THE CALIFORNIA EARTHQUAKE OF APRIL 18, 1906. 
INTRODUCTION. 
On the morning of April 18, 1906, the coastal region of Middle California was shaken 
by an earthquake of unusual severity. ‘The time of the shock and its duration varied 
slightly in different localities, depending upon their position with reference to the seat 
of the disturbance in the earth’s crust; but in general the time of the occurrence may 
be stated to be 5" 12 a. m. Pacific standard time, or the time of the meridian of longi- 
tude 120° west of Greenwich; and the sensible duration of the shock was about one 
minute. 
The shock was violent in the region about the Bay of San Francisco, and with few 
exceptions inspired all who felt it with alarm and consternation. In the cities many 
people were injured or killed, and in some cases persons became mentally deranged, as 
a result of the disasters which immediately ensued from the commotion of the earth. 
The manifestations of the earthquake were numerous and varied. It resulted in the 
general awakening of all people asleep, and many were thrown from their beds. In the 
zone of maximum disturbance persons who were awake and attending to their affairs 
were in many cases thrown to the ground. Many persons heard rumbling sounds imme- 
diately before feeling the shock. Some who were in the fields report having seen the 
violent swaying of trees so that their top branches seemed to touch the ground, and others 
saw the passage of undulations of the soil. Several cases are reported in which persons 
suffered from nausea as a result of the swaying of the ground. Many cattle were thrown 
to the ground, and in some instances horses with riders in the saddle were similarly 
thrown. Animals in general seem to have been affected with terror. 
In the inanimate world the most common and characteristic effects were the rattling 
of windows, the swaying of doors, and the rocking and shaking of houses. Pendant 
fixtures were caused to swing to and fro or in more or less elliptical orbits. Pendulum 
clocks were stopt. Furniture and other loose objects in rooms were suddenly displaced. 
Brick chimneys fell very generally. Buildings were in many instances partially or 
completely wrecked; others were shifted on their foundations without being otherwise 
seriously damaged. Water or milk in vessels was very commonly caused to slop over or 
to be wholly thrown from the vessel. Many water-tanks were thrown to the ground. 
Springs were affected either temporarily or permanently, some being diminished, others 
increased in flow. Landslides were caused on steep slopes, and on the bottom lands of 
the streams the soft alluvium was in many places caused to crack and to lurch, pro- 
ducing often very considerable deformations of the surface. This deformation of the 
soil was an important cause of damage and wreckage of buildings situated in such tracts. 
Railway tracks were buckled and broken. In timbered areas in the zone of maximum 
disturbance many large trees were thrown to the ground and in some cases they were 
snapt off above the ground. 
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