EARTHQUAKE CAUSES

Evening Star, Issue 22070, 2 July 1935, Page 11

EARTHQUAKE CAUSES

vm mm zones WHEN MOUNTAINS “ SETTLE ” I'he recent Formosa disaster provides strong support for the belief that the world’s major earthquakes occur in two well-defined belts, corresponding with the greatest mountain chains, states a scientific correspondent of the ‘ Morning Post,' London. One of these bolts, which sprawls across the whole width of Europe and Asia, has been credited with 53 per cont. out of ft world catalogue ©f 160,000 earthquakes. It follows the line represented by the Pyrenees, the Alps, the Himalayas, and Malaya. The other, which, according to the same survey, contributes 38 per Cent, of the world's earthquakes, stretches in ft semi-circle round the Pacific;; Following the lino of the Andes and the Rocky Mountains up the west coast of America, it passes through Japan, Formosa, and the Philippine Islands. It then curves back east and south across the Pacific until it reaches New Zealand. SUBMERGED PEAKS. Many of the mountains responsible for this Pacific zone are partly or wholly submerged. Japan owes most of het earthquake troubles to the Tuscnrora deep, off its Pacific coast, .which reaches almost as far below sea level as Mount Everest towers above it. Formosa *is in similarly dangerous proximity to the Philippine deep. From the top of Nutakayalna, the highest point of the island, the ground level drops no less than 31,600 ft within 160 miles, and the steepest part of the slope is relatively near Formosa. The case of the Totlgah and Kerraadcc Islands, between Samoa and New Zealand, is oven more Striking. Each of these smaller groups rises sharply from ocean deeps of the same names. The greatest depth is about 30,000 ft in both Cases. < MOVEMENT SURPRISINGLY SMALL. The theory is that a state of strain inevitably results from the uprearingof any big mountain chain, From this point of view it is immaterial whether the mountains are wholly or partly beneath the seji. As the great mast of the mountains gradually settles down the strain increases, until at some point or other breaking point is reached. There is a slight slipping of two rock surfaces and the earth over a wide area is shaken to and fro, as the ends of a long stick vibrato when the stick is broken in the middle. In relation to the damage done the earth movement may be surprisingly small. A movement of less than a thousandth of an inch can be felt; and the greatest up-and-down movement which has ever taken place was one of only four inches in the Japanese earthquake in 1891. During the same earthquake the sideways movement reached Min.