CHAPTER XXVIII

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.

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.

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."