the quay walls and piers, coupled with the use of well-secured, shock- 

 absorbing, floating fenders. A second stipulation might be that ships 

 of large size, permitted to berth, be equipped with automatic constant 

 tensioning, high-capacity, deck winches capable of ensuring taut moorings 

 at all stages of the tide or water level. Ships above a certain tonnage, 

 not meeting port requirements in this regard, could be compelled by 

 regulation to anchor in the roadstead outside the harbor, to specially 

 designed clump and groundline anchorages marked by permanent surface 

 buoys. Under normal sea conditions the dead weight of the clump resting 

 on the seabed would be a sufficient anchor for holding a ship in the 

 exposed roadstead. Under high sea or tsunami conditions, however, the 

 additional force imposed on the anchor line would lift the clump and 

 bring into action the ground line and true anchor, and thus cushion the 

 strain of severe drag while maintaining a small angle of inclination of 

 the ground line at the anchor and so preserving its holding power (see 

 also Wiegel, 1965). Such berthings would obviously require barge and 

 lighterage operations with attendant higher port charges for ship owners , 

 who would thereby be induced to equip their vessels with regulation 

 winch machinery to gain the facility of protected harbor berthings. 



In small-boat basins, landing floats and platforms should be re- 

 quired to meet particularly stringent specifications ensuring more robust 

 equipment than is normally required of marinas, not subject to tsunami 

 attack. In particular, vertical guide piles could be interconnected at 

 an appropriate overhead level by longitudinal, cross and diagonal bracings, 

 so that loads are transmitted to the equivalent of a large framed struc- 

 ture rather than to single flexible piles. Small-boat lashings to the 

 floating docks should also be required to meet stringent specifications 

 for size and type, in keeping with the nature and size of the craft 

 moored. 



7. Economic Aspects of Protective Measures 



Standards of safety and economy that would apply in any given 

 coastal region having a potential for tsunami attack, will obviously 

 depend on a number of factors, such as: 



a. The degree to which the region is seismically active. 



b. The historically prevalent nature of earthquake faulting. 



c. The extent to which earthquakes occur seaward or landward 

 of the coastline. 



d. The statistical trend of focal depth of local earthquakes 

 in relation to distance from the coastline. 



e. The exposure of the coast to transocean tsunamis. 



f. The protection afforded by offshore islands. 



371 



