THE SAN FRANCISCO EARTHQUAKE OF APRIL 18, 1906
About twelve minutes past five o'clock on the morning of the 18th of
April, 1906, the inhabitants of San Francisco were rudely awakened by
a few frightful earthquake shocks. Their houses were violently shaken
to and fro, and on all sides were heard the awful crashings of falling
walls, chimneys, and buildings, together with the death-shrieks of
those caught in the ruins. Rushing madly into the streets they could
see on every side evidences of destruction; for, in almost every
direction, were heaps of fallen buildings, still being violently
shaken by the earthquake waves that rapidly passed through the solid
earth. Huge cracks or crevices had been formed in the streets, while
the heavy rails of the trolley tracks had been bent and twisted by the
mighty forces.
Before describing in detail the great San Francisco earthquake, the
location of the city and its surroundings demand consideration.
As can be seen from the map, Fig. 47, San Francisco is situated on the
western coast of California, at the northern end of a peninsula, some
twenty miles in length and about six miles in width. This peninsula
is formed by the magnificent Bay of San Francisco on the east, a
navigable strait called the Golden Gate on the north, and the Pacific
Ocean on the west.
[Illustration: FIG. 47. MAP OF WESTERN COAST OF CALIFORNIA SHOWING
POSITION OF SAN FRANCISCO]
San Francisco Bay, accessible by the Golden Gate, is the principal
harbor on the Pacific Coast, and is, indeed, one of the most
magnificent harbors in the world. It is land-locked, that is,
surrounded by a continuous land border except at its entrance through
the Golden Gate. Including San Pablo Bay, it has a length of about
fifty-five miles, and varies in breadth from three to twelve miles.
The entrance to the harbor, however, is impeded by a bar across the
mouth of the Golden Gate, over which there is a depth of but thirty
feet of water at low tide.
San Francisco has over 750 miles of streets, 200 miles of which are
paved. The city is lighted by both electricity and gas, and has an
extensive system of water-works, the water being brought from the
Pilarcitos and Calaveras Creeks, situated from twenty to forty miles
respectively from the city.
San Francisco is in a region where earthquakes are common. It might,
therefore, be visited at any time by a great catastrophe. There have
occurred between 1850 and 1888, no less than 254 earthquake shocks in
the State of California, these shocks having been especially frequent
in the country surrounding San Francisco Bay. The most severe were
the earthquake of 1868, which injured San Francisco; the Owens Valley
earthquake of 1872; the Vacaville earthquake of 1892; the Mare Island
earthquake of 1898; and a smaller earthquake in 1900. Since 1900 there
was a period of rest until the 18th of April, 1906.
As in the case of practically all severe earthquakes, that which
destroyed San Francisco consisted of a few momentary shocks: then all
was over. According to a preliminary report of the State Earthquake
Commission, appointed by the Governor of California, April 21st, 1906,
these shocks, as recorded in the observatory at Berkeley, began at
twelve minutes and six seconds after five A. M., Pacific
Standard Time. Their entire duration was only one minute and fifty
seconds, but, as frequently happens, there were a number of minor
shocks, following at regular intervals during the next few hours as
well as the next few days.
While the most severe shocks were in the neighborhood of the Peninsula
of San Francisco, yet minor disturbances were felt as far north
as Coos Bay, Oregon, and as far south as Los Angeles, California.
As shown by recording instruments at the seismograph station at
Washington, D. C., Sitka, Alaska; Potsdam, Germany; and Tokio, Japan,
a series of waves were propagated through the earth, as well as over
its periphery.
The damage done within the city limits was wide-reaching. Among the
buildings almost completely destroyed were the City Hall, on which
about $7,000,000 had been expended, the United States Post Office,
besides many business blocks, hotels, department stores, theatres,
banks, churches, and dwelling houses.
Amid the terrors of such a calamity it is difficult to obtain
observations possessing any scientific value. Fortunately, however,
there was in the city a physicist trained to observe phenomena of this
character, Professor George Davidson of the University of California.
Like others, he had been awakened by the first severe shock. At once
recognizing the nature of the phenomenon, and desirous of obtaining
the exact time of its occurrence, he counted seconds while he ran
towards the table on which he had placed his watch, and in this way
estimated that the shock occurred at twelve minutes past five in
the morning. The closeness of this observation is emphasized by the
fact that it differed from the recorded time by only six seconds. He
states that the motion, at the time of its greatest intensity, closely
resembled that of a rat vigorously shaken by a terrier.
The destruction caused by the earthquake was, however, but a small
part of the total loss to the city. Fires were almost immediately
started in the ruined houses by the fires in the kitchens and other
parts of the houses, by the ignited jets of the illuminating gas,
and, perhaps, especially, by the crossing of numerous electric light
wires.
The manner in which the woodwork and other combustible materials of
the buildings were loosely tossed together by the shocks helped the
quick spread of the fires, and this, too, was probably greatly aided
by the illuminating gas from the broken gas pipes and mains. Eight
severe conflagrations were, therefore, soon raging in different parts
of the doomed city. What made these fires especially dangerous was the
fact that the earthquake shocks had destroyed the water pipes. Thus
the firemen were handicapped in their heroic endeavors to extinguish
the flames.
At the time of the fire a strong wind was blowing from the northeast.
Since the firemen were unable to check the flames, the fire line
rapidly advanced. Its path led towards the best residential parts of
the city through portions of the mission section containing a dense
population of poor people. The dwellings in this latter section
consisted of frame houses, through which the flames rapidly spread.
There was but one way to save the city from total destruction--a free
use of dynamite! This was intelligently employed until the supply gave
out, when it seemed that the city was doomed to utter destruction.
But at the last moment, as it were, came a lucky change in the
direction of the wind. Instead of blowing from the northeast, the
steady southwest winds set in, and beat back the fire on itself, so by
Friday, the 18th being Wednesday, it was under complete control and
the rest of the city was saved.
[Illustration: A SAN FRANCISCO PAVEMENT TORN BY THE
EARTHQUAKE _From a Stereograph, Copyright, 1906, by Underwood &
Underwood_]
The extent of the fire is thus described in an article in the
"Outlook," for Saturday, April 28th, 1906, as follows:
"The turn in the direction of the fire endangered for a
time the great Ferry House, at the foot of Market Street.
While the section actually destroyed is not, geographically
speaking, much more than one-third of the city limits,
yet it is in the heart of San Francisco, and includes the
chief business streets and the Mission District, inhabited
by poor people, and a large part of the so-called Nob Hill
Quarter, where were the finest and costliest residences of
the city. Another fine residence section, Civic Heights,
escaped, together with that known as the Western District.
"The unburned district, though large in extent, was in
the nature of suburbs, and was not closely built up, so
that estimates made, as late as Saturday, declared that
three-fourths of San Francisco's improvements in real
estate had been destroyed."
The burnt district was about two miles from east to west and from two
to four miles from north to south, with, of course, very irregular
outlines.
Naturally, the great destruction wrought by the earthquake of April
18th, 1906, attracted the almost universal attention of scientific men
especially interested in earthquake phenomena. We are, therefore, able
to speak authoritatively about the probable causes.
The great San Francisco earthquake of April 18th, 1906, appears to
have been a _tectonic_ quake. Ransome, in an article entitled, "The
Probable Cause of the San Francisco Earthquake," says:
"The region thus amply fulfils the conditions under which
tectonic earthquakes arise. It is in unstable equilibrium,
and it is cut by long northwest faults into narrow blocks
which are in turn traversed by many minor dislocations.
Under the operation of the unknown forces of elevation and
subsidence, stresses are set up which finally overcome the
adhesion of the opposing walls of one or more of the fault
fissures; an abrupt slip of a few inches, or a few feet,
takes place and an earthquake results. The region extending
for some hundreds of miles north and south of the Bay of
San Francisco may be considered as particularly susceptible
to shocks on account of the number and magnitude of the
faults and the evidences that these furnish of very recent
slippings and the marked subsidence in the vicinity of the
Golden Gate."