Popular Science Monthly/Volume 77/August 1910/Observations on the Earthquake of May 26, 1909
|ON THE EARTHQUAKE OF MAY 26, 1909|
By Professor J. A. UDDEN
AUGUSTANA COLLEGE, ROCK ISLAND, ILL.
EARTHQUAKES are infrequent in the upper part of the Mississippi Valley, and observations on earthquake phenomena in this part of the world have a peculiar interest, not only on account of the special bearing they may have on seismological questions, but also on account of the light they throw on the psychology of an observant public which is unacquainted with seismic phenomena. The writer wishes to present some observations on the earthquake which occurred in this region on the twenty-sixth of May, 1909. They are based on notices which appeared in the public press, and which were secured from fifty daily and weekly newspapers immediately after the earthquake. The collected reports contained in all some three hundred observations on incidents which occurred during a few moments shortly before nine o'clock in the morning, when the earth waves rapidly traversed the states of Illinois, Iowa, Wisconsin, Michigan, Indiana, Missouri and Minnesota.
The reports collected indicate that the mesoseismal area of this earthquake lay in northern and north central Illinois, and reached slightly beyond the south boundary of Wisconsin. It appears also that there were no less than three epicentral tracts, one near Dubuque in Iowa; one near Waukegan, and another near Bloomington, in Illinois. At all of these places the shock was strong enough to slightly damage a few buildings. From this unusually large triangular mesoseismal area the earthquake waves spread in all directions, sensibly as far north as to Rochester in Minnesota and to Muskegon in Michigan, east as far as to Muncie in Indiana, westward toIn the central region, where the earthquakes are most complex, one report states that a distinct raise, or upward motion, was first felt, and that this was followed by a trembling. In other cases, houses and floors are said to have "heaved." In Beloit the houses are said to have been "jostled out of plumb." Violent shaking and rocking is also reported. Farther out from the central area there is a more frequent use by the reporters of such terms as "shaking," "rocking," "swaying" and "jarring," while toward the outer margin of the disturbed area houses are more often said to have been gently rocked and shaken, or to have "trembled" or "quivered," indicating the more gentle and in Iowa, and southward to Hannibal in Missouri, affecting an area of some five hundred thousand square miles.
more regularly undulating nature of the free and gradually vanishing oscillations of the earth.
The greater number of earthquakes are now known to be due to slipping of enormous blocks of the earth., along fissures or joints of great depths, and thus forming the dislocations known to geologists as faults. In the case of the earthquakes with two maxima of disturbance, the slipping occurs first at one point in such a fissure, and then at another. There can be no doubt that this Illinois earthquake was of the nature of such a compound slip, although the exact position of the fault can not be correctly located from the data at hand. In most descriptions of the shock no mention is made as to whether there was one maximum or more. Such particulars were naturally overlooked. The people of the upper Mississippi Valley are not trained in making observations on earthquakes. Nevertheless, nine observers make mention of more than one commotion. One account from each of eight localities states that two distinct shocks were felt. These places are Bushnell, Canton, Champaign, Chicago, Geneva and Sterling in Illinois, and Davenport and Dubuque in Iowa. In the latter place the first disturbance lasted about ten seconds, after which there was a short pause and then again a shock of short duration. But the reports from Chicago, Springfield and Champaign, which places lie on the other side of the mesoseismal area, all agree in stating that the first shock was of brief duration, and that the second lasted several seconds. One observer is reported as having noted three distinct shocks, and this was Professor W. H. Hobbs, at the time on a visit in Madison, Wis. He is one of America's prominent seismologists, and his testimony may be regarded as specially competent. The three shocks he noted may have been three separate impulses coming from the three epicenters previously mentioned, at Dubuque, Waukegan and Bloomington, started by slippings closely following each other in each of these places.
This inference is in a measure strengthened by some observations made on the duration of the earthquake. There are in all fifty-eight such observations, showing a range of estimates from one second to three minutes. Thirty-eight of these estimates vary from one to eight seconds and average four seconds. In six places the disturbance is reported to have lasted ten seconds; in five places, fifteen seconds, and in one, twenty. An average of these twelve estimates is about thirteen seconds. In two places the shock is reported as lasting a half minute; in three places, one minute; in one, a minute and a half, while in Dixon and Joliet the disturbance continued for three minutes. No great accuracy can be claimed for these estimates, but it will be observed that they fall into three groups, one with an average of four seconds, one with an average of about thirteen seconds and another with an average of about sixty seconds. We may suppose that the shortest average represents places where only one of the three shocks was sensible, while the two larger averages represent places where two or where all three shocks were strong enough to be felt. All places where the disturbance lasted more than a minute are somewhat centrally located, and may hence very well have been exposed to the effects of all the three shocks, each of which increased the total length of the period of the disturbance.
No less than sixty-six observations are reported on the time at which the earthquake was felt. These are of interest chiefly in showing how great is the difference in accuracy of time measurements required for general purposes, and for the purpose of seismic investigations. They also illustrate our general preference for round numbers. The reports range from eight o'clock in the morning to twenty minutes after nine. More than half of them give the numbers thirty, thirty-five, forty and forty-five minutes after eight. Discarding these figures, which are multiples of five, twenty-two observations range from thirty-seven to forty-one minutes after eight. The time recorded by the seismometer in the office of the United States Weather Bureau in Peoria, no doubt more reliable, was thirty-eight minutes after eight. The time marked by another government seismometer in Washington was forty-one and a half minutes after eight. If the velocity of the earthquake wave in traveling from Peoria to Washington, be calculated from these last two figures, we find that it approached three and three tenths miles per minute. For the purpose of determining the velocity of earthquake waves the data furnished by the press reports are of course entirely inadequate.
The location of the epicentral tracts and of the mesoseismal area is, however, clearly indicated by reports from which the intensity of the motion may be estimated, and from which isoseismal lines may be constructed.
The data contained in the press reports can be readily compared with the Rossi-Forel scale of intensities. The greatest intensity shown is in the falling of chimneys and in the cracking of walls, which barely approximates eight in the scale. It is not practical to separate these localities of greatest intensity from a more extended region where the earthquake had an intensity more nearly comparable with seven in the scale. Within this area furniture was overthrown, plaster fell from ceilings and from walls, and hanging pictures and other suspended ornaments were jerked loose from their fastenings. Outside of this most severely disturbed mesoseismal area there is a belt from ten to a hundred miles wide where the intensity approximates the next lower point in the scale. Here lighting fixtures, chandeliers and bookcases are reported to have swayed, dishes were broken, chairs rocked or were moved or overthrown, houses were rocked, chimneys cracked and clocks were stopped. Beyond this again is a zone where the evidence of the earthquake consisted in the more subdued motions described as shaking of houses and of furniture, rattling of dishes, bottles and tinware and swinging of suspended objects. This zone has a width of from fifty to a hundred and fifty miles and marks the location of the fifth isoseismal. Continuing the diminuendo, the earthquake next announced its rapid passage by the rattle of windows, the jarring and quivering of houses, and by gentle shaking and trembling of furniture. This is the fourth intensity, and characterizes a zone that merges imperceptibly into the next, where few people noticed the disturbance, and where it appeared as a merely perceptible jar, or a slight undulation, most frequently noted only in the upper stories of high buildings. In this gentle form it disappeared to human senses at a distance, in all directions, of some four hundred miles from the central region. How much farther did it speed, unseen, unheard and unfelt? You will remember that it left a record on the seismometer in Washington. This city is nearly four hundred miles beyond the zone where the waves ceased to be perceptible to the unaided human senses. From this record we may infer that in the brief span of two or three minutes the earthquake waves spread over a circular area about sixteen hundred miles in diameter.
A classified review of the little things that happened in the upper Mississippi Valley, when a block of the earth slipped in the northern part of Illinois may perhaps be of interest. The phenomena reported, affected at least five of the human senses, the senses of general well-being, of touch, of equilibrium, of hearing and of sight.
A rheumatic woman in the zone where the disturbance was very feeble "felt the vibrations keenly and told others of the earthquake, before it was generally known." Another woman, in poor health, ascribed the peculiar feeling that she experienced to an attack of heart disease, and sank frightened in bed. Experiences of this kind have been noted in other earthquakes and appear to be due to a morbidly excitable condition of the ill-defined and unspecialized sense of general well being. Some people perceived the earthquake chiefly through the sense of touch, as when a man, seated in a chair and resting his legs on a railing, "felt his legs shake," or as when a chief of police, also seated, felt that his chair shook. In several other cases the earthquake was likewise merely "felt." No doubt the sense of touch entered as an important element in a far greater number of instances when mention is made that something shook, trembled, quivered or rocked, or when there was a jar or a tremor. The sense of equilibrium or of poise was evidently involved in the case of a man who felt "dizzy," and in the case of people who "wabbled on the streets," in cases where occupants of houses noted a "heaving," "rocking" or a "swaying" motion, and when people "were thrown down," or "nearly tumbled over," or "found difficulty in keeping on their feet."
The reports mention only five instances of sounds accompanying the earthquake. Such sounds are general in the mesoseismal area in all severe earthquakes in all parts of the world, except in Japan, and one noted seismologist believes that their absence in that country is due to a racial inability among the Japanese to hear sounds of very low pitch. The general absence of sounds in the Illinois earthquake is readily accounted for by its comparative weakness. It was faintly audible only in three epicentral tracts. Some parties claim to have heard a distinct rumbling before the shock in Dubuque. In Waukegan one man described the quake as a rush of wind, and said that he had heard it. This swishing noise is one of the many known characteristic forms of earthquake sounds. In Springfield, 111., a faint rumbling was heard, and a janitor in one of the school buildings in Peoria made a similar observation. One man heard a sound like the "bumping of a locked door." This is another variation of earthquake noises, which, when more powerful, resemble volleys of musketry and artillery, and which, like the other noises, originate under the ground. Many observations involve sounds which are, as it were, proxies of the quake, induced by secondary events, such as the rattling of windows and dishes, the crash of falling brick and the like. The student of earthquakes depends, as we have seen, on such noises for much of his information on the progress of the earth waves in the peripheral region of the disturbed area.
The sense that gives us the most reliable information on earthquakes, as on most other physical phenomena, is the sense of sight. Visible earth waves are, however, rarely seen except in severe disturbances. It is uncertain whether they appeared anywhere in this case. but there is a suggestion that they were rioted in Waukegan, where the sidewalks were seen to "heave." A high bridge near Dubuque, Ia., and some old buildings in Plattsville, in Wisconsin, were seen to "sway." But motions of such structures, as well as motions of smaller objects, indoors and outdoors, are merely the effects of the earth's motion and not a part of the earthquake itself. It is unnecessary to enumerate them here.
Another classification of the earthquake phenomena takes into consideration the different objects giving evidence of the seismic motion and the terms used by the observers in stating how these objects were affected. It presents simultaneously in this case, a study in journalistic diction and in mechanics. Forty reports relate the varied behavior of buildings and houses. These are said to have shaken (17), rocked (7), trembled (4), swayed (3), cracked (3), to have been jarred (2), to have quivered (2) and to have creaked and heaved, respectively in as many cases as indicated by the inserted figures. Observations on dishes, bottles and tinware are next in number. These mostly rattled (15), or were broken (8). Some were dashed to the floor (6), others merely fell (3), some were shaken (3), were moved (2), or they rocked, trembled, wabbled and were disturbed. A crockery store in Dubuque sustained a damage of some eight hundred dollars. The words used in describing the motions of furniture present a turbulence of performances of almost kaleidoscopic variety. Chairs, tables, beds, bookcases, even sedate stoves shook (8), were moved (6), were overturned (3), swayed (2), quivered (2), trembled (2), broke, were upset, tipped over, threatened to tumble over, rattled, rolled back and forth, rocked, heaved and "had the glass shattered." Windows and doors rattled (12), and shook (3), and one door was "sprung so it would not close." Hanging pictures and mirrors engaged in a variety of diversions. Some swung (3), some were shaken from the walls (3) and some were thrown from their fastenings. One mirror "trembled on the wall," and another "fell from the wall." One is said to have "jumped around" and one was "demolished." Light fixtures and lamps swayed (4), heaved, shook, were shaken from their rests, were overturned, fell and broke, or were knocked down, and one gas flame was "shaken out." Chimneys fell (4), toppled over (2), were razed, shaken down and cracked. Water and milk in tumblers and pans were spilled (5) and tippled. At Sabula a wave was thrown up against the bank of the Mississippi River. Bric-a-brac was shaken off, tipped off and thrown down from mantles (6) or simply fell to the floor. Four clocks were stopped. Heavy machinery rattled or "shook in good shape." An elevator swayed and some linotype machines swayed violently. Telephone wires were seen to sway, a telephone receiver was knocked off its hook, and a telephone instrument was "put out of commission." Other public utilities suffered serious damage, several thousand dollars being needed for the repair of disjointed gas pipes in Chicago and its suburbs. Goods were thrown from the shelves in some stores. In the watch works in Elgin some delicate instruments were thrown out of gear, and in a printer's office in Dubuque some type, locked in a form, was pied. A kitten was thrown across a room.
There was one class of accidents, some serious and others comical, which could not have been foreseen as the results of an earthquake. These involve some trigger-like arrangements. Falling stoves and disjointed stove flues caused several fires in Aurora and Chicago. In Waukegan the shock disarranged the bins in a feed store, and some of the grain was let out through a crack between the boards. The leg of a piano was loosened and fell in a school in Oak Park. The whole instrument was in this way upset and tumbled down on the floor, and the accompanying crash and noise naturally frightened the children.
Many reports describe the mental state and the behavior of people on experiencing the unusual sensation of the earthquake. In the epicentral tracts some were terrified, many left, or fled or rushed from their homes, or from buildings where they were working. There were several small panics among laborers and among employees in factories. People were alarmed and excited and ran on the streets. Some schools were dismissed for the day and instruction was interrupted in two university classes. From farther out in the disturbed region some papers state that the people in the upper stories of some high buildings were frightened, and from still further out reports mention that people were surprised or merely that they perceived the physical sensation, evidently unattended by any emotion.
The tendency of the human mind to make inferences and draw conclusions is pointedly illustrated by many of the reports. In cases where the earthquake was not recognized, the disturbance noted was nevertheless invariably ascribed to some cause, more or less remote, but suggested through the bias of previous experience. Many people thought the jar they felt was due to an explosion or a blast in some quarry, and others thought it was due to the moving of some heavy object in the building they occupied. A janitor in a school building thought that a man engaged to repair the flag pole had fallen on the roof. A grocer who had piled up some sacks of flour in the second story, went up to see if these had fallen down. People living near car lines and railroads referred the commotion to passing cars or trains. Residents in the cities were reminded of the passing of heavy vehicles. Two unsophisticated children jumped out of a bed that shook, ran crying to their mother and reported that the bed was falling to pieces. A young lady stenographer in Chicago, more versed in the ways of the world, felt her chair rocking and promptly rebuked a supposed offender at her back with the command: "You stop that."
Projected forward instead of backward, reasoning results in the vision of things impending. Here also the bias of earlier experience and of training plays an important rôle. Remembering the recent disasters in Europe, Italian laborers in Chicago quit work to fall on their knees and pray. Recalling a prophecy of the coming of the end of the world three days later, some Zionists are reported to have concluded that the earthquake was the beginning of the fulfillment of the prophecy. Some persons who had left their houses, refused for hours to enter them again, fearing a repetition of the earthquake. A prisoner in a jail is said to have speculated on his chances of getting away, in case the walls of the jail would fall, and some people in Chicago feared the coming of a "tidal" wave from Lake Michigan.
It is well known that afferent impulses, especially if they are powerful, have the effect of inhibiting or interfering with central psychic activities. Such inhibition was probably responsible for the forgetfulness of a reporter who sent in his account of the earthquake in a neighboring city to a newspaper in Clinton, but forgot to affix his signature. It explains also the action of a woman in a hospital, who was walking on crutches and who ran out without them, to escape from the building. With the inhibition of man's reason, his instincts take its place, and it would seem that many of our instinctive actions are not much different from those of the brute. They are exemplified in the panics that took place in a few factories and schools. When people rushed from buildings and started to run on the streets, they acted on instinctive impulses. These actions must have been prompted by a nervous mechanism quite like the mechanism that started several runaway horses in places where the earthquake was sufficiently severe to appear alarming. The launching of sensational rumors during a general excitement is traceable to a related instinct, only more refined and exclusively human. The reflex was started on this occasion by a fire in a kitchen in Aurora, and the reaction announced that "Aurora is burning up."
One phenomenon in this connection is almost embarrassing to mention, in view of the present growing sentiment in favor of women's rights and woman suffrage. It appears from the effects of the recent earthquake on the American people, that human reason is more readily inhibited in the gentler sex and in children, than in men. The statement may be worded in another, and perhaps a better way, by saying that human instincts are relatively stronger in woman than in man. This statement will hardly pass as anything new. This distinction is implied in the wording of one report, which states that "men were excited, women and children frightened." It is stated that in Dubuque a panic was narrowly averted in a shop where women worked. In an office building in the same city it happened that the women rushed in a panic to the stairs, and that men met them and quieted them. In a home for young women the jar is said to have "scared the occupants out." Several panics occurred in schools. One man relates that his wife and sister "rushed to him." Nurses were alarmed in a hospital. Telephone girls left the switch-boards in Chicago, and "were scared" in Clinton. A particular mention is made of a seamstress who was alarmed, and of another woman who sank frightened on a bed. But in no case is a man specially mentioned as having been afraid. In places where men were scared, fright was general, and there was then no cause for such special mention. The evidence of this difference can hardly be charged to an unconscious discrimination by the reporters in favor of the stronger sex. It must be regarded as a noteworthy incident in this earthquake that its intensity was near that limit, which is strong enough to scare women but not men. This limit must approximate seven in the Rossi-Forel scale, and the unsentimental seismologist may hence add another criterion for correctly locating the seventh isoseismal.
One general observation which has a practical bearing should perhaps not be left unmentioned. It is that the earthquake was more strongly felt in the upper stories of high buildings than on the ground floors. In Dubuque "the upper part of the high buildings swayed." A reporter in Burlington says that the shock was "felt most in the upper stories of tall buildings." "The floors shook in the upper stories of large buildings "in Clinton, and in Davenport" the tremors were mostly noted in high office buildings." In Chicago the shock was not felt on the ground floors, but mostly "only in the higher stories." The top floors are especially mentioned as having shaken in some of the university buildings in Evanstown and in a college building at Cedar Rapids. In the architecture produced by the demands of industry and business in this part of the world, the eventuality of a severe earthquake has not entered as an element of consideration. The experience of a half century shows that this neglect is probably justified. Nevertheless, it is appalling to contemplate how different the story of this recent jar would appear if the intensity of the disturbance had been just a little greater than it was. From our past experience we may safely infer that the valley of the upper Mississippi is in a region where earthquakes are not frequent. Are we also justified in believing that when such disturbances do occur, they will not be severe? The violence of the New Madrid earthquakes a hundred years ago makes the answer to this question uncertain. Time alone will tell.