THE EARTHQUAKE AND FIRE AND THEIR EFFECTS ON 
STRUCTURAL STEEL AND STEEL-FRAME BUILDINGS. 
By Frank Soul£. 
THE EARTHQUAKE. 
GEOLOGIC FEATURES. 
On the morning of April 18, 1906, central California experienced 
an earthquake, the most severe, as measured by its results, in the his- 
tory of the State. The seismograph in the observatory of the Uni- 
versity of California, at Berkeley, recorded the shock as beginning 
at 5 hours 12 minutes 6 seconds a. m., Pacific standard time, and as 
lasting for one minute and five seconds. Its severity was afterwards 
estimated and rated as IX in the Rossi-Forel scale of earthquake 
intensities. Other minor shocks followed immediately and at short 
intervals, so that before 7 p. m. of the same day thirty-one of these 
had been registered at the observatory. Slight shocks, coming suc- 
cessively after longer and longer intervals of time, were experienced 
during several weeks following, until finally the earth's crust in Cali- 
fornia seemed to have readjusted itself to new conditions of pressure 
and equilibrium. The material damage from the earth tremors was 
inflicted by the first great shock. The- minor ones following wrought 
no injury, except to throw down a few tottering walls that had been 
racked by the original earthquake. 
For many years the leading geologists in California have known 
that a rift, or line of dislocation in the earth's crust — called in com- 
mon parlance an "earthquake crack" — starting near Point Arena. 
extends in a straight line, at least 400 miles in length, in a direction 
S. 35° E. (fig. 1, p. 3). Passing under the ocean bed 8 miles west 
of the Golden (late, the rift cuts the shore again at Mussel Rock, runs 
along the reservoir basins of the Spring Valley Water Company and 
over the Coast Range of mountains, ignoring surface topography in 
its course, and extends at least to Mount Pinos, in Ventura County, 
and probably still farther to Lake Elsinore, in southern California. 
This great " fault " gives abundant geologic evidence of having been, 
in the remote past, the locus of many distinct earthquake movements 
and disturbances. 
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