AMERICA'S EARTHQUAKE SURVEY

New Zealand Graphic, Volume XXXVI, Issue 18, 5 May 1906, Page 23

AMERICA'S EARTHQUAKE SURVEY

HOW THE MYSTERIOUS CONVULSIONS OF THE EARTH’S CRUST ARE DETECTED AND MEASURED. A HITHERTO BUT LITTLE EXPLORED FIELD OF APPLIED SCIENCE.

(By

John Elfreth Watkins.)

FOREWORD. (In view of the recent terrible disaster in California, the article printed below will be read with special interest. It is from the ‘'Technical World Magazine.” — Ed. ••Graphic/*!

An eathquake survey of the United States and its possession is one of the most recent enterprises of science. Seismologists—the students of these phenomena—are learning that Mother Earth is a much more tremulous creature than we have previously had reason to suppose. In fact it would almost appear that she is growing palsied as the chill of old age creeps over her. If it is not straining imagination too much, it may be said that these seismologists are setting earthquake traps in various nooks and corners of our vast domain. These are among the most sensitive products of the instrument maker’s fine art. They have a Hindi more acute sense of touch than has been given to man. In fact, they would almost seem to have been endowed win brains, for they automatically write with pen and ink all that they observe, and their records are kept with a superhuman exactitude. ‘ SEISMOGRAPHS INSTALLED. The Government recently purchased in Germany six sets of the most improved apparatus of this category. The-e. known as “seismographs” or "seismoscopes,” have been installed at Washington, D.C.: Cheltenham. Md.; Baldwin. Kan.; Vieques Island, Porto Rico; Honolulu, Hawaii; and Sitka. Alaska. The Washington instruments are installed in a subterranean vault beneath the Weather Bureau, where they are in charge of C. F. Marvin. Professor of Meteorology in that institution. The other five sets have just been put in place in the new federal magnetic observatories at the other points named. They are being operated under the general direction of Dr. L. A. Bauer Chief of the Division of Terrestrial Magnetism, United States Coast and Geodetic {Survey. Added to this chain of stations are others at Manila, Philadelphia, and Baltimore. The first-named is in charge of •Father Algue, a Jesuit scientist of the Manila Observatory. The Quaker City's station is at Swarthmore College: .and that of Baltimore, at John Hopkins University, where it is under the direction of Prof. IL F. Reid, the most eminent of American seismologists. Professor Reid's station is serving as the clearing house, so to speak, for all of the American earthquake data: and. as soon as the co-operating stations shall have completed a sufficient continuous period of observation, he will issue statistics which no doubt will surprise us all. Foreign stations, also, are~-co-operat-ing in this work, particularly those at Toronto. Ont., and Victoria. 8.C., under the meteorological establishment of Canada: and others at Mexico City: Corboda. Argentina; and Arequipa, Peru, in fait, arrangements arc being effected, looking to the perfection of an earthquake survey of the world under the auspices of the International Seismological Association. This society has been organised for this special purpose under the leadership of Professor Gerland. Director of the Seismological Observatory at Strassburg, Germany. Japan will fall into line with nearly 1000 stations; Italy, with 15; England, with 3; Scotland, 2: India. 4; Canada, 2; Australia, 3; Russia, 3; and Spain, 2: also South •Africa. Egypt, Ceylon, Java. Mauritius, New Zealand, Syria, Trinidad, Mexico,

Peru, Argentina, and Germany, each 1. Thus Old Earth will have left but few surface areas where she may twitch undetected. But, as to our own earthquake survey : The six seismoscopes which we have installed are regarded .c the most perfect of their class. The pattern is a modification of the recent invention of Professor Omori, secretary of the earthquake investigation committee of Japan, Japan is the groat earthquake country, and has gone so far as to institute a chair in -eismology at the University ot Tokio. HOW THE RECORDS ARE MADE. This new type of seismograph consists of a heavy weight, so suspended in front of a tail iron pedestal as tn be always in neutral equilibrium and unaffected by any influence Other than gravity. While the earth is quaking and trembling directly below it. it is standing still for the moment. It is spanned by an iron arch, who-e base is a stone pier, penetrating the earth. All earth movements are directly communicated to the areh. Hence, when even the slightest tremor takes place, the arch moves therewith, but the weight below remains quiescent, as already said. — Attached to the stationary weight by a jewelled pivot is a long, slender, arm of aluminum, with a writing r>en at its outer end. Upon the same foundation with the arch, and sharing all earth movements therewith, is a revolving wheel, whose broad tyre is a sheet of paper, against which the writing pen rests. The principle of the instrument, in a nutshell, is that each earthquake moves the paper against the pen. and records its tremors in zig zags or curves. But. by a delicate adjustment, the aluminum arm exaggerates the earthquake tremor to a measurable degree. The wheel, with its paper tyre, makes one revolution every hour. The recording pen commences its record on one edge, and. few aid of a thread on the wheel's axle, is made io trace gradually a perfect spiral over the endless band of paper, unless an earthquake interrupt-. Thus the normal lines of the pen do not overlap. By means of an electromagnet attached to a specially made clock, a current is communicated every minute to another pen point, following the first and resting upon the same paper. The latter gives a hitch each time it receives an electric impulse, and thus checks off minutes along the spiral line traced by the first pen. which is “keeping tab” on Mother Earth's antics. A new paper is placed on the wheel at the same, minute each day. It being known precisely when a new record is set, the exact time of a zig-zag earthquake line can be determined by counting the minute marks on the paper: and the exact second of an earth tremor's beginning can be leafrn<-d by applying a delicate scale dividing by sixty the space between two minute marks. A pair of these instruments is necessary at each station. One. always pointed north and south, records earthquake vibrations moving east and west: the other, directed east and west, detects north and south movements. Each tremor makes its record on both instruments simultaneously. The zig-zag lines will l>e seen to differ materially when the paper strips are taken from the wheels and carefully compared with a scale. The exact direction of the earthquake wave, as well as its horizontal width, is thus measured to a nicety, DELICACY OF THE WORK. Only one out of several hundred or perhaps several thousand earthquakes

recorded by these instrument*,, is perceptible to the public or reported by the newspapers. Typical of these earthquakes notii-vd month after month, was vu? caught by the Weather Bureau’s seismograph just after its installation. On looking over the record sheets at the time of the daily change. Professor Martin di»c .vered a zig-zag perfectly inscribed anil showing all the recognised characteristics of earthquake phenomena. The curve showed that there were preliminary tremor* commencing at 9.39 a.m. -and lasting five minutes. The main tremors then succeeded for 2 minutes 36 set* •nd.*. Terminal tremoifc lasted for 26 winu 21 second*. The total disturbance lasted 34 minutes. At the height of its activity, the earth beneath the instrument moved only a trifle more han a hundredth of an inch, from side to side. Small wonder, then, that the public unav.are of the shook. But tiiis tiny earthquake, undiscovered by pre** or public, travelled across the continent and wa? felt on the Pacific s'oj.T by a similar seismograph. Without announcing the fact that his instruments ha 1 r<ni.rdol the shock. Professor Marvin fi’ J their re-ords away and corresponded with other »t i lions. He found that those oi Baltimore. Victoria, and T« nurto bad recorded the shock at abcut the *ame time. By careful compulation, ho discovered that its first strong wave* travelled fr<-m Victoria across the v niinent to Toronto in a fraction over eighteen minutes, and from Toronto to Washington in one. and one-half minutes. The stronger waves travelled at the rate of nearly two miles per second. That earthquakes will some day be systematical’y forecast, is a prophecy which may sound visionary, but one which has some scientific foundation. The Japanese Musmclogists now believe that they find indications of earthquakes’ approaches upon the records of their magnetic instruments, preceding directly the effects shown by their seismographs. In other words, they have found what appear to lie magnetic warnings of earthquakes. If their theory can be demonstrated, our Weather Bureau will d. übtless profit by it; and we may expect, perchance, to see earthquake warnings displayed from mastheads alsvr our public buildings, or to read at the lop of the morning paper that Mother Hearth will indulge in a shake-up at such or such an hour of the day. Pastors may then have time to gather in their flocks for public prayer, or urban residents nVy betake themselves to the open country, before the crash comes. FREQUENCY OF EARTHQUAKES. In Ifo4. at Baltimore, fifteen earthquakes were recorded by Professor Reid between April 1 and October 21. In Porto Rico, seventeen were observed by the national instruments between April 1 and July 1: in Honolulu, thirteen were counted within this latter period. According to th****' figures—upon the basis of which it is hardly fair to generalize, however—an earthquake shakes our Eastern States on an average once every two weeks, while the frequency is considerably greater both in Hawaii and in Porto Rico. The national instruments have not been installed a sufficient time fur any statistics to have been gathered elsewhere.

Garthquake, and magnetic .terms are found to lie related, and it is partly for this reason that the Government', new. magnetic observations are being equipped with seismographs. The primary object of the national earthquake survey will be the determination ot the velocity with which shocks and vibrations are propagated over the Surface of the earth and through its interior; to locate positions of earthquake origins under the oceans; and, generally, to increase our knowledge ot the ]>hysical nature of Die earth's crust and its interior. The average velocity of earthquakes, as thus far estimated, is about 1| utiles per second for the first tremors, and about one mile per secund for the main shock. After a few hundred miles, the velocity of the first tremors increases, and over long distances has been estimated to be greater than that of the waves of compression through steel or glass. The fact that the vibrations of the first tremors appear to travel faster than those of the main shock, indicates that the former pass directly through the earth, while the hitter follow the longer course around its crust. Mother lyrtli appears to quake, at some point or other, on an average, once every half hour. In Japan, more than a thousand earthquakes per year are regularly recorded. Great Britain's dominions are crossed by tremors about 10i> times a year. For our own country, we have no complete figures as yet. In both hemispheres, according to such statistics as are now available, earthquakes are more frequent in winter than in summer. This is believed to be due to the fact that in the cold season the greater weight of snow and the greater pressure of the atmosphere imposes a heavier strain upon the earth’s crust. HOW EARTHQUAKES OPERATE. In many instances, shocks so faint that they eaunot be perceived by our senses when we are upon or near the ground, are distinctly felt upon the top floors of tall buildings. Severe shocks are accompanied usually with sounds comparable to those of near or distant explosions. Other effects of great earthquakes are fissures and faults in the earth’s surface the raising or lowering of areas of ground: the drying of springs; landslides, land waves, and tidal waves. The fissures in the earth's surface may open widely, and immediately close, or they may remain open with a width of several feet. Some have had such immeasurable depth that water from streams has flowed into them for days without filling them, while others have belched up gases, water, or mud. appearing as if from the crater of some slight volcano. Sometimes large areas of land are depressed, forming the basins of new lakes; and in frequent instances a large area of land has fallen to a lower level, leaving a definite wall or terrace between it and the soil not so affected. These severe shocks sometimes precipitate boulders down mountain slopes, or cause landslides or avalanches that bury settlements of people or throw dams across streams, creating lakes where none before existed. Subterranean earthquakes are observed to give rise to surface waves similar in formation to those caused by drop-

ping a pebble into a brook, but much more enormous in height, and often attaining the fatal form of a tidal wave washing inland and drowning hundreds of people. Luminous appearancesTtave been repotted as accompanying earthquakes occurring at night; and it is thought by some that these phenomena are due to the friction of moving masses of rock. According to this theory, temporary electric currents are, as a result of such friction, established in the line of the earthquake. At or near the starting point of great earthquakes, there is sometimes evidence of the bodily displacement of many cubic miles of material. When this matter is of volcanic origin, it is, according to.one authority, almost invariably magnetic, and its readjustment produces magnetic storms. HISTORIC AMERICAN EARTHQUAKES. Our most notable earthquakes have been those occurring in New England, iu 1638; New England and New York, 1663; New England, 1727; New England and the North Atlantic States, 1755; iha Mississippi delta. 181112; Inyo Valley. California, 1872: and Charleston, S.C. 1886. The earliest of these—on June 1* 1638 —occurred between 3 aud 4 pan. The .weather was clear and warm, and the ■wind westerly. All of New England, it is recorded, was violently shaken by a convulsion accompanied with a noise as of continued thunder. The main shock lasted about four minutes, (luring which the earth shook with such violence, that 5n some places people could stand only with difficulty, while many movable articles iu houses were thrown down. The earth is reported to have been unquiet for 20 days following this shock. The earthquake of 1663 occurred on January 26. aud was felt in Canada, throughout New England, and in New York. In Canada, says a contemporaneous writer, “Doors opened and shut of themselves with a fearful clattering. Bells rang without being touched. Walls were split asunder. Floor separated and fell down. The fields put on the appearance of precipices, and the mounttains seemed to be moving out of their places. It is recorded that during this convulsion of nature, small rivers were dried up; some mountains appeared to be much broken and moved; while half way between Quebec and Tadousae, at the mouth of the Saguenay, two mountains .were shaken down, forming a point of land which extended some distance into the St. Lawrence River.

The upheaval of 1727 was felt at 10.40 a.m., October 2'.f. The inajn shock lasted about two minutes; and its course seemed to be from the Delaware River to the Kennebec, a distance of about 700 miles. Pewter and china were east from their shelves. Stone walls and chimney tops were shaken down. In some places doors were burst open and people could hardly keep their feet. On the same day, the West Indian island of Martinique—where in 1902 occurred the terrible eruption of Mont Pelee —was threatened with total destruction by an earthquake lasting eleven hours. And in this connection it is an interesting fact, that during the recent disastrous outburst of Mont Pelee, no earthquake shocks were recorded by the crude seismograph then mounted in the Weather Bureau at (Washington, although severe magnetic storms were observed with the instruments of the Coast and Geodetic Survey. The earthquake of 1755 was felt from Chesapeake Bay to the eoast of Nova Scotia —or for about 800 miles. The shock occurred on November 18, and in the interior of the country it seemed to liavo extended over n thousand miles from northwest to southeast. In Boston, Mass., a hundred chimneys were toppled over and levelled with the roofs of the houses, while 1500 others were more or less shattered. The ends of several brick buildings were thrown down, ami the

vane on the public market was hurled to the earth. At New Haven, Conn., it was reported, “the ground moved like waves of the sea; the houses shook and cracked; and. many chimneys were thrown down.” This shock occurred at 4.0 a.m., and lasted four and a-half minutes. At the same time there was a great tidal wave in the West Indies.

Hie Mississippi delta earthquake of 1811-17, known also as the "New Madrid earthquake,” was characterized by severe shocks .occurring at short intervals during a period of several months. Indeed the entire series of shocks covered a period of about two years. There were few settlers in the country at that early day, and little is known as to the distance at which the shocks were perceptible. The land was plainly Been to lock with a wave-likc motion, which was communicated to the forest trees, some of which were uprooted while others were permanently entangled with one another. From the fissures opened into the earth, mud spurted up into the branches of trees, and the deep openings into the ground yawned and closed with each successive shock. Lakes which had sparkled in the sunlight of centuries went out of existence, their waters being drained into these fissures. New Lakes were created by the falling of the land, which was thus shaped into basins receiving the flow of brooks and creeks. One great area 60 to 80 miles long and half as broad, sank from its former altitude.

The Inyo Valley earthquake of 1872 continued for two or three months. The chief shock lasted but a few minutes, and those which followed at intervals were far inferior in violence. Along the base of the mountain range, was created a fissure forty miles long, and the land to the east of it fell several feet. In one place the earth dropped twenty-five feet. The ground also twisted in a horizontal direction. The fence on one piece of property was found to be fourteen feet out of alignment. A river was temporarily swallowed, and a number of springs permanently dried up. Every house in Inyo village tumbled down, and one-tenth of the inhabitants lost jjheir lives.

Twenty-seven people were Killed outright by the great earthquake at Charleston, South*Carolina, August 31, 1886. Other victims died afterward from injuries received during the catastrophe. A large number of houses were thrown down, and nearly all buildings in the city were more or less injured. The damage to property was computed in millions of dollars. The principal shock occupied about one minute, others following with diminishing violence. Destructive tremors occurred for four weeks, and others were felt for several months longer. Numerous fissures yawned in the surrounding country, sending forth water and mud and flooding the channels of streams. Railway tracks were dislocated and buckled. Had adequate seismographs been in place during any of these great earthquakes, science would have added greatly to its meagre fund of knowledge concerning the cause of such convulsions. The next great shock will be followed about the earth, and. it is devoutly hoped, will be traced to its subterranean source.