Popular Science Monthly/Volume 69/October 1906/The Earthquake Rift of 1906
|THE EARTHQUAKE RIFT OF 1906|
By President DAVID STARR JORDAN
LELAND STANFORD JUNIOR UNIVERSITY
THERE are two sets of disturbances which shake the crust of the earth and therefore go by the name of earthquakes. Eruptive earthquakes are explosions, usually of steam, about a volcano. Tectonic earthquakes are breaks in the overloaded or overstrained crust of the earth, and, for the most part, have nothing to do with the steam vents we call volcanoes. To the last class most earthquakes belong, certainly almost all that have been felt within the United States.
Again, under the name of earthquake we include two very different sets of phenomena, the one the rock-rift or fault, which is the disturbance itself, the other the spreading or interfering waves set in motion by the parting, shearing and grinding of the sundered walls of rocks in the earthquake fault. It is the jarring waves extending in widening and interfering circles which do the mischief to man and his affairs. It is the rift of rock which sends these waves forth on their blind mission of confusion or destruction.
In every tectonic earthquake there is somewhere a fault or rift of rock, with some sort of displacement, permanent or temporary, of the relations of the two sides. In extreme cases, this break extends for miles in a straight line, breaking the surface soil and passing downward to a depth which can be only guessed at, five or ten miles perhaps, perhaps as far down as the crust is rigid. There are undoubtedly destructive earthquakes in which the soil is not broken over the rift of rock, but as a rule, in violent disturbances, the crack comes to the surface, breaking through the overlying soil. In all severe earthquakes there are, moreover, breaks or fissures in the earth having no connection with the fault itself. These are slumps or landslides, and geologically they signify but little. They mean simply that loose soil has been shaken down. They do not go down into the underlying rock. From the true earthquake crack they may usually be known at once, because their course is determined by the topography. They are not straight. The true earthquake rift moves on in straight lines, broadly speaking, careless of topography. But topography is not careless of the earthquake rift. On either side of it, for perhaps hundreds of feet, the
the Pacific, each earthquake rift follows the line of an old fault, and the original break goes back to the mountain-making periods of Tertiary times. The California earthquake of 1906 follows the axis of an ancient break, the 'Portolá-Tomales fault' or 'San Andreas fault,' first studied, so far as I know, by Dr. John C. Branner in 1892. In this fault hundreds of thousands of earthquakes, large and small, have
preceded the recent one. In it the aggregate displacement horizontally has been very great, and the aggregate vertical displacement as shown by the rock strata on either side of it exceeds half a mile.
It is the purpose of this article to trace the earthquake rift of April 18, 1906, across the map of California. The accompanying photograph of a relief map by Dr. Noah Fields Drake will show the topography of the state. In California there are multitudes of valleys of various kinds. Those formed by water and ice surface erosion are variously curved and ramified. Such are the mountain canons of the west flanks of the Sierras. Those valleys formed or marked by earthquake cracks have almost invariably straight axes. These extend in general toward the north-northwest, more or less distinctly parallel with each other, and often intersected by cross-faults.
Examples of faulted valleys are the great valley of the Sacramento and San Joaquin, the Santa Clara Valley, San Francisco Bay, with the Valley of Santa Rosa, Eel River Valley, the Santa Catalina Channel, Owens River, the San Jacinto Valley and many others. A cross-fault extends from Monterey Bay up the valley of the Pájaro River. In some of these faults earthquakes have taken place in historic times, in others no break has been noted save that recorded in the rocks. Dr. Branner has compared a fault to a break in a bone. It represents a weak place which will give in a time of strain. On the other hand, if not freshly broken, it will tend with time to heal. A broken bone
will be naturally renewed. A faulted rock bed will be cemented in the course of ages of pressure and of cementation.
The most interesting of these breaks in California is that recorded as the Portolá-Tomales fault. Its course can be plainly traced on the relief map. It enters the shore near the mouth of Alder Creek and near the low headland called Point Arena, in Mendocino County on the north, and runs to Chittenden, on the Pájaro River, in Monterey County, on the south. The line is almost perfectly straight, and its course and direction can be determined by placing a ruler on the map, using the line of Tomales Bay as an axis. This long, narrow, straight inlet is a resultant of past earthquakes, probably beginning in Tertiary times. It is bounded on the west by mountains which have their origin in some ancient upward thrust of the walls on the west side of the ancient fault.
On the eighteenth of April the trouble began in the sea. Just where, we may find out later. We know that the center is in the sea, because where the rift enters the land it was broader and its effects more violent than at any other point along its extent. As the rift can be traced for 192 miles across the land to the southward from Point Arena, it is safe to say that it goes as far to the northward under the sea. A steamer crossing it the moment of the earthquake, off Mendocino, ninety miles to the northward of Point Arena, bears witness to this fact. The captain thought that he had struck a raft of logs, so fierce and hard were the shocks of the waves in the water. . The movements were short, quick and violent, not forming a tidal wave, but a strange choppy sea. For the time being all rollers and surf were broken up. Off the bold headland of Cape Mendocino is a deep sub-marine valley, to the west of which is a high mountain which does not rise to the surface of the ocean. In the channel between the cape and the submerged mountain the earthquake rift may be supposed to run. In this channel numerous earthquake shocks have been recorded by different passing vessels. If not itself a center of disturbance, it records the line along which great disturbances have frequently passed.
The rift struck the land at the mouth of Alder Creek, above Point Arena. It crept over the hill as a deep furrow in the black, sticky adobe, veering a little to left or right according to the resistance of the soil, but always keeping in a straight line in its general direction. It may be imagined as a sort of devouring dragon, leaving its trail on the hills and destroying the works of man wherever it passes. It is hard in following its course, not to think of it as endowed with a sort of wicked life. Its movement is properly from north to south, but the opening of the great fault seems to have been really instantaneous. It took place at 5:13 a. m. and the waves lasted forty-seven seconds. It may be noted in passing that the complication of the waves at any one point was mainly due to the great length of the rift. A point immediately near the crack felt mainly the first great shock, its wave and the return wave. A point farther away felt the wave and its return jolt, followed at once by waves from farther to the north and farther to the south, these waves becoming more and more opposed to one another. The waves would then augment, neutralize, override and otherwise modify one another, the final result being the violent twisting motion, the most remarkable trait of the latter portion of the earthquake in question.
Coming over the first ridge, from the sea, the rift passed under the long bridge over Alder Creek. The land on the west side of the bridge
was jerked sixteen feel to the north; or that on the east sixteen feet to the south—only a careful re-survey of the region can tell us which. Or it may be that both sides went to the northward, but the west side pulled away, distancing the other by sixteen feet. In any case, the bridge was torn to splinters, and the crack went on, always the west side some sixteen and a half feet to the northward, though the sticky soil tends to lag hack, and not every place shows the maximum of sheering or horizontal displacement. Passing under a barn, the rift tore it to splinters. The spreading wave displaced or destroyed most of the
houses in the villages of Manchester and Point Arena, wrecking the magnificent lighthouse of solid masonry on the Point itself. In low ground the rift formed successions of little ponds. On hillsides the lower side of the crack fell away like a drivelling lower lip, leaving an open chasm, ten to twenty feet in apparent depth. On level hard ground the soil like the rock below closed with a snap a little tighter than it was before. Line fences were broken and sheered from sixteen to twenty feet. Lines of trees met with similar readjustments. In Mendocino County the horizontal displacement is about sixteen feet. In Marin County, where exactly measured, it is sixteen feet and seven inches. Southward it becomes less. In San Mateo County it is six to eight feet, and at the Pájaro Bridge at Chittenden, where the open fault ceases, the western pier was moved northward about eighteen inches. This shifting of position, evident along the line of the crack, seems to have included the whole region, mountains and valleys, through which the crack passes. Either the region to the westward with the Santa Cruz Mountains and the mountains called Sobrante de la Punta de los Reyes have been stretched out toward the northward or else the region on the east side, including most of California, has been correspondingly humped up. It is impossible at present to say which is the fact, perhaps both. The vertical displacement is small. To the north of San Francisco the west side has been raised two or three feet. To the southward the slight relative change in elevation—two or three feet—is in favor of the east side.The rift left the pastures of Point Arena, passing up Gualala River, always in a straight line, making havoc among the redwood
trees, thence into the sea, where it runs close along the coast, past Fort Boss, throwing down everything movable in this and other towns. It then crosses Bodega Head and again falls into the sea, where it passes up the axis of Tomales Bay. At the head of the bay its course through the tules or bulrushes looks like a swath through a grain
field. Through this region (Marin County) the shock was very violent, and numerous cracks parallel with the main crack in the bay extended along the shores. In the town of Tomales, much and varied mischief was done. The parallel cracks toyed with miles of the North Shore Railroad between Tomales and Point Reyes. At Marshall the hotel was thrown bodily—and upright—into the bay, the boarders unharmed; and at aristocratic Inverness, on Tomales Bay, three summer cottages suffered the same fate. A fisherman in the bay reports that the waters receded, leaving-his boat in the mud. Afterwards they came back in a 'great wave, which looked a hundred feet high, but which was probably not more than ten.'
At Point Reyes Station at the head of Tomales Bay the 5:15 train for San Francisco was just ready. The conductor had just swung on when the train gave a great lurch to the east, followed by another to the west, which threw the whole train on its side. The astonished conductor dropped off as it went over, and at sight of the falling chimneys and breaking windows of the station, he understood that it was the Temblor. The fireman turned to jump from the engine to the west when the return shock came. He then leaped to the east and borrowing a kodak he took the picture of the train here presented.
Paper Mill Creek runs past the same village, a considerable stream, noteworthy lately from the successful stocking with king salmon. The two banks of the stream were forced toward each other so that the length of the bridge was shortened by about six feet and the bridge was correspondingly humped at its north end, an arch about six feet high being forced up.
From Point Reyes Station (at the base of the peninsula also called Point Reyes) the earthquake rift passed along the Inverness Road to Olema, where all the houses not standing on rock foundation were thrown from three to six feet to the westward, toward the crack itself.
Skinner's Ranch is a large dairy near Olema. The house stands near the road, a dairy house some thirty feet to the south of it, and a large barn with cowyard just behind that. A row of large cypress trees stood just before the house on the roadside, between them and the house a little rose garden, to the south of these, opposite and partly behind the dairy, a group or row of large eucalyptus trees.
The earthquake rift passed directly in front of the house, between the buildings and the road. All that stood to the westward of the crack was violently jerked to the north a distance of sixteen feet seven inches, or it may he that the east side moved an equal distance to the smith. If Mr. Skinner had chanced to look at the right instant he would have seen the whole row of cypress trees file past his window to take their station in front of the dairy, taking the rose garden with them. A few raspberry bushes came from farther north to take, partly, the place of the roses. The eucalyptus trees in front of the dairy moved on to a position opposite the barn, and one detached from the others and to the westward of the crack was left near the head of the line instead of at its foot. The crack passes obliquely under the barn, entering it at the northwest corner and leaving it at the middle of its posterior or southwest side. The barn remained intact, thanks to its weak foundation, Tor the east side pulled loose from the ground, and the barn went northward with the west side. Sixteen and one half feet of its former foundation at the southeastern corner is exposed. A driveway under the barn is divided in the middle. Yon pass in on the east side, the western half is sixteen and one half feet to the north
farms on the west stretched sixteen and one half feet or those on the east side crowded together to the same amount? If either, who stands the loss and what store can be set on ancient landmarks?
Next to the Skinner Ranch is the Shatter Ranch. Here the houses and barns are on the east side of the crack, but the transposition of
roads, trees and fences was the same in kind. The rift passed through the corral, and one of the astonished cows dropped into it, soon falling deeply till only rump and tail were visible. The hysterical dogs barked at her, the water came into the rift, and the dairymen, doubtless with a sense of the impotence to struggle against fate, buried her in the grave from which they could not rescue her.
Crossing the valley the rift split a small hill, throwing down four large spruce trees, all of which fell at right angles to the crack. A very large oak tree standing on level ground was shoved violently, still standing, sixteen and one half feet to the southward into the base of the riven hill, or perhaps the western half of the hill was shoved violently about the tree. Dr. G. K. Gilbert seems to think it probable that both sides partook in the motion.
On through the valley of Olema went the rift, past more dairies, but leaving their buildings altogether to the east. Crossing the road above Bolinas, the two sides of the highway are rudely separated. Reaching Bolinas Bay, the rift is visible in the mud at low tide, and good authority reports the sea-bottom to the westward, along Duxbury Beef, to be raised two or three feet. The gatherers of abalone shells venture out into regions of sea-bottom formerly inaccessible at the lowest tides. On the east side of Bolinas Bay the clams are hopelessly buried. At Bolinas the pretty Flagstaff Inn was thrown into the sea and completely wrecked. The crack again enters the sea, passing across the entrance to the Golden Gate five or six miles west of the center of San Francisco, and giving to that breezy and joyous town a jolt which will live in history, but from which the fine-spirited people will recover long before the world at large will clearly understand what their experiences have really been. The rift reached the shore again at Mussel Bock to the southwest of San Francisco. Here the cliff was hurled down, a gradual incline was made a steep one and four thousand feet of newly graded railroad was thrown into the sea. It passed up the narrow valley of San Andreas, not harming the reservoir, but wrecking all the water mains entering San Francisco from the great reservoirs, Crystal Springs, San Andreas and Pilarcitos. The dam of the Crystal Springs reservoir, across the fault line, was so well built that the visible crack passed around it along the bank by its side, returning afterwards to its former direction. The bleak and boulderstrewn saddle called Cañada del Raymundo, scarred by previous earthquakes, was then passed, and beyond it the narrow, fertile valley, Portolá, named for the first governor of California, the discoverer of San Francisco Bay. The crack runs along the base of the Sierra Morena, four to five miles west of Stanford University, to the head of Portolá reservoir; then ascends in a cañon to a saddle on the summit, connecting two parallel ranges, Monte Bello to the east and Castle Bock to the west. Down from the saddle between these runs Stevens Creek (Arroyo de San José de Cupertino) and down this creek went the earthquake crack, tearing up the road behind it. and throwing down landslides from every steep slope. Stevens Creek is made up from the union of two streams which meet from opposite directions. The crack descends the one and remounts impartially in the valley of the other. Both streams follow old earthquake tracks. Over another saddle the crack goes to Saratoga Creek. Across it and over another saddle it follows Campbell Creek, draining its reservoir. Thence it crosses obliquely the valley of Los Gatos Creek, over the hills of which Bret Harte wrote—
The ridges 'round Los Gatos Creek
Arched their spines in a feline fashion,
in the earthquake of 1818. Into this creek, from the Feely ranch. redwood trees four and five feet through, two or three hundred years old, were snapped off like whip-lashes. The rift crossed Hinckley's Gulch at right angles. This is a narrow gorge about a hundred feet deep, in which stood the large Loma Prieta sawmill. The gorge was filled by landslips thrown from both sides. The mill was completely buried, with nine mill hands, and a redwood tree over a hundred feet high was set erect and unhurt over the place where the mill stood. The bodies of six men were recovered. One of these, the foreman, was found erect, smothered in mud, hut standing with extended arms and limbs in the act of running from the mill. With him. equally erect and in the act of running, was the body of a Siberian mastiff. Their position marked the meeting point of the two walls of
the cañon. The crack went on across the hills, always in the same direction, southeast by south, till it came to the Chittenden Ranch in the Pájaro Valley. Here it tore off the hillside, destroying the highway at its base; then descended to the Pájaro River, shifting a pier of its railroad bridge about eighteen inches to the northwest. Here it met the Pájaro cross-fault. But here the straight line from Point Arena came to an end. A series of short breaks creeps off to the southeast, ending two miles southwest of San Juan, the last act being the final, almost complete, wreck of the beautiful and venerable Mission of San Juan Bautista.
That the oblique crack from Chittenden, famous as an 'earthquake ranch' of earlier times, to San Juan, is part of the original rift, is not
clear. It may be that this is part of the Pájaro cross-fault. The original Portolá-Tomales fault, if continued in a straight line from Chittenden, would pass along the flanks or the foot of the Gavilan mountains to Priest Valley, fifty miles to the south-southeast. Beyond Priest Valley is a well-marked earthquake crack, which opened in the earthquake of 1868, and in earlier times. This extends through desert land in the same direction, its course being the axis of the Cholame Valley and the uninhabited desert sink known as Carisa Plain. This old rift extends at least one hundred and forty miles beyond Chittenden to Monte Pinos in the north edge of Ventura County. This whole fault from Point Arena to Monte Pinos is clearly a single break, but only 192 miles of a possible 330 were opened in the earthquake of 1906.
But while the surface break seemed to end at Chittenden, it seems probable that the rift in the rocks below extended much farther. At Priest Valley, fifty miles along this line, the shock was violent, while at localities ten miles or more to the east and west of the line, as at Lone Oak or the Pinnacles, it was very little felt. In Priest Valley chimneys and shelving were thrown down, buildings badly shaken and the contents of a country store impartially scattered over the floor, the shock being apparently about as severe as in San Francisco.
With the opening of the great rift it is conceivable that faults in the neighborhood should also be affected. There is evidence (most of which the writer has not examined) of the opening of a parallel fault behind Cape Mendocino. This seems to have passed across the base of the cape, cutting across the smaller headland called Point Delgada, losing itself in the Sonoma Valley to the southwest of Santa Rosa. There are distinct traces of it across Burbank's famous orchard at Sebastopol. Here on a slope lines of fruit trees were shifted, a well was moved bodily three or four feet, and a crack about one fourth mile long extended across a neighboring field, its direction parallel with that of the Tomales rift. Other similar cracks open at intervals on the road toward Point Delgada. The extreme violence of the shock in Santa Rosa perhaps indicates its nearness to this second rift, as the Tomales rift caused little damage in other towns equally far away. Dr. G. K. Gilbert takes a somewhat different view of this case. He seems to regard this Point Delgada crack as part of the great Tomales-Portolá rift. In his map (Popular Science Monthly, August) Dr. Gilbert marks the great rift as swinging eastward in a curve across Point Delgada and to the eastward of Cape Mendocino between that headland and Humboldt Bay. It seems to the present writer far more probable that the Point Delgada fault is a separate rift, parallel with the main rift, and similar to it, except that it is a little less violent. There is some evidence that a fault line at the foot of San Francisco Bay opened for a short distance to the southward of Milpitas. But the soft soil in that region was filled with slumps and cracks due to the shaking down of loose deposits, and one could not be sure that the actual fault in the rocks was really disturbed. The same remark applies to the breaks at San Bruno about ten miles south of San Francisco in marsh deposits over the recognized San Bruno-Lake Merced fault. It is readily conceivable that a great disturbance like the one in the main fault might be accompanied by similar breaks in parallel or associated faults.
The chief center of disturbance in the earthquake of 1906 would seem to be in the sea. The evidence for this lies in the fact that at the point where the fault enters the land near Point Arena the displacement is greater than anywhere else. As the land fault is traceable for nearly two hundred miles to the southward, it is reasonable to suppose that the sea-bottom is broken for at least an equal distance to the northward. The point of earthquake disturbance oft Cape Mendocino has been frequently noticed in the past, and this is in a right line with the rest of the fault. It is possible that the center of trouble is located in the valley between Cape Mendocino and the off-lying submarine mountain.
There is also another possibility, very remote perhaps, but still worth considering, that is, the connection between this rift and the disturbances about the islands of St. John Bogoslof, in Bering Sea. In the year 1768, to the north of the island of Umnak and about :seventy miles northwest of Unalaska, a large island arose from the sea, In an earthquake disturbance. This island, Old Bogoslof, recorded by Captain Cook, was, as the present writer recalls it, about two miles long and fifteen hundred feet in height. In 1796, in another seismic disturbance, an addition was made to this island. In 1883 (October 28) a second island, of about the same size, arose, also from the sea, to the northward of the first. A photograph in my possession, taken in 1892 by Mr. N. B. Miller, of the steamer Albatross, shows this island, still hot and steaming. In 1896, when I visited it, it was apparently cold. These islands are supposably parts of the sea-bottom with a backing of melted rock, forced to the surface by pressure. On October 30, 1883, a severe earthquake was reported off Cape Mendocino. If on a globe one extends the axis of the Portolá-Tomales-San Andreas fault as far as Alaska, it would not fall far from these Bogoslof Islands. This fact suggested to the writer that possibly the earthquake of 1906 meant the birth of another Bogoslof. And it appears that this indeed was the case. The scanty reports which have reached us from the visit of the Albatross in May tell us that a third Bogoslof 'five times as large as either of the others' and between them, has arisen, and according to Captain Dirks, who reported the matter at Unalaska, the water was so hot that a vessel could not approach within five miles of the island. It is conceivable that' the great earthquake rift has its center in the area of weakened sea-bottom occupied by the Bogoslofs. It is possible, even probable, that the coincidence of time does not show any real connection between Bogoslof and the earthquake of 1906. Against the connection may be urged the great distance, the great depth of most of the intervening sea, and the alleged facts that the seismograph at Sitka showed a shock from the south, while that at Tokyo indicated waves from the east. It is also stated that no shock was felt at St. Paul, St. George or Unalaska, but that a great shock was felt at Unimak. Unimak, like Unalaska, lies to the east of the supposed line of the fault. In any case, the birth of the third Bogoslof is a matter worthy of thorough investigation, and its approximate coincidence in time with the earthquake in California is very suggestive.
The earthquake of 1906 is receiving the most thorough study possible, and in such a way as to give promise of important practical results. The many previous earthquakes have been recorded, but their most essential feature, the location and extent of the causing fissure has rarely been indicated. In the records we read again and again that 'fissures opened in the ground,' but whether these were rifts in the crust or mere slumps of soft ground as a rule has escaped attention. The great earthquake of 1868 opened rifts at intervals from Tomales Bay to Carisa Plain, and also a fissure on the east side of San Francisco Bay, where a straight crack about ten miles long extended from Haywards toward the south. One side of this rift showed a lateral displacement of about four feet. To this short rift, rather than to the Portolá-Tomales fissure, the shock in San Francisco in 1868 may have been due. The shock in that year was more violent in Oakland than in San Francisco and most violent about San Leandro and Haywards, to the south of Oakland. It is conceivable that the shock of 1865, having its center in the Portolá fault, not far from San Francisco, gave that city a degree of immunity in 1868. Other destructive earthquakes, as recorded by Holden ('Catalogue of Earthquakes on the Pacific Coast, 1769 to 1897') are as follows:
1812. This earthquake wrecked the mission of San Juan Capistrano in southern California, and was felt along the line of the southern missions. It had its center possibly in the Santa Catalina Channel.
1818. This earthquake injured the mission of Santa Clara; hence it may have been along the Portolá fault.
1836. This was said to be similar to the shock of 1868, its center along the Portolá line; 'great fissures were made in the earth.'
1839. This was severe from Redwood to San Francisco, 'a great fissure opened to Mission San José.' It was probably also in the Pájaro fault.
1857. Sacramento to Fort Tejón, San Bernardino and Fort Yuma. At Fort Tejón 'a fissure 20 feet wide and 40 miles long: the sides came together with such violence as to make a ridge ten feet wide and several feet high.' Fissures at San Bernardino.
1865. This was a smart shock from San Francisco to San José, apparently along the line of the Portolá fault. The severity of this earthquake, as suggested above, may have mitigated the local severity of the earthquake of 1868, which was in the same rift, but not so severe in this part of it.
1867. This was violent disturbance about Klamath Lake. A great crack said to have opened in Siskiyou County, but the locality is not recorded.
1868. A very severe earthquake, there being a rift on the east side of the bay, as also at Olema, in the Santa Cruz Mountains and for over a hundred miles from Cholame through the Carisa Plain.
1872. Owens River, Inyo County. Fissure at Big Pine 50 to 200 feet wide, 20 feet deep, extending 50 miles or more. Numerous shocks, very violent, these preceded by weaker shocks for a year or more.
1890. Mono Lake, similar disturbances.
1892. Vacaville, Winters, etc., extensive local disturbances, the fissures not traced, but said to have been along Bio de los Putos on the west side of the valley of Solano and Yolo.1897. San Jacinto Valley, with a notable fissure, the details not at hand.
To these might be added the vigorous single jolt of 1893 in the San Fernando Mountains, which did little harm because occurring in an uninhabited region. The writer was at Saugus at the time, and noted the fall of trees and the flinging of rocks down the mountainside. There seems to have been but a single wave, which would have done great injury in a populous district. It came from a short fissure in Pico Cañon.
Since the earthquake of 1906 many small earthquake waves have followed, evidently harmless details in the process of adjustment. Looking over Holden's record, we see that many small disturbances have taken place along the line of the great fault in question, besides the great earthquakes of 1868 and 1906 and the lesser ones of 1800, 1818, 1836, 1839, 1865 and 1868.
In 1808 there were twenty-one shocks at the Presidio of San Francisco. In 1812 the shocks caused a tidal wave in the bay extending up to the plaza. In 1813 or 1815 'all the buildings' in Santa Clara Valley were shaken down. There were not many and all these were of adobe or sun-dried brick. In 1851, a sharp shock in San Francisco. In 1852, a shock at San Francisco, with a fissure on the San Bruno fault, through which Lake Merced drained into the sea.
1856. Severe shocks at San Francisco, the water in the bay sank two feet.
1863, 1864. A sharp shock at San Juan Bautista.1890. Sharp shock along Portolá fault. The Pájaro bridge had a pier shifted 18 inches, as in 1906. The same crack opened at Chittenden, and the main arch in the Mission Church at San Juan Bautisia was injured. A rift opened in the soil from Chittenden to San Juan as in 1906.
It is evident that minor disturbances occur along all the fault lines in California and that but one break comparable to that of 1906 has taken place within historic times in California. This was the earthquake of 1868. This was far less violent than that of 1906, along the San Francisco peninsula, although extending farther to the south than the other. It may be remembered that the population of the region is now much greater than in 1868, and in like manner, the possibilities of mischief on the part of earthquakes has been correspondingly increased. The danger from earthquakes itself is relatively a small matter, but it should be considered in the building arrangements of regions where such disturbances are likely to recur. It is as easy to make buildings virtually earthquake-proof as water-proof, unless standing directly over the fault itself. In this connection we may close with the pertinent words of the engineer, William H. Hall, of San Francisco: "The earthquake has put a definition on the word sham, which seems positively cruel. It has established a value on the solid foundation and genuine superstructure which is indeed ennobling."
It would redound to the moral and spiritual elevation of any community to be assured of a smart shock at intervals and of a real temblor once in each generation.