Earthquakes.

Progress, Volume IV, Issue 5, 1 March 1909, Page 170

Earthquakes.

Of the earthquake fact there is no doubt of any kind. It shakes you and everything in which you are interested. Sometimes there is a mere tremor with a light scare like a catch in the breath. Sometimes cities are devastated and men crushed to death by the thousand ; and occasionally districts are engulphed by the sea. But scare or terror, disturbance or death, the earthquake is unmistakeable. Of the causes of the earthquake there is much discussion. Science wanders among many explanations. Once upon a time all scientific men regarded earthquakes as due to volcanic action, and it is a fact as undoubted as the earthquake itself that where there are volcanoes there are earthquakes. It seems to many, therefore, safe to conclude that many earthquakes are due to volcanic action. At the same time the earth has certainly quaked in places where nothing is known of volcanic action. This fact has led to the evolution of the pressure theory. According to this, the weight of various parts of the earth's crust is changing. Denudation deprives the mountains of great weights, which are piled up on the sea bottom or other convenient place, until the weight crushes the supporting rocks below, when there is subsidence and cracking of the surface, otherwise earthquakes. Speaking of the great Sicilian-Califor-nian earthquake, Professor Suess, of Vienna, throws the whole weight of geological science on a disc of the earth 's crust, which comprises the stricken country, and makes that disc sink down steadily towards the subterranean fires. He cheerfully remarks that when the sinking process is complete, "the hills of Scylla and a great part of the Peloritan Range, near Messina, will be below the water; the Strait of Messina will be widened, and only a fragment of the Eastern Sicilian hills will project from the sea." Here is a man who, in a manner of speaking, sees a great round piece of the earth's crust being let down by chains, of which he has measured the length, and knows how much still remains to run out. Otherwise his announcement that certain parts will not be lost might be put down to sheer good nature. In addition, we have the moon theory and the sun theory. According to the first the proximity of the moon shakes up the nearest part of the earth's crust, as happened at Whakatane not long ago. According to the second, the spots in the sun are caused by the upleap of fiery tongues, springing many thousand miles into space. These tremendous manifestations of energy set the ether of space vibrating. These vibrations of either shock one another through space, 95 millions of miles of it, in eight minutes, the last vibration beating in the nearest part of the earth's crust. "When the sun spots are at maximum, these demolitions here below take place in the Northern Hemisphere, and when they are at a minimum the Southern suffers. The North has just undergone its ordeal; soon it will be the turn of the South. Mr. Wragge. to whom we owe this theory, does not want to frighten us, but he feels bound to tell the truth, which, as he sees it, is that the minimum of sun spots being at hand, the Southern Hemisphere must be prepared for the maximum of earthquakes. Now, according to his immediate predeces-

sor in causation, the propinquity of the moon is making things generally unstable for the South also. On the whole, we may be said to be forewarned. True, Mr. Wragge's theory seems to topple when looked at closely. It does, for instance, appear incomprehensible why, if the shock of the last vibration makes the earthquake, the buildings are not flattened before the collapse of the earth which carries them. Neither does it seem quite likely that the smaller vibrations of the minimum period of sun disturbance should work the havoc in one hemisphere which in the other requires the larger pulsations of the maximum epoch. Further, as ether is of its nature etherial, not material like the air. it is not easy to see how it can be made to vibrate, except in the mind of fancy. As to the moon theory, there does not seem to be much more than coincidence as yet — a thing strong enough rather to suggest inquiry on a certain line, than to justify dogmatic conclusion. Therefore the forewarnings do not seem to be as important as they are in the minds of those who have raised them. After all, there can be no prevention. When the seismologist predicts an earthquake with the same percentage of certainty as a meteorologist predicts a storm, we shall have to put up with the earthquake as we have to put up with the storm. The best forewarners are the earthquakes of the past. Seismology claims that the records of the seismograph are very valuable, but that claim has been made good only so far as they refer to the past. No one has as yet pretended that the arrival of an earthquake at a given spot can be calculated from earthquake data, as the approach of a storm is calculated from the appearance of that storm at various points of a path usually followed in obedience to the law of storms. Before seismology gets so far, mankind must be content with the fact that the first time we know an earthquake is when it shakes us. Where this has happened it may happen again; sometimes, indeed, a quake comes in a place quite unexpected, as the great earthquake of Lisbon did; generally there are zones of earthquakes coinciding with zones of volcanic activity. The precautions to be taken depend on these facts. Just as in the islands of the Tropics, where there is a hurricane season, men build houses that it is not easy to blow down, so in countries of earthquake visitation men ought to build dwellings that may not be shaken down. San Francisco has recorded that steel frames and ferro-concrete are capital earthquake resisters, and that a certain class of materials is the right thing for discouraging the fire that comes after earthquake disasters. Here are the lessons of experience for men to follow everywhere. Scientific observation has, it is claimed, established that in every earthquake there are certain areas left untouched. Men are warned to confine their buildings to such areas. It looks as if one were to say an earthquake is like a hand with extended fingers, which leaves undisturbed all the space between the fingers, and to advise that the building sites of the future be confined to these spared spaces. But who will guarantee that the hand will at the next impact strike the same place? Still, it can at least do no harm to confine buildings to such sites, and as this is, after all, the region of the unknown, there may be some chance of immunity. The best chance is, of course, to go and live in a non-earthquake country.

But that being impossible, the next best thing is to build suitably, reducing risk to the minimum; and that policy can not be thwarted by the choice of a once spared locality. The losses in earthquakes are, of course, terrible, and the horrors appalling. But there are greater losses and horrors more widespread m other directions. For example, millions perish periodically whenever the great Yellow River, whose bottom has long been raised by silt above the level of the Yang-tse valley, bursts its banks; and the Plague in Hindustan carries off annually several millions of people. In comparison with these disasters, the quarter million victims of the Messina catastrophe sink into comparative insignificance. It is the first time that docks and similar valuable property have been destroyed. But that is because the people who, like the Chinese returning to the low plains for the sake of the fertility added by the inundation, build flimsily. This very return proves also that men will return to the most dangerous sites when business calls them or profit attracts them. The moral of the Messina story, then, is not to grieve too much, to send what help we can afford to the survivors, and advise them to rebuild on the lines of proved earthquake stability, in the hope that the worst may not happen in the shape of subsidences of the land or submergings by the sea. These are the unavoidable risks of earthquake countries. The others may be minimised into the comparatively easily endurable.