Waves 



125 



Loi /{h^eits fiariutr' 

 Beffh nf 

 Mdi-ck 16, If 3 2 



Figure 112. Part of tide curve for March 10, 1933, at San Pedro. Note small (approximately 6-inch) seiche having a 

 period of about 1 hour. The Long Beach earthquake failed to produce a tsunami or to materially disturb the seiche, 

 although it shook the gauge. Courtesy C. K. Green, U. S. Coast and Geodetic Survey. 



ported. If the disturbance happens to have 

 the same period as the seiche, resonance 

 builds up the amphtude so that waves in a 

 bay may be higher than those outside it, 

 even though wind waves cannot enter the 

 bay. An outstanding example is the Bay of 

 Fundy at Nova Scotia with its 16-meter 

 seiche of tidal period (Marmer, 1926, pp. 

 217-226). 



As an experiment for a class in oceano- 

 graphy, Rich (1956) measured the water level 

 at two stations in Los Angeles Harbor (A-1 

 and A-2) at 2- and 3-minute intervals for 

 6 hours during high tide on December 22, 

 1955. Additional data from three tide gauge 

 records were made available by the U. S. 



Coast and Geodetic Survey and the Los 

 Angeles Harbor Department. Comparison 

 of all records shows that the maximum seiche 

 amplitude of 1 1 cm occurred at the two sta- 

 tions farthest from the harbor entrance. 

 Station A-2 and Berth 174. The mean am- 

 plitudes present a regular decrease from 8 cm 

 at Station A-2 to zero at the lighthouse (Table 

 8). Irregularities in the record from the light- 

 house and in some of those at Berth 60 are 

 ascribed to wakes of passing ships. The 

 mean period for the three stations where it 

 could be measured reliably was 49.9 minutes, 

 in good agreement with the theoretical value 

 of 53 minutes, based on an average depth of 

 10 meters and basin length of 8200 meters 



