deep-ocean form of the tsunami. Therefore, a means of recording tsunamis 

 in the open ocean is needed. 



Vitousek (1961) proposed placing permanent instrument packages in 

 the ocean, connected to abandoned transpacific telegraph cables. A 

 system of this type would provide deep-ocean data, and would also provide 

 additional useful information for the Tsunami Warning System because of 

 the direct connection with the gage. However, Vitousek and Miller (1970) 

 indicate that cable-connected systems would be expensive, and that the 

 cost of laying special cables would be unrealistic. 



Vitousek and Miller discuss four possible methods of measuring a 

 tsunami in the open ocean: (a) Free-drop recoverable instrument package, 

 (b) an undership instrument, (c) an underbuoy instrument, and (d) the 

 cable-connected instrument previously discussed by Vitousek. Shinmoto 

 and Vitousek (1978) give details of an air-deployable free-drop tsunami 

 gage which can be emplaced quickly after a tsunami occurs. 



While some deployment of open-ocean gages has been carried out, 

 experience in operating such gages is limited. Future use of such gages 

 is required to determine their practicality and reliability as part of 

 the Tsunami Warning System, and to obtain open-ocean tsunami data. 



IX. SUMMARY AND CONCLUSIONS 



The potentially high value of property in the coastal zone and the 

 intensive development of such land for both private and public use 

 require that careful consideration be given to the possibility of cata- 

 strophic flooding of areas of the coastal zone, in or near seismologi- 

 cally active regions, by tsunamis. Small variations in predicted flood 

 levels may affect property worth millions of dollars, and may have 

 substantial effects on flood insurance premiums and permits for utiliza- 

 tion of property, so it is necessary to have as high a degree of accuracy 

 as possible in defining flood zones, e.g., the 100-year flood level. 

 Also, large powerplants are typically located at low elevations because 

 of pumping requirements for cooling water, and port facilities are neces- 

 sarily located near the shoreline, so that well-designed protection is 

 required for high-cost facilities. 



Available data on tsunami inundation come from visual observations 

 (including posttsunami surveys) and from tide gage records. Data are 

 generally only available for a few occurrences, and only at specific 

 coastal areas. Some data can be obtained from historical accounts, but 

 such data are dependent on incomplete personal observations, usually by 

 untrained observers. Open-ocean data on tsunamis, needed for verification 

 of numerical investigations, are almost nonexistent. 



Numerical data are used to supplement the available field data on 

 tsunami flood levels. Numerical procedures have been developed that 

 allow the simulation of a tsunami source, the generation and propagation 

 of the tsunami waves across the ocean, and the interaction of the tsunami 

 and coastal topography. Procedures have also been developed to simulate 

 tsunami flooding shoreward of the coastline. The numerical results, which 

 are compared to the more limited field measurements for verification, 



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