Go to National Library of New Zealand Te Puna Mātauranga o Aotearoa
Volume 26, 1893
– 637 –

Earthquakes.

The question has been asked, Are there any peculiar meteorological conditions of the atmosphere which are connected with earthquakes? And lately the subject was discussed here with reference to wind. It did not appear that wind and earthquakes were directly connected, although it has been observed on several occasions in New Zealand that, when it has been blowing hard at the time of an earthquake, the wind ceased during the short period occupied by the shock or shocks, and then burst forth again. Possibly this effect may have been due to the rapidly-moving earth-waves having retarded, for a time, the motion of the air in contact with the surface of the earth, the directions of motion having happened to be opposite; and the subject is worthy of further investigation. But in some parts of the world it has been noticed that previous to an earthquake there has been a peculiar condition of the atmosphere, similar to that preceding a thunderstorm, causing disquietude to animals and giving warning to men, and that this condition of the atmosphere has disappeared immediately after the earthquake. I have not been able to trace any record of such a condition of the atmosphere having been noticed in connection with earthquakes in New Zealand, but in California it is a well-recognised phenomenon, and I believed it has been observed in other countries. It has occurred to me that the explanation may be found in the geological conformation of the country where this phenomenon has been observed, together with the facts that are known concerning thermo-electric batteries and electrical induction. If the geological structure of the ground underlying great plains be horizontal strata of varying materials, and in which either the lower strata are more heated than the upper strata, according to the known laws of increase of temperature with increased depth below the earth's surface,—or in which the upper surface is excessively heated by the sun,—then we may have the conditions required for the production of great elec-

– 638 –

trical tension between the upper and lower strata, if some of the intermediate strata have become so dry as to cease to be conductors, and so are unable to relieve this tension quietly and gradually. This state of electric tension at the earth's surface would, by induction, cause a contrary electric condition in the lower strata of the atmosphere, and the peculiar meteorological effects referred to would be experienced. When the electric tension between the upper and inferior strata became so great that a subterranean electric discharge took place between them, equilibrium would be restored and the atmospheric disturbance due to induction would cease. The subterranean electric discharge would cause so great a shock as to produce the effects of the earthquake, probably by setting in action the potential energy stored up by the gradual cooling of the earth, and tending to produce shrinkage, crushing, and crumpling, and so unequal stress. Owing to the great contortions to which the strata have been subjected in the greater part of New Zealand, the conditions are perhaps not to be found here which would give rise to the phenomenon of such a subterraneous electric disturbance as above suggested; but in the great wheat-growing plains of California, where the premonitory atmospheric warning of an impending earthquake has been noticed, they probably do exist. It is possible that they may also exist in the great Canterbury plains, and it would be of interest to note whether any such premonitory symptoms are ever observed there previous to earthquake shocks.