Earthquakes

My daily paperl tells me that yesterday houses were shaken and windows broken in the Plymouth district, owing to earth tremors; and only last week the same paper reported the loss of over a thousand lives and extensi ve destruction of buildings in Coquimbo, Chile, as the result of an earthquake. Having had an extensive experience of .earthquakes, both in Peru· and India, the subject interests me, and, since it may interest others, I am tempted to write this article. Primitive man attributes ground shakings and volcanic activities to the movements of subterranean deities or monsters. Although we do not think so ourselves, still many people have very hazy ideas as to the true nature of these recurring phenomena. That earthquakes and volcanoes occur frequently together in the same country has led to the notion that the latter are the cause of the' former. Such is not the case, though the former may be the cause of a sudden activity in the latter. Residents in India not infrequently experience earthquakes, but they reside many thousands of pliles from any volcano. History reveals many incidents where cities have been destroyed or buried by the eruptions from volcanoes, but few records exist of volcanic earth tremblings having shaken a town to pieces. Careful records show that the world experiences some 60,000 shakings every year. The great majority of these are mere tremors, unappreciated by most people and registered only by sensitive instruments specially designed for the purpose; their duration may be anything from a few seconds to a minute or more. Because the position of the origin 'of these tremors can be traced frequently to or along geological lines of fault, the modern view assumes that earth tremors or earthquakes are the result of slight adjustments or settlements of the earth's superficial crust along those geological lines of fault. Ordinary earth tremors are known technically as microseisms, and they may disturb an area of greater length than breadth. Out of the world's annual crop of earth tremors, about 150 shake the whole of our sphere, or at least disturb a hemisphere. These are what are commonly called earthquakes, but known technically as megaseisms. In the wake of these and originating in the shattered area which they have caused come, during the next few months, the microseisms already mentioned. vVe are not concerned, in this article, so much with these children or followers of the megaseisms as we are with the large originating earthquakes or megaseisms themselves. Few countries are entirely free from one or other of these two classes of earth-disturbance, but both are more frequent in places where the rocks are geologically young, and where we have high mountain ridges with