After flood, fire, earthquake, or when opportunity presents itself, changes are introduced in the construction of ordinary buildings. In a so-called earthquake-proof house, although externally it is similar to other dwellings, we find rafters running from the ridge pole to the floor sills, an exceedingly light roof, iron straps and sockets replacing mortices and tenons, and many other departures from ordinary rules. Masonry arches for bridges or arched openings in walls (unless protected by lintels), heavy gables, ornamental copings, cappings for chimneys, have by their repeated failure shown that they are undesirable features for construction in earthquake countries. As sites for buildings it is well to avoid soft ground, on which the movement is always greater than on hard ground. Excessive movement also takes place along the face of unsupported openings, and for this reason the edges of scarps, bluffs, cuttings and river-banks are localities to be avoided. In short, the rules and precautions which have to be recognized so as to avoid or mitigate the effects of earthquake movement are so numerous that students of engineering and architecture in Japan receive a special course of lectures on this subject. When it is remembered that a large earthquake may entail a loss of life greater than that which takes place in many wars, and that for the reconstruction of ordinary buildings, factories and public works an expenditure of several million pounds sterling is required, the importance of these studies cannot be overrated. Severe earthquakes are fortunately unknown in the British Isles, but we have simply to turn our eyes to earthquake-shaken colonies and lands in close commercial touch with Great Britain to realize the importance of mitigating such disasters as much as possible, and any endeavour to obviate the wholesale destruction of life should appeal to the civilized communities of the world.
An unexpected application of seismometry has been to record the vibration of railway trains, bridges and steamships. An instrument of suitable construction will give records of the more or less violent jolting and vibratory Applications of seismometry. movements of a train, and so localize irregularities due to changes in the character of ballast and sleepers, to variation in gauge, &c. An instrument placed on a locomotive throws considerable light upon the effects due to the methods of balancing the wheels, and by alterations in this respect a saving of fuel of from 1 to 5 ℔ of coal per mile per locomotive has sometimes been effected.
By mapping the centres from which earthquakes originate off the coast of Japan, we have not only determined districts where geological activity is pronounced, but have placed before the cable engineer well-defined localities which it is advisable to avoid; and in the records of unfelt earthquakes which originate far from land similar information is being collected for the deeper parts of the oceans. Occasionally these records have almost immediately made clear the cause of a cable failure. From lack of such information in 1888, when the cables connecting Australia with the outer world were simultaneously broken, the sudden isolation was regarded as a possible operation of war, and the colonists called out their naval and military reserves. Records of earthquakes originating at great distances have also frequently enabled us to anticipate, to correct, to extend, or to disprove telegraphic accounts of the disasters. Whatever information a seismogram may give is certain, whilst the information gathered from telegrams may in the process of transit become exaggerated or minimized. Otherwise unaccountable disturbances in records from magnetographs, barographs and other instruments employed in observatories are frequently explained by reference to the traces yielded by seismometers. Perhaps the greatest triumph in seismological investigation has been the determination of the varying rates at which motion is propagated through the world. These measurements have already thrown new light upon its effective rigidity, and if we assume that the density of the earth increases uniformly from its surface towards its centre, so that its mean density is 5.5, then, according to Knott, the coefficient of elasticity which governs the transmission of preliminary tremors of an earthquake increases at a rate of nearly 1.2% per mile of descent.
(J. Mi.)
Authorities.—J. Milne, Seismology (London, 1898), Earthquakes (London, 1898), Bakerian Lecture, “Recent Advances in Seismology,” Proc. Roy. Soc., 1906, 77, p. 365; J.A. Ewing, Memoir on Earthquake Measurement (Tokyo, 1883); C.E. Dutton, Earthquakes in the Light of the New Seismology (London, 1904); “The Charleston Earthquake of Aug. 31, 1886,” Ninth Annual Report of the United States Geological Survey, 1889; W.H. Hobbs, Earthquakes, an Introduction to Seismic Geology (London, 1908), “The San Francisco Earthquake and Fire, 1906,” Bull. U.S. Geol. Surv. No. 324; “The California Earthquake of Ap. 18, 1906,” Rep. State Earthq. Com. (Washington, D.C., 1908); R.D. Oldham, “Report on the Great Earthquake of 12 June 1897,” Mem. Geol. Surv. India, xxix. 1899, “On the Propagation of Earthquake Motion to great Distances,” Phil. Trans., 1900, A, vol. 194, p. 135, “The Constitution of the Interior of the Earth as revealed by Earthquakes,” Quar. Jour. Geol. Soc., 1906, 62, p. 456; 1907, 63, p. 344; C. Davison, A Study of Recent Earthquakes (London, 1905); The Hereford Earthquake of December 17, 1896 (Birmingham, 1899), “The Investigation of Earthquakes,” Beiträge z. Geophysik, Bd. ix., 1908, p. 201, and papers on British earthquakes in Quart. Jour. Geol. Soc.; T.J.J. See, “The Cause of Earthquakes, Mountain Formation and Kindred Phenomena connected with the Physics of the Earth,” Proc. Amer. Phil. Soc., 1906, 45, p. 273; F. Frech, “Erdbeben und Gebirgsbau,” Petermann’s Mitteilungen, Bd. 53, 1907, p. 245 (with maps); C.G. Knott, The Physics of Earthquake Phenomena (Oxford, 1908); Comte F. de Montessus de Ballore, Les Tremblements de terre: géographie séismologique (Paris, 1906), La Science séismologique (1907); Transactions of the Seismological Society of Japan; Seismological Journal (Yokohama); Bollettino della Società Sismologica Italiana (Rome); Reports of the British Association, containing the annual reports of the Committee for Seismological Investigations; papers in the Beiträge zur Geophysik and the Ergänzungsbände.
[1] The publications for 1880-1892 were termed the Transactions of the Seismological Society of Japan, and for 1893-1895 the Seismological Journal of Japan. The observations are now published by the Earthquake Investigation Committee of Japan, and edited by F. Omori, professor of seismology at the university of Tokyo.
[2] The chief Italian station is at Rocca di Papa near Rome. It is equipped with delicate instruments designed by its director, Giovanni Agamennone. The records since 1895 are published in the Bollettino della Società Sismologica Italiana, edited by Luigi Palazzo, director of the Central Office for Meteorology and Geodynamics at Rome.
[3] The chief Austrian publications are:—Mittheilungen der Erdbebencommission der k. Akad. der Wissen. in Wien (since 1897); Die Erdbebenwarte (1901-1907); and the “Neueste Erdbebennachrichten, Beilage der Monatsschrift Die Erdbebenwarte.”
[4] The “International Seismological Association” was founded at Strassburg in 1903, and publishes the Beiträge zur Geophysik, edited by George Gerland, director of the Strassburg station; the papers are printed in several languages.