Seismology

Abstract

Fifty years ago seismology was still in early infancy although a seismoscope to indicate the direction of the maximum movement during earthquakes was known in China 2000 years ago, similar instruments were used in Europe over 200 years ago, and during the eighteenth century the effects of earthquakes were investigated in several instances. About 90 years ago Mallet started his investigations on the mechanics of earthquakes; he suggested better instruments to observe them, tried to determine the wave velocity by using artificial explosions, prepared a catalogue of earthquakes, and developed a fair knowledge of the geographical distribution of epicenters. However, the instruments were too crude to be of real use and recorded only the maximum earth movements. All kinds of observations contained a relatively large percentage of unreliable data as to time and magnitude, and the information available was completely insufficient to support general conclusions; no adequate theoretical knowledge existed. The principal ideas concerning instruments, field observations, theory of earthquake waves, distribution of shocks, the structure of the earth, and the origin of earthquakes (insofar as such ideas exist today) were developed between about 1888 and 1910. Between 1910 and 1930 the fundamental ideas were applied to detailed problems, and the general information was greatly increased, while during the last 10 years improvements in the quality of the observations have enabled us to obtain a higher accuracy in the results. As the last 50 years cover practically the whole history of seismology, only a selection of characteristic developments can be given in limited space. On the other hand seismology comprises so large a number of special fields that it has seemed preferable to review the history of each field separately rather than to attempt the description of the development of all simultaneously.

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