Selected American history

CHAPTER XIV.

The Earthquake Wave Felt Round the Earth.

The outbreak of earth forces at San Francisco did not stand alone. There were others elsewhere at nearly the same time, the whole seeming to indicate a general disturbance in the interior of the earth's crust. Some scientists, indeed, declared that no possible connection could exist between the eruption of Mount Vesuvius and the earthquake at San Francisco, but others were inclined to view certain facts in regard to recent seismic and volcanic activity as, to say the least, suggestive.

As to the actual cause of the California earthquake, the wisest confession we can make is that of ignorance, there being almost as little known as to the origin, period and coming of earthquakes as when Pliny wrote 1,800 years ago. The Roman observer knew that the tremor passed like a wave through the surface of the earth; he knew that it had a given direction, and he knew that certain regions were rife with seismic disturbance. More he could not say, and when this is said all has been said that is known to-day.

Setting aside these general considerations, let us return to the question of the disaster at San Francisco on that fatal morning of April 18th. The shock did not come unexpectedly. A month previous there had been a severe earthquake in the Island of Formosa, and many lives were lost there, while an enormous amount of damage was done. Only a few days before the event in San Francisco there was another earthquake in the same island. Still greater havoc was caused by it than by the earthquake in March, but fewer lives were lost, the reason being that the people were warned in time. Early in April the eruption of Mount Vesuvius reached its height and devastated the country around the volcano, covering an enormous territory with ashes, and caused the loss of hundreds of lives.

On Tuesday night, April 17th, word was received from Piatigorsk, Circassia, that there had been two severe earthquake shocks the previous day in Northern Caucasia. The same night a telegram from Madrid said that the newspapers there reported that the long-dormant volcano on Palma, the largest of the Canary Islands, was showing signs of eruption, columns of smoke issuing from the crater.

While scientists as a rule doubt that there was any connection between these volcanic phenomena and the earthquake at San Francisco, yet reports from the Mount Weather observation station in Virginia, a few miles from Washington, show that the eruptions of Vesuvius acted on the magnetic instruments by electro-magnetic waves in such a way as to disturb the electrical potentials at that place. Be this as it may, there is one remarkable circumstance in regard to all this activity. All the places mentioned—Formosa, Southern Italy, Caucasia, and the Canary Islands—lie within a belt bounded by lines a little north of the fortieth parallel and a little south of the thirtieth parallel. San Francisco is just south of the fortieth parallel, while Naples is just north of it. The latitude of Calabria, where the terrible earthquakes occurred in 1905, is the same as that of the territory affected by the recent earthquake in the United States. This may or may not have some bearing on the question.

Whatever be thought of all this, one thing is certain, the earthquake which laid San Francisco in ruins was felt the world over, wherever there were instruments in position to detect and record it. The seismograph in the government observatory at Washington showed that the first wave, on April 18th, came at 8.19—equivalent to 5.19 at San Francisco; that at 8.25 there was a stronger wave motion, and that from 8.32 to 8.35 the recording pen was carried off the paper. The vibrations did not entirely cease until 12.35 P. M., during this period there having been nearly half an inch of to and fro motion in the surface of the earth.

From far away New Zealand, on the same date, the government seismograph at the capital, Wellington, recorded seismic waves that apparently passed round the earth five times at intervals of about four hours each.

Across the Atlantic, at Heidelberg, in Germany, the records showed vibrations lasting one hour. At Sarayevo, in Bosnia, there was a sharp shock at 11 A. M., undulating from west to east. At Funfkirchen, in Hungary, at Laibach, in Austria, in the Isle of Wight, off the coast of England, and all through Italy, from north to south, the shocks were felt.

At Hancock, Mich., a shock was felt on April 19th a mile below the surface in the Quincy mine of such severity that one man was killed and four injured by a fall of rock loosened by the trembling of the earth. There is no evidence, however, that this had any connection with the California disaster, the dates not coinciding.

Turning to the Far East, across the Pacific, seismographs in the Imperial University of Tokio showed that the earthquake was felt there eleven minutes later than in San Francisco, and similar instruments in Manila detected the arrival of the seismic waves twenty minutes after the San Francisco shock. In this there was a slight difference in time compared with Tokio, but, considering the distance, near enough to prove that the disturbances came from the same source.

Not until the day following was any noticeable disturbance felt in Honolulu, but on April 19th shocks were plainly felt for six minutes and the water in the harbor rose rapidly. Panic seemed imminent just before the shocks subsided. While earthquakes are by no means infrequent in these islands, this was more severe than any recorded in recent years, causing buildings to sway to and fro and partly demolishing some of frail construction.

If, as the majority of men qualified to discuss earthquakes seem to think, the San Francisco earthquake had no connection with volcanic action, but was caused by what is technically known as a "fault" in the formation of the crust of the earth, it seems easy enough to account for these wave motions travelling round the earth. How widely this may really have made itself felt it is not possible to say. Several of the great earthquakes in Japan have been recorded in the seismographs of the observatories on every continent and in Australia, showing that in severe disturbances of this kind the whole surface strata quiver, alike under the oceans and over the continents and islands. At the time of a shock, of course, half of the world is in darkness and asleep. This is taken to account for the fact that so far only a few observatories have reported catching the San Francisco vibrations.

The instruments invented for the recording of the motions of the earth's crust are looked upon by scientists as the most delicate of all machines. So highly sensitive are they, indeed, that the very slightest vibratory motion is recorded perfectly. Even the tread of feet cannot escape this instrument if sufficient to cause a vibration.

There are three classes of instruments for the automatic recording of earth tremors, each with its own particular function. First is the seismoscope, which will merely detect and record the fact that there has been such a tremor. Some of these are so equipped as to indicate the time of the disturbance.

Second, is the seismometer, the function of which is to measure the maximum force of the shock, either with or without an indication of its direction. The third instrument is the seismograph, which is so arranged that it will accurately record the number, succession, direction, amplitude and period of successive oscillations. This last instrument is by far the most delicate of the three.

In the construction of this earthquake recording machine the maker must so suspend a heavy body that when its normal position is disturbed in the most infinitesimal degree no reactionary force will be developed tending to restore it to its original position. The inventor has never been found who could accomplish this suspension of a body to perfection. The seismograph of to-day, however, has reached a stage of perfection where close approximations are obtained in the records made.