These waves reach a distant point in the following order: the sound wave through the earth and the great earthquake or shake which produces the damage. Then a smaller sea wave called the forced sea wave. This is followed almost immediately by the sound wave through the sea. Next come the air sound wave and finally the great sea wave; which, rushing in on the shore, sweeps nearly everything before it.
In other words, the disturbances produced by the great earthquake follow in this order of sequence. If, therefore, the great earthquake wave proper transmitted through the earth should for any reason be delayed in reaching a distant place, the great sound waves should be able to give warning of the coming disturbances.
Again, as we have already seen, the earthquake wave is preceded by a number of preliminary tremors, and is followed by a number of after tremors or earthquake echoes. Since, therefore, the preliminary waves reach a place first, it would seem that the approach of an earthquake must be heralded by the preliminary tremors. These, perhaps, at least in part, enable the lower animals to detect its coming.
Again, in almost all instances there are a number of preliminary shocks that precede the great earthquake shock. Some of these preliminary shocks continue at intervals for several days or even longer. Sometimes, indeed, these subterranean sounds fail to be followed by earthquakes. Milne thinks that these sounds are caused by the preliminary tremors which precede the principal shock of the earthquake and that they reach the place first. Here again then it is evident that, were we able to interpret properly these sounds, we would probably be able to foretell the coming quake with a fair degree of certainty.
There would appear to be no reasonable doubt that in some manner which we have not yet been able to discover, but probably along some of the lines indicated above, animals are capable of recognizing a coming earthquake. Long before the coming of the catastrophe they are said to exhibit extreme terror, and in many cases appear to seek the companionship of man, as if for protection.
That the senses of smell and hearing are far more acute in the lower animals than in man no one can reasonably doubt. The manner in which a trained dog can follow a scent, for a long time after the animal or thing producing it has passed, far exceeds the power of scent possessed by man, and it is more than likely that this same power is possessed by all animals who live upon or prey upon other animals. It is probable that faintly odorous vapors or gases escape from the crust shortly before the great shock occurs, and that these faint odors are warnings to the animals of the approaching calamity. The sense of hearing also is much more acute in the lower animals.
Daubeny is evidently of this belief, as will be seen from the following:
"These gases and vapors (alluding to emanations given off from the ground during earthquakes) exert an influence on the barometer, which does appear to be indirectly affected by the earthquake. Then, similar properties also may occasion that uneasiness which animals are said to evince before any such event. Thus, according to the accounts of some writers, rats and mice leave their holes, alligators seek the dry land, quadrupeds snuff the ground, and manifest such signs of the impending calamity that in countries where earthquakes are common, the inhabitants take the alarm in consequence, and escape from their houses. It is right, however, to add, that more recent authorities dispute altogether the correctness of these statements."
Dutton doubts the ability of animals to foretell coming earthquake shocks.
But that the lower animals do exhibit signs of fear at the approach of an earthquake has been repeatedly asserted by good observers.