THE subterranean movement that caused the earthquake at San Francisco was felt in greater or less degree at many distant places on the earth’s surface. The scientists in the government bureaus at Washington believe that the subterranean land slide may have taken place in the earthquake belt in the South American region or under the bed of the Pacific Ocean. San Francisco got the result of the wave as it struck the continent, and almost simultaneously the instruments in Washington reported a decided tremor of the earth, and the oscillations of the needle continued until about noon.
At the weather bureau the needle was taken from the pivot and had to be replaced before the record could be continued. Other government stations throughout the country also noted the earthquake shock, and they agree in a general way that the disturbance began according to the record of the seismograph at nineteen minutes and twenty seconds after 8 o’clock. This would be the same number of minutes and seconds after 5 o’clock at San Francisco, which accords entirely with the time of the disaster on the Pacific Coast.
There seems to be no reason to believe the earthquake shock in San Francisco had any direct connection with the eruption of Vesuvius. That eruption had been recorded from day today on the delicate instruments established by the weather bureau at the lofty station on Mount Weather, high up in the Virginia hills. This eruption of Vesuvius did not disturb the seismograph even at the period of great activity, but apparently Vesuvius and Mount Weather were like the lofty poles of two wireless telegraph stations, and between them there passed electrical magnetic waves encircling the earth. The records made at Mount Weather were of the most distinct character, but they showed disturbances in the air of a magnetic type and did not indicate any earthquake.
In explaining the San Francisco trembling, C. W. Hays, the director of geology in the geological survey, explained that earthquakes are, according to modern scientific theory, caused by subterranean land slides, the result of a readjustment as between the solid and the molten parts of the earth’s interior.
“The earth,” he said, “is in a condition of unstable equilibrium so far as its insides are concerned. ‘ The outer crust is solid, but after you get down sixty or seventy miles the rocks are nearly in a fluid condition owing to great pressure upon them. They flow to adjust themselves to changed conditions, but as the crust cools it condenses, hardens, and cracks, and occasionally the tremendous energy inside is manifested on the surface.
“When the semi-fluid rocks in the interior change their position there is a readjustment of the surface like the breaking up of ice in a river, and the grinding causes the earthquake shocks which are familiar in various parts of the world. The earthquake at San Francisco was probably local, although the center of the disturbance may have been thousands of miles away from that city.
Prof. Willis L. Moore, the chief of the weather bureau, in talking of the records of the earthquake in his department, said:
“We have a perfect record of this earthquake, although we are thousands of miles away from the actual tremor itself. There were premonitory tremblings, which began at 8:19 and continued until 8:23 or thereabout. Then there was severe shock which threw the pen off the cylinder.
“According to our observations here there was a to and fro motion of the earth in the vicinity of Washington amounting to about four-tenths of an inch at the time of its greatest oscillation. These movements kept up in a constantly decreasing ratio until nearly half an hour after noon.
“San Francisco may have been a long way away from the real earthquake and merely have been within the radius of severe action so as to produce disastrous results. It is quite likely, in fact, that the greatest disturbance may have taken place beneath the bed of the Pacific Ocean.
“If it resulted in an oscillation of the earth of only a few inches there would be no likelihood of a great tidal wave. If, however, there was produced a radical depression in the bed of the ocean, the sinking of an island, or some other extraordinary disturbance, a tidal wave along the Pacific Coast would almost certainly be one of the events of this great disaster.
“There are apparently three distinct weak spots in the United States, which are peculiarly subject to earthquake shocks, and we are likely sooner or later to hear from all of them in connection with the shock at San Francisco. There is one weak area along the southern Atlantic coast in the vicinity of Charleston, another is in Missouri, and the third includes the Pacific Coast from a point north of San Francisco down to and beyond San Diego.”
In describing the instruments at the weather bureau which make the record of earthquakes, even when the movement is so small that the ordinary person does not recognize it, Prof. Moore said:
“The apparatus we have is a pen drawing a continuous line on a cylinder which revolves once every hour and is worked continuously by clockwork in an exact record of time. It moves in a straight line when there is no disturbance, and it jumps from right to left and back again when there are serious oscillations of the earth. The extent of these movements of the pen measures the grade of the oscillation. You may think it is a fantastic statement, but this seismographic pen is adjusted so delicately that it will register your step in its vicinity.
“The instrument is mounted on a solid stone foundation and what it registers is the effect of your weight pressing upon the earth. It is easy to see, therefore, that the record we have obtained of this earthquake shows a few preliminary tremblings, which seem to be premonitions, for about four minutes, then a great crash which threw the pen off the cylinder and finally a period of nearly four hours, during which there were slight tremblings of the earth, this latter period marking the readjustment after the actual shock.”
Most of the scientists were inclined to believe that the boiling process in the interior of the earth, although it goes on continuously, is subject to periods of greater or less activity. This activity may be, however, purely local, according to the scientific theory, for otherwise there would be eruptions in all the active volcanoes of the earth at the same time, and there would be earthquakes in every one of the areas where there is liability to seismic disturbances.
One government scientist in discussing the San Francisco earthquake said : “If we could have been right here in the vicinity of Washington a few hundreds of thousands of millions of years ago, we should have seen earthquakes that were earth-quakes. The Alleghanies were broken up by great convulsions of the earth, and it is probable that this North American continent of ours was rocked a foot or two at a time, causing a tremendous crash of matter and the reorganization of the world itself.
“The crust, while not necessarily thinner, is not so solid. In cooling it has cracked and left fissures or caverns or jumbled strata of softer material between harder rocks, so that it is peculiarly subject to earthquakes.”
Maj. Clarence E. Thutton, U. S. A., retired, the most famous American expert on seismic disturbances, said it was probably the greatest earthquake that has occurred in this country since 1868. He declared that it undoubtedly would be followed by disturbances of less intensity in the same quarter. He stated most emphatically that the eruption of Vesuvius had no bearing whatsoever on the disturbance on the Pacific Coast.
J. Paul Goode, a professor in geology in the University of Chicago, attributes the cause of the Frisco earthquake to the Sierra Madre mountains, but not in a volcanic way, for he also claims that lava had nothing to do with the California shock. The shocks, he showed, can be attributed to mountains without volcanoes in their midst. The Sierra Madres are growing, he said, and for this reason they have shaken the city of San Francisco. He says that the gradual growing of mountains causes the under-lying blocks of the earth’s crust to slip up and down and shape the top of the earth in their vicinity when they fall any great distance.
His ideas upon the subject are: “I figure that the earthquake which caused so much damage in San Francisco came from what we call the focus of disturbance. This focus at San Francisco is seven miles below the surface of the earth. As the Sierra Madre mountains grow, a phenomenon which is constantly going on, the blocks of earth below change positions; as a large block falls a series of shocks travels, up and down much the same way as the rings in the water travel out from the point at which a pebble strikes. When the vibration reaches the surface crust a severe shaking of the country adjacent is the result.
“From the actions of the earth in April of 1892, when such a severe shock was felt in San Francisco, I have no doubt but that a second earthquake will follow closely upon the one of yesterday,- as the second followed the first in 1892.. In that year the first came upon the 19th of April and the second upon the 21st.”
Of 948 earthquake shocks that have been recorded in California previous to 1887, 417 were most active in San Francisco.
The seismographs which record the merest tremors and determine the place of the shock show that 344 have occurred since 1888. Half of the sum total have occurred in the vicinity of the gate city and for this reason it is believed that the severe shock of April 18 was the final fall of a crust of the earth which has been gradually slipping for centuries, causing from time to time the slight shocks.
The seismic physics of San Francisco and its immediate neighborhood have engaged the careful study of physical geographers. The commonly accepted opinion is one which was formulated by Prof. John La Conte, professor of geology in the University of California, and one of the world’s geological authorities. His ex-planation is based upon the mountain contours of the coast of California from the Santa Barbara channel northward to the Golden Gate. In this region are represented two peninsulas, one visible, the other to be discovered through examination of the altitudes upon the map corresponding to existing geological features. This second and greater peninsula comprises the Monte Diablo and Coast ranges, separated from the Sierra elevation by the alluvial soil of the low-lying valley of the San Joaquin. This valley is contoured by the level of 100 feet and lower for a considerable portion of its length, and practically all of it lies below the level of 500 feet. The partition thereby accomplished between the Sierra mountain mass and the coastal mountains is sufficiently pronounced to indicate what was at no remote period an ‘extensive peninsula.
This valley of the San Joaquin lies above the line of a geological fault, at a depth which can only be estimated as somewhere about a mile. The artesian well borings which have been abundantly prosecuted in the counties of Merced, Fresno, Kings and Kern afford evidence looking toward such a determination of bedrock depth. On the ocean side the continental shelf is extremely narrow. The great peninsula presents a most precipitous aspect toward the ocean basin. It is interrupted at intervals by deep submarine gorges extending close to the shore.
The oceanic basin of the Pacific is throughout a region of volcanic upheaval and seismic disturbance.
Conditioned on the one side by the known fault of the San Joaquin Valley and on the other by the volcanic activity of the Pacific basin, the greater peninsula of San Francisco in particular has always been subject, so far as the memory of white settlers can go, to frequent shocks of earthquake. In the last score or more of years seismographic observatories have been maintained at several points about San Francisco bay, and the records have been sufficiently studied to afford data for comprehension of the varied earth waves which have made themselves felt either to the perception of the citizens of the Golden Gate or to the sensitive instruments. Such observations have been conducted by Prof. George Davidson, for many years in charge of the Coast and Geodetic Survey upon the Pacific Coast; by Prof. Charles Burckhalter; of the Chabot Observatory, in Oakland, and by the staff of the Lick Observatory on Mount Hamilton.
Careful inspection of these records shows that two systems of earthquake disturbances act upon San Francisco. Those of the lighter series show a wave movement beginning in one of the easterly quadrants and more commonly in the southeastern. This series of light shocks is attributed to the slip along the line of the San Joaquin fault. While they may occur at any season of the year, they are more frequently observed when the San Joaquin river is running bank high under the influence of the melting snows in the foothills of the Sierra. That such a condition has recently existed is made clear by the report within less than a month of floods in the interior valleys of the State. Assuming, as the geologists do, that the fault in the valley lies near the roots of the Monte Diablo range, on the western edge of the alluvial plain, it will be seen that the physical factors involving the slip are very simple. There is a wide, flat plain bounded on the west by a line of weakness in the rock supports. When this plain is carrying an abnormal weight of water the tendency is to break downward at the line of the fault. This tendency will produce a jar in the mountain mass which will be rapidly communicated to its farthest extremity.
The earthquakes which have their origin in the disturbances to which the oceanic basin is subject always approach San Francisco from the direction of the southwest quadrant. These have been uniformly more violent than those whose origin is attributed to the San Joaquin fault. While the records of San Francisco earthquakes up to the present have exhibited a mild type, the damage to property having hitherto been slight, it would appear from the extent and violence of the present temblor that both causes had for once united.
The possibility of such simultaneous action of the two known seismic factors of the greater peninsula had been foreseen by Prof. Le Conte. He stated that if at any time an earthquake wave of only moderate violence should come in from the oceanic basin in sufficient strength to jar the coastal mountain masses at a period when the San Joaquin Valley was bearing its maximum weight of water the conditions would be ripe for simultaneous shocks from the southwest and from the southeast. In such a condition, while neither of the shocks by itself would be capable of doing any great amount of damage to buildings in San Francisco, the combination of two distinct sets of waves might prove too much for any work of man to withstand.
In spite of the declarations of some scientists that there can be no possible connection between the eruption of Mount Vesuvius and the earthquake of San Francisco, others are inclined to view certain facts in regard to recent seismic and volcanic activity as, to say the least, suggestive.
There is one very remarkable circumstance in regard to all this activity. All the places mentionedFormosa, Southern Italy, Caucasia and the Canary Islandslie 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 last year, is the same as that of the territory affected by yesterday’s earthquake in the United States.
There is another coincidence, which may be only a coincidence, but which is also suggestive. The last previous great eruption of Vesuvius was in 1872, and the same year saw the last previous earthquake California which caused loss of life.
Camille Flammarion expressed the opinion that the earth-quake at San Francisco and the eruption at Vesuvius are directly connected. He also sees a connection between the renewed activity of Popocateptl, Mexico’s well-known volcano, and the disturbance on the Western coast. He says that, though the surface of the earth is apparently calm, “there is no real equilibrium in the strata of the earth,” and that the extreme lateral pressure which is still forming mountains and volcanoes along the Western coast brought about an explosion of gases and the movement of super-heated steam several miles below San Francisco, resulting in an earthquake.
Another theory is that the earth in revolving is flattening at the poles and swelling at the equator, and the strata beneath the surface are shifting and sliding in an effort to accommodate themselves to the new position. Other scientists scout this idea, saying that earthquakes are not caused by the adjustment of the surface of the earth, but by jar and strain as the earth makes an effort to regain its true axis.
As regards the possible connection between volcanoes and earthquakes, it is known that a violent earthquake, whose shocks lasted several days, accompanied the eruption of Vesuvius in the year 79, when Pompeii and Herculaneum were destroyed. In 1755 thousands upon thousands of people lost their lives in the memorable earthquake at Lisbon, in Portugal. At the same time the warm springs of Teplitz, Bohemia, disappeared, later spouting forth again. In the same year an Iceland volcano broke forth, followed by an uprising and subsidence of the water of Loch Lomond in Scotland. The eruption of Vesuvius in 1872 was followed soon after by a serious earthquake in California.
Coming to the present year, it is noticed that the earthquake in the island of Formosa, in which 1,000 people lost their lives, was followed by the eruption of Vesuvius on April 8. Soon after came the second great shock in Formosa, in which there was an even greater loss of life.
Later there were two earthquake shocks in Caucasia. At the same time the news of this appeared there was a report of renewed activity on the part of a volcano in the Canary Isles, which had long been dormant. In the United States two volcanoes which have been regarded as extinct for more than a centuryMount Tacoma and Mount Rainier-began to emit smoke. In regard to Tacoma, Dr. W. J. Holland, head of the Carnegie Institute at Pittsburg, says: “There is no doubt that there has been a breakdown and shifting of strata, perhaps at a very great depth, in the region of San Francisco. There certainly is great connection between this earthquake and recent private reports which have come to me of intense volcanic activity on the part of Mount Tacoma.”
On the other hand, leading scientists contend that these in-stances are mere coincidences. “If there is any connection between Vesuvius and the Caucasus and Canary Isles earthquakes other places would have suffered too; New York, for instance, is on the same parallel,” says Prof. J. F, Kemp, of Columbia University.
Although each of these scientists has the most absolute faith in his theory, he really knows no more about the facts than any bey on the street. No one has ever descended into the interior of the earth and investigated the heart of a volcano but Jules Verne, and he only in his mind. What is needed now is exact information. The San Francisco catastrophe will teach many lessons, and among them the necessity for the close study of both volcanoes and earthquakes. There is no reason why earthquakes and other internal disturbances cannot be observed just as closely as the weather. In fact, it is entirely probable that the time will come when a seismological bureau will exist for the study of earthquakes, just as there is a Weather Bureau for observation of the weather, and it will be the business of its officials to prophesy and warn of approaching internal disturbances of the earth, just as the weather men announce the approach of bad weather. Government observation stations will be established, exact records will be kept, and in the course of time we shall learn exactly what earthquakes are and what are their causes.
Among other lessons that the disaster has taught is that the much-maligned skyscraper is about the safest building there is. Its steel-cage structure, with steel rods binding the stone to its wall, has stood the test and has not been found wanting. Of all the mighty buildings in San Francisco those of the most mod-ern structure alone survived. Their safety in the midst of collapsing buildings of mortar and brick argues well for like structures in other cities.
Mr. Otis Ashmore declared that the regions lying along the Pacific coast contain several of the moving strata which cause earthquakes. He said:
“While much concerning the origin of earthquakes is still a matter of doubt in the minds of scientific men, it is now generally conceded that the real cause is the sudden slipping and readjustment of the strata of rocks with the crest of the earth. As the earth is slowly cooling a very slow contraction of the earth’s crust is constantly going on, and as this crust consists very largely of stratified layers of rock, the enormous forces arising from this contraction are resisted by the solid rock.
“Notwithstanding the apparent irresistible nature of these layers of rock, they slowly yield to the enormous lateral pressure of contraction and gradually huge folds are pushed up in Iong mountain ranges. Usually this process goes on so slowly and gradually that the yielding of the rock masses takes place without noticeable jar, but occasionally a sudden slip occurs under the gigantic forces, and an earthquake is the result. This slip is usually only a few inches, but when two continents fall together for only a few inches enormous energy is developed.
“Such slips usually occur along the line of an old fissure previously formed, and the depth below the surface of the earth varies from one to twelve miles. Thus places situated near these old internal fissures are more likely to experience earthquakes than those farther away. It is a well known geological fact that the Pacific coast in California contains several of these fissures and earthquakes are more common there. The entire western part of the United States has been slowly rising for many centuries, and the shifting of soil due to erosion and transportation doubt-less contributes to produce these seismic disturbances..
“Earthquakes are more common than most persons think. Modern instruments for detecting slight tremors within the earth’s crust show that there is scarcely an hour in the day free from these shocks. In mountain regions, and especially in the highest and youngest mountains, erosion is most rapid, and on the sea bottom, along the margin of the continents sedimentation is greatest. In these regions, therefore subterranean temperature and pressure changes are most rapid and earthquakes most frequent.
“A study of earthquakes develop these general facts. The origin is seldom more than twelve miles below the surface; the size of the shaken region bears a certain relation to the depth of the origin or focus, the smaller shaken region indicating a relatively shallow origin ; the energy of the shock is approximately indicated by the area of the shaken region ; the origin is seldom a point, but generally a line many miles in length; the subterranean stress is not relieved by a single movement, but rather by a quick succession of movements causing a series of jars.
“The transmission of an earthquake shock through the earth takes place with wonderful rapidity. The elastic wave varies in velocity from 800 to 1,000 feet per second in sand or clay to three miles per second in solid granite.
“Sometimes these vibrations are of such a character as to be imparted to the air, and their transmission through the air outstrips the transmission through the earth and the ear detects the low rumbling sounds before the shock is felt.
“If the origin of the shock is under the sea near the coast any upheaval of the bottom of the ocean that frequently accompanies an earthquake, gives rise to a great tidal wave that frequently inundates the neighboring coast with much damage.
“While the phenomena of earthquakes and volcanoes are usually associated in the same region, one cannot fairly be said to be the cause of the other. Both are rather effects of a common cause, or rather of common causes, the chief of which is the shrinking and readjustment of the rocky strata within the earth. The suggestion that there is some physical connection between the recent eruptions of Vesuvius and the earthquake at San Francisco does not accord with the generally accepted views of geologists concerning these phenomena.
“It is probably true that a critical condition of stress between two gigantic and contending forces may be touched off, as it were, by any feeble force originating at a distance. Thus a distant volcanic eruption or earthquake shock may determine the climax of stress in a given portion of the earth, which will produce an earthquake. Observations show that more earthquakes occur near the full and the new moon than at other times. This is probably, due to the fact that at these times the gravitation of the sun and moon are combined, and their effect upon the earth is greater. We can see this effect in the higher tides at new and full moon. But these forces, it will be seen, are the occasions, and not the causes of earthquakes.
“The probable recurrence of the San Francisco earthquake is a matter of great uncertainty. In general, whenever the internal stress of the forces that give rise to earthquakes is relieved there is usually a long period of quiescence in the strata of the earth, but in the course of time, especially in regions of recent and rapid geological changes, such as is the case on the Pacific coast, there is almost certain to be recurrences of earthquake shocks from time to time.
“The geological forces may, however, gradually adjust them-selves, and it may be many centuries before-such a dynamic crisis will arise as that which has just convulsed a continent.”
California has had a number of great earthquakes. The records go back to the earthquake at Santa Ana in 1769. Not very much is known of this earthquake, though a church was built there and dedicated as Jesus de los Temblres.
Another one occurred at Santa Barbara in 1806, and still an-other in 1812. The Old Mission, about the only building there at that time, on both occasions practically had to be rebuilt.
Hittell’s History of California says that “slight shocks of earthquakes are not infrequent, but none of really violent or dangerous character has been known to occur. An old or badly constructed building has occasionally been thrown down, and a few people have been killed by falling roofs or walls. But there has been nothing in the experience of the oldest inhabitants to occasion or justify fear or dread. The first one of which there is any full record occurred on October 11, 1800, and consisted of six consecutive shocks, and it tumbled down the habitations of San Juan Bautista.
“The most disastrous shock occurred in December, 1812, when the church of San Juan Capistrano was thrown down and forty Indians killed by its fall. The same shock extended north-westward and damaged the churches of San Gabriel, San Buenaventura, Santa Barbara, Santa Inez and Purisima. In 1818 the church of Santa Clara was damaged, and in 1830 the church of San Luis Obispo.”