40 U. S. COAST AND GEODETIC SURVEY 
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Fig. 18.—Tide curve, San Francisco, Calif., showing seiches due to changes in barometric pressure. 
1925. Seiches are evident on the curve for January 1, but are especially marked on 
the 2d, between 11 a.m. and 12 p.m. On that day the wind blew from the northeast 
with velocities up to 78 miles per hour. 
The Atlantic City tide gage is located about 1,500 feet from shore, on a pier that 
juts out into the open sea. The seiches must therefore represent oscillations of some 
part of a wide embayment of the coast. 
Figure 20 is an example of seiches due to a seaquake. On April 1, 1946 at 12" 29™ 
p. m., Greenwich civil time, a seaquake occurred in the North Pacific Ocean, about 
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Fic. 19.—Tide curve, Atlantic City, N. J., showing seiches due to heavy winds. 
