44 WARREN UPHAM, M.A._, D.SC.^ F.G.S.A.^ ON THE SAN FRANCISCO 



many during the next three days in escaping from the wide 

 devastation of fire, are so fresh in the memories of those who 

 were there, and of all who have read the accounts given in 

 newspapers, magazines, and books already published, narrating 

 and portraying the awful events and scenes, that they need not 

 be again recited. In this paper attention will be directed 

 mainly to geological description and explanation, so far as can 

 be determined, of the causes of these two earthquakes, which 

 came so near together, bringing ruin temporarily to the fairest 

 and most prosperous cities on the Pacific coast of both the 

 northern and southern American continents. 



The first and greatest shock in San Francisco and the 

 contiguous country had a duration of one minute and 

 five seconds, as recorded at the observatory of the State 

 University in Berkeley. It was followed within an hour by 

 twelve minor shocks. During the same day the number of the 

 secondary shocks was thirty-one ; and they continued for many 

 days, generally diminishing in frequency and intensity, as is 

 the usual history of great earthquakes. The ensuing minor 

 shocks are due to secondary adjustments of the faulted rocks 

 after the principal fractures and slips have relieved, almost 

 instantaneously, the greater part of the stress which was pent 

 up and growing through many years. 



An area about 400 miles loncj from north to south and 

 averaging iifty miles iu width displayed in more or less degree 

 the destructive effects of this earthquake. Its tremors were 

 shghtly felt much farther, from Coos bay in Oregon south to 

 Los Angeles, and eastward across California into Nevada, 

 being especially notaljle along the eastern flank of the Sierra 

 Nevada. 



To much greater distances, and indeed all the way around 

 the world, the rock waves or vibrations ran rapidly and were 

 recorded by the seismographs of observatories. Particularly 

 important records of this paroxysm were thus obtained at 

 Tokyo in Japan and at Potsdam in Germany. 



Marvellous speed of transmission of the earth tremors or 

 waves, similar to that ascertained in the case of the Charleston 

 earthquake in 188G, was shown by the time of observations in 

 Washington, ]).C., and in Sitka, Alaska. Professor C. F. Marvin, 

 of the United States Weather lUireau, writes of the transmission 

 of the earth vibrations to the city of Washington : 



" The great circle distance from San Francisco to Washington is 

 about 2,4'}5 miles, whereas the distance tln-ougli the crust is about 

 40 miles shorter, and the straightdine path cuts below the surface 



