on good foundations at a level above 

 the design runup. Such a measure may be impossible in a practical sense, 

 particularly when waterfront facilities are involved and land levels are 

 low. It may then be necessary to resort to some sort of protective works 

 as are currently being considered for Hilo in Hawaii. The question of 

 economy is then directly involved. Assuming that tsunami warning services 

 can ensure safety of human life, at what stage does it become economic to 

 resort to total or partial protection of the assets of a seaside community 

 by such measures as special breakwaters, barriers, seawalls, dikes, 

 plantations of trees, or shelter buildings? There are at present no 

 general answers, except to say that each area seeking immunity from 

 tsunami attack must be separately and carefully investigated. 



372 



