Earthquake Researches in Japan
Tokyo, November 23rd, 1886
Japan, essentially the land of volcanoes and earthquakes, has happily been thus far free from fierce terrestrial disturbances of the class manifested during the last few years in so many other parts of the world.
We have, it is true, kept up our usual earthquake average, which is certainly not less than two palpable shocks per diem for the whole country.
But since 1855, when the terrible Tokyo earthquake destroyed some 16,000 buildings and brought death to tens of thousands of people, there has been only one shock of great intensity, while of the half-dozen volcanic outbreaks that have occurred during the same period, not one has approached the dimensions of a castrophe.
For all this, Japan, as the world knows, is and has been for many years the chief seat of learning of the science called seismology.
Circumstances here are peculiarly favourable to the pursuit of that cult.
The constant repetition of the phenomena provides opportunities for sustained observation and research to which no other country affords a parallel.
There is also an extensive Japanese literature on the subject, consisting of calendars and monographs which relate to particular earthquakes and volcanoes, as well as numerous general treatises on seismic matters.
And, above all, there has been in Japan for the last 11 years a gifted English geologist and mining engineer, able and eager to make the most of these fine opportunities - a hard-working and hard-headed man of science, who, bringing to his self-imposed task great erudition and qualifications, an acute mind and indomitable perseverance, has succeeded in raising the practical study of seismology in this country to the high level it at present occupies.
The fertility and industry constantly shown by Professor Milne in observation and experiment, in collating and assimilating facts and records from all quarters, in striking out new lines of research, and in organizing systematic work, are astonishing even to those who know him best.
From time to time his results are made known, in a more or less concrete form, by publications in the Press, papers-read before the Seismological Society of Japan, of which he is the mainstay as well as founder, lectures in Tokyo and Yokohama, and commnications to learned societies at home.
These, together with occasioinal essays by such able contributors as Professors Shida and C. G. Knott, of the University of Japan, and others, present at any time a fairly complete picture of the state of progress of seismological investigation at its head-quarters in this country.
Of productions of the above classes which have appeared during the present year the most interesting are-Professor Milne's paper on Seismic Surveys, read before the Seismological Society of Japan in January last, and afterwards elaborated into a paper on Construction in Earthquake Countries, for the Institution of Civil Engineers; his lecture on the Causes of Earthquakes, delivered to the Science Society of Tokyo a few weeks ago; and essays on Earthquake Frequency and Earth Currents by Dr. Knott and Professor Shida.
About three years ago it was suggested in more than one article in The Times that practical seismologists might do worse than turn their attention to discovering means of selecting the safest building sites in earthquake countries, and to ascertaining the methods of construction best calculated to ward off the effects of shocks on buildings.
At that very time Professor Milne was occupied in investigating both of these matters at the Engineering College in Tokio, where I have often had the privilege of witnessing his methods and results.
For the first of them, he had recourse to a seismic survey of a selected area.
This was effected by an ingenious arrangement of several delicately acting, automatic bracket-seismographs, of identical construction and behaviour, which were established at various points of the area to be surveyed, and so connected with a central electrical mechanism that each one should furnish a record of any earthquake, strictly comparable with all of the other records.
At the site chosen for these experiments it was found, broadly speaking, that high ground enjoyed a much greater freedom from earthquake effects than low, marshy ground in the close vicinity.
And the results generally established that, wherever opportunities for similar experiments might exist, it would be practicable to determine definitely the safest sites for building purposes.
Concurrently with this work, earthquake-records written by a seismograph placed on hard ground at the bottom of a pit ten feet deep were compared with records of the same shocks written by an instrument on the surface close at hand.
The results were of surprising interest, showing the vibrations in strong shocks to be so superficial that they were practically cut off from the instrument in the pit, where the motion of the ground was only a small fraction of that on the surface, and was, indeed, altogether inconsiderable; though, strange to say, in small shocks the difference was much less apparent, the tremors at the pit-bottom being, in fact, nearly a constant quantity for all of the shocks observed, whether small or great.
As a whole, these experiments demonstrated that, after similar invesigations at any proposed site, it ought to be possible to arrive at safe conclusions whether buildings having isolated foundation walls or piers, carried up from ascertained depths, as in the case of astronomical instrument piers, may not be rendered safe from earthquake shocks of ordinary intensity, or at least from such of them as have their origin at distances sufficient to render the vibrations practically horizontal.
It is interesting to note in connexion with this subject that, as Professor Milne points out in his recent work on Earthquakes, in the International Scientific Series, the old Romans and Greeks found that caverns, wells, and quarries protected buildings from disturbances of the earth; that in Rome wells were dug round the Capitol for this purpose; that, according to Humboldt, the same was done at San Domingo; and that Quito is said to receive protection from numerous canons in its neighbourhood.
In a third series of experiments, Professor Milne sought the best means of employing the inertia of a building to neutralize earthquake effects.
With this object he set to work on a principle first applied by the late Mr. D. Stevenson, C.F., in connexion with the lighthouses of Japan.
Mr.Milne's method was to raise a one-storied wooden house on pier-supported beams, introducing at the points of support round shot carried between iron plates shaped and affixed for the purpose.
After many trials, beginning with ten-inch cannon balls, which, as well as several of smaller sizes, were found to be too free in their action, the best result was obtained with a handful of cast-iron shot of a quarter of an inch of diameter, working between flat iron plates at each pier-head.
These, while affording due stability to the house during high winds or internal movements, enormously reduced the motion caused by shocks; and the method proved itself to be undoubtedly well suited to bungalows or other light structures in countries liable to earthquakes.
Such, put briefly, are the results thus far reached by Profesor Milne in his efforts to solve the problems named at the beginning of this paragraph.
It, of course, will not be supposed that he has yet overcome the whole, or even a considerable part of the difficulty.
But he has at least discovered means by which some of the danger and anxieties incidence to residence in earthquake-ridden countries may be sensibly reduced.
He is also hard at work on further investigations of this class; and it may be safely said that the task could be in no better hands.
Of the important subject of the causes of earthquakes, Professor Milne's recent survey is highly interesting and in many respects fresh.
Among the theories, dating wholly from past times, which may be called unscientific, the chief is the old idea, held in Europe in the middle ages, and still prevalent among the negroes of the Eastern American States, the Mussulmans of Java, and other superstitious folks, that seismic disasters are wrathfully inflicted by Heaven upon sinful man, as punishments for past transgressions and warnings to repent..
In the unscientific class are also to be included the ancient myths-or rather one myth appearing in different forms in many parts of the world-according to which earthquakes have been very generally attributed to some creature living underground.
Thus, in Mongolia earthquakes are said to proceed from the heavings of a subterranean frog.
In India there is the world-bearing elephant; in Celebes, the world-supporting hog; and in North America the earthquake producing tortoise.
Mussulmans have a world-bearing bull.
In Siberia earthquakes are set down to the trampling of mammoths that live underground, and in Kamtschatka to the scratchings of certain flea-ridden dogs, which attend the god Tuil on his walks.
Scandinavian mythology tells of an evil deity named Loki, condemned for the sin of fratricide to lie eternally bound, face upwards, on a rock, receiving the drip of serpent's poison on his face; though his wife ordinarily intercepts the poison with a dish, she occasionally goes aside to empty it, whereupon Loki's agonized writhings become so tremendous as to shake the earth.
In Japan an old legend ascribes earthquakes to the movements of a creature called Jishin-mushi, "earthquake insect", having, as was related by Mr. O. Hattori, to the Asiatic Society of Japan in 1878, an oblong, scaly body, 10 legs, feet like a spider's, and the head of a dragon.
On this head, however, at a place called Kashima, rests the Kaname rock, with which it is the duty of the Kami or deity of the district to keep the creature as quiet as possible.
Hence the old earthquake couplet:-
"No monster can move the Kaname rock,
Though he tug at it never so hard,
For ever it stands, resisting the shock
The Kashima-kami on guard."
Later in history the Jishin-mushi became a monstrous cat-fish.
Next in order come the quasi-scientific theories, or those which, while attributing earthquakes to ordinary operations of nature, do so erroneously, from imperfect knowledge.
Of these the earliest are the views of Aristotle, Pliny, and other Greek writers, who referred earthquakes to the action of subterranean winds.
In China it is said that when the male element, Yang, enters into the earth, the included air, becoming swelled on size, causes earthquakes in its efforts to escape.
The wind theory seems to have been held in England as lately as the middle of the last century, and Shakespeare, in his Henry IV., apparently gave it his support.
To these views succeeded, in the quasi-scientific series, opinions, still stoutly held by some persons, that earthquakes are produced by electrical causes.
In 1760 Dr.Stanley, as well as Percival and Priestly, advocated this theory.
In California many people even now believe that railways, by preventing dangerous electrical accumulations largely reduce the numbers of earthquakes.
The same has been predicted of Japan, but, of course without verification.
That electrical phenomena accompany earthquakes, affecting telegraphic lines and cables, is well known.
In Mauritius earth currents have often been found to precede earthquakes.
Professor Shida, too, has given many instances of earthquakes being accompanied or preceded by abnormal earth-currents; and we may expect to hear more on the subject from a physicist of his ability.
But all evidence and reasoning thus far adduced tend to show that such currents are a consequence rather than a cause of conditions producing earthquakes.
Chemical theories, or those which until 70 or 80 years ago referred earthqakes to violent chemical action brought about by subterranean combinations of such substances as sulphur, vitriel, nitre & c., also belong to the quasi-scientific order on the border-line of which lie the recognition by Dr.Mitchell and Professor Rogers, about the year 1760, of the relation between earthquakes and volcanoes, and their opinions, which first led men to think in the right direction, that the former might be produced by underground movements of steam or lava.
Coming now to the scientific theories of the present day, high probability at least may be claimed for more than one of them.
Doubtless there may be a number of different causes producing earthquakes, at different times and places and under different conditions.
Professor Milne apparently leans to the belief that, while earthquakes may be brought about in very many ways, the two chief processes are faulting-or the breakage of strata while mountains are being tilted up owing to secular cooling of the earth's crust - and underground explosions of steam.
In Switrzerland especially, as well as in India, many of the phenomena are very probably produced by the former of these causes.
The earthquakes of North Eastern Japan, on the other hand, whether accompanied or not by volcanic outbursts, would rather seem to be due to the latter cause.
In this region, lying on the intersection of two great lines of volcanic vents, the earth's crust is, without doubt, intensely hot beneath the surface; and, during the process of elevation that is steadily going on, slight motions may be produced in the heated rocks, which, destroying the statical balance between those rocks and the highly heated vapour of water that has found its way into subterranean recesses, may well allow other water to rush in and flash suddenly into steam, thus producing the shocks of ordinary earthquakes.
To similar action on a grander scale may probably also be attributed such gigantic throes as those which in 1783 caused Asamayama to burst into one of the most tremendous eruptions in the world's history, and which, a century later, blew the top of Krakatoa into fragments.
As for causes apart from secular geological changes, which may be regarded as calculated to disturb the statical balance above referred to, there doubtless are many such factors in the nature of strains and stresses, entering into the production of earthquakes.
Barometric pressure may be one of them; and, although there is little or nothing to encourage a belief that the state of the atmosphere, whether as regards wind, rain, temperature, or sudden changes of pressure, has anything to do with earthquake phenomena, due regard must be given to the arguments in the able paper by Dr. Knott, which was referred to at the beginning of this letter.
In that paper its author shows that, in Japan at least, the frequency of winter earthquakes as compared with those of summer finds a possible explanation in the fact that during winter the average barometric gradient across Japan is much steeper than it is in summer, which coupled with the piling up of snow in the northern regions, may well give rise to long continued stresses tending to produce movements of the earth's crust.
Of subterranean evisceration as a cause of earhquakes little can be said, except that the shocks produced by it are probably very few and of small magnitude.
Though large underground hollows are constantly being formed by such causes as the wasting of limestone or other soluble rocks and the pumping out of salt-springs, experience shows that the giving way at these places is usually slow and gradual.
And even in the case of volcanoes - beneath which, owing to the eruption of enormous masses of matter, large hollows might not unreasonaby be supposed to exist - in Japan, so far from volcanoes being the origin of earthquakes, radiating to all quarters, 80 percent of Japanese earthquakes come along the seaboard, many of them from the sea itself, while the shocks are felt on one side only on a volcano, and the volcanoes themselves are all the time steadily rising.
There remains the theory that periodic tides of the earth's interior matter, may bring about earthquake movements.
Since the final abandonment of the old idea that the earth consists of a comparatively thin crust enclosing a liquid interior-on its having been conclusively shown that this hypothesis is incompatible with known tidal phenomena, as well as with those of precession and nutation - discussion as to the true state of the earth's interior has been mainly divided between those who hold the theory of a solid globe and others who believe that between a solid crust and a solid nucleus is interposed a zone of fluid magma.
With this difference, it appears to be generally agreed that, as shown by Professor G. H. Darwin's classical investigation, the earth, as a whole, possesses at least the rigidity of a ball of glass or of steel, and that the hard outer crust, though certainly flexible to some extent, must be at least from 800 to 1,000 miles thick.
If, however, there be indeed an internal viscous magma, subject to tidal movements, all that can be said is that earthquake statistics as yet fail to furnish any direct evidence on the subject.
Lastly, there is the theory propounded to the French Academy some years ago by M.Delauney, who claimed to have discovered as regards the past that epochs of maximum seismic energy coincided with certain phases of Jupiter and Saturn, and who further formulated the general maxim that periods of earthquake frequency are identical with the times of passage of the earth and planets through the meteoric streams which are known as the Perseids and Leonids.
Whatever may be the value of this hypothesis, its author has at least had the good fortune thus far of finding that his predictions of memorable seismic activity for the years 1883 and 1886 have been most remarkably fulfilled.
On the whole, however, it must be frankly confessed that, of the many existing theories about the agencies which directly give rise to earthquakes, we are not yet in a position to regard any one as conclusive.
All speculation on the question is at present purely conjectural.
Though great strides have been made of late years, and are still in progress, we as yet know too little of the physics of the earth's crust, and of the dynamic forces which have made it what it is and which still continue to modify it.
Rival men of science may dogmatize as they please in favour of this or that interpretation, but the wiser among them are constrained to admit that, as a matter of fact, no exact and positive knowledge of the true causes of earthquakes is yet possessed by any human being.
That further researches will help to a clearer understanding of the problem can hardly be doubted.
And, under this head, the valuable suggestions which have been made from time to time by Professor Milne deserve attentive consideration - notably those for the closest possible observation of all phenomena connected with volcanoes and earthquakes in sensitive regions, including systematic determinations of the magnetic changes going on in live volcanoes, and of the variations of subterranean water-levels, on occasions of earthquakes.
The Times - 1887-Jan. 7th.
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