Artificial Earthquakes

Abstract

PROF. MILNE's experiments with artificial earthquakes in Japan, noticed in NATURE of June 4 (p. 114), show that the vertical free surface-wave had the quickest rate of transit, and this was taken to account for the preliminary tremors of an earthquake. The normal wave travelled with a less velocity, and the transverse wave slowest of all. In the earthquakes which occur here from time to time there are generally, if not always, two distinct shocks felt, and it is possible that the second is the transverse wave following on after the swifter normal vibration. I have not heard that there are any seismographs in the Punjab, and in the alarm of the moment it is not easy to notice the direction of the motion without apparatus; fortunately our earthquakes do not leave any automatic record in the shape of fissures or fallen buildings. But Prof. Milne's experimental results are curiously confirmed by observations in Kashmir during the earthquakes of this month, which do not appear yet to have quite subsided. The Kashmir correspondent of the Lahore Civil and Military Gazette of to-day's date writes as follows:—“The more severe shocks seemed to be followed by others in a different direction, like cross waves. I noticed this in a boat which quivered all over during a severe earthquake, but rolled somewhat afterwards.”