Earthquakes

Abstract

IN the introduction to his little volume on earthquakes, Prof. Fouqué observes very justly that it is only in recent years that seismology has begun to shape itself to the lines of an exact science. Its students have of late concentrated their attention on questions susceptible of direct attack by observation and experiment. The older seismologists made the mistake of attempting to take the citadel, by storm, and failed. The younger school of investigators, proceeding more gradually, have at least succeeded in showing how enormously complex the problem of earthquakes in their origin and propagation really is. The older seismologists were for the most part men with little knowledge of mechanics, and their fundamental mistake was that they under-estimated the difficulty of the problem in its mechanical aspect. Setting to work with a preconceived and quite false idea of its simplicity, they used such observational data as were at their disposal to build up an elaborate structure of inference and hypothesis— a structure very ill adapted to bear the shock of the first earthquake that formed the object of scientific measurement. The foundation on which the new school builds its science is exact seismometry; and so far, little, if anything, more than the foundation is laid. It is less than ten years since instruments of precision were introduced, capable of giving complete information as to the manner of motion of the ground. We now have sufficiently full and exact knowledge of the nature of the motion which takes place at one or another point of the earth's surface in the affected region while an earthquake is going on. The elaborate recording seismographs which have been brought to something like perfection by a few enthusiastic workers in Japan have analyzed this motion as completely as can be desired. But beyond this we as yet know next to nothing with any certainty about the real character of an earthquake. The relation which exists between the motion at one point and that at another, the manner of the motion below the surface, the transformations which the seismic waves undergo en route, are subjects hardly touched; and no seismometric observations have as yet been made, in a single case, from which conclusions may be drawn with any certainty as to the position of the origin and the nature of the originating disturbance. These are matters which used to be glibly settled by reference to a few projected stones or cracked walls, or to the stoppage of some village clocks: if the new seismometry has not yet thrown much light on them, it has at least shown how gross was the former darkness.

Les Tremblements de Terre.

Par F. Fouqué, Membre de l'Institut (Académie des Sciences), Professeur au Collège de France. (Paris: J. B. Baillière et Fils, 1888.)