III. On the propagation of earthquake motion to great distances

Abstract

1. The earliest suggestion of the existence of more than one kind of wave motion in an earthquake appears to have been made in 1849 by Wertheim. After discussing on theoretical grounds the ratio between the rates of propagation of distortional and condensational waves in an infinite solid, he proceeds to say that the only possible experimental verification would be by the use of a very large body, such as the Earth itself. It would hardly be possible to produce, artificially, a disturbance which would be propagated and be sensible at a great distance from the origin, but such disturbances are produced naturally in earthquakes, and he finds in the descriptions of great earthquakes indications of two distinct types of disturbance, which succeed each other in point of time, and which he attributes to the two forms of elastic wave motion. Suggestive as it is, this memoir seems for long to have been devoid of influence on seismological research. It would not be materially incorrect to say that Robert Mallet’s classic works were based on the hypothesis that earthquake motion was solely that of a condensational wave.