The untreated timber decking shows considerable deterioration, and a 

 deck timber replacement program is currently in progress. 



The cathodic protection system installed by Richfield is working 

 well, and the steel piles are in good condition, even though marine life 

 has stripped some of the coal tar enamel at the bottom line. 



The concrete abutment cap, the only concrete in the causeway contract, 

 has become an example of the need for good concrete specifications and 

 their rigid enforcement in a marine environment. Concrete specifications 

 for the island contract and the causeway contract were similar. Concrete 

 testing for the causeway was infrequent, since so little work was involved; 

 the island concrete was carefully controlled. The cause way abutment con- 

 crete now shows considerable crazing typical of alkali-aggregate reacti- 

 vity; all concrete placed on the island is in excellent condition. 



14. Seismic Evaluation 



Earthquake safety was a critical consideration during the design. 

 It was recognized that damage to the island from seismic events could 

 result from four causes: slope failure of the revetments, liquefaction of 

 the sand core, flooding of the island from earthquake-generated tsunamis, 

 or area subsidence due to tectonic fault movement. 



The slope stability of the island revetments required for resistance 

 to wave action was judged adequate against slope failure from earthquakes. 



Liquefaction of the sand core was difficult to evaluate because lique- 

 faction risk and phenomena were not then so well recognized as today. Al- 

 though compaction of the sand would have essentially eliminated the risk 

 of liquefaction, the cost of compacting the underwater part of the core 

 fill would have added about 10 percent to the estimated island cost, so the 

 final design called for high compaction of only the part of the core above 

 water. 



The possibilities of tsunamis and area subsidence from earthquakes are 

 related -- both phenomena are usually generated by vertical block movements 

 during fault-associated earthquakes. The Santa Barbara Channel area has not 

 shown the susceptibility to damage from distant tsunamis that a few critical 

 areas show, so the prime concern was for locally generated tsunamis. Recent 

 San Andreas and most California fault movements have been primarily horizon- 

 tal rather than vertical and the probability of a large locally generated 

 tsunami appears very low. Placing the island work level about 10 feet above 

 the mean higher high water level was primarily based on wave action require- 

 ments, but this was also considered reasonable protection against tsunamis 

 or sudden area subsidence from earthquakes. 



As part of a current seismic evaluation of the island, the seismicity 

 of the area was studied. Figure 16 shows all earthquake epicenters within 

 100 miles of the island above magnitude 4.5 that occurred in the 42 years 

 from 1930 to 1972. Also noted are the most recent earthquake felt at the 



53 



