250 HOVEY— EARTHQUAKES : [April 24, 



5:12 o'clock A. M., western time, April 18, 1906, wrought ruin or 

 serious damage over a belt 50 miles wide and 300 miles long. The 

 approximate position of the epifocal point of the disturbance is 

 given by F. Omori as being in latitude 38° 15' N. and longitude 

 123° W., near Tomales Bay.^^ The horizontal shearing movement 

 varied from nine to twenty feet toward the N.N.W. or the S.S.E. ; 

 the vertical movement did not exceed two feet at any locality and 

 usually was absent, upthrow where present being on the west side 

 of the rift. Among the effects along the line of the fault were 

 rifting and bulging of the soil, ofifsetting of fences, roads and walks, 

 splitting and overturning of trees, landslides in the mountains, 

 wrecking of railway tunnels, spreading and telescoping of lines of 

 waterpipe. This is the most disastrous earthquake that has visited 

 the United States, though the chief destruction wrought was due to 

 the fire that followed in the train of the quake rather than to the 

 shock itself. About four hundred people are known to have lost 

 their lives in the catastrophe, and at least $350,000,000 worth of 

 buildings and other property were ruined by the shock or consumed 

 by the flames. An exact statement of the pecuniary loss caused by 

 the shock cannot be made, but the insurance companies finally agreed 

 upon a settlement to the eft"ect that one-fourth of the damage was 

 due to the earthquake and three-fourths to the fire, and this esti- 

 mate may be accepted as the best that can be made. More than 

 four square miles of the city of 400,000 inhabitants was devastated. 



The main part of San Francisco lies about eight miles northeast 

 of the fault line, and the propagation of the waves through the 

 city was in a direction N. 76° E., nearly normal to the fault line. 

 In general the advance of the wave motion on each side of the rift 

 was away from it. Omori concludes that both sides of the fault 

 line were displaced toward the N.N.W., the west side more than the 

 east, the amount of apparent slip being merely differential. In San 

 Francisco the chief damage was wrought upon structures built upon 

 alluvial or made ground. High steel-frame structures which were 

 not stiffly braced acted like inverted pendulums, causing ruin to 

 their walls. This was illustrated in the case of the City Hall in 

 San Francisco and the library buildings at Stanford University 



'^ " The California Earthquake of 1906," p. 289. 



