EARTHQUAKES.

Temuka Leader, Issue 10462, 26 October 1929, Page 3

EARTHQUAKES.

A RECENT DISCOVERY. OCEAN SECRETS. TREMENDOUS DEPTHS. The Fleming Deep, between Guam and Japan, discovered recently by scientists, may hold the secret of recent tremors in many lands. Another hole in the bottom of the sea has recently, been discovered —a trough-like valley lying five and ahalf miles beneath the surface of the Pacific Ocean, between Japan and Guam. This deep is interesting to science because it probably is a mother of earthquakes. Early in June the Carnegie Institution’s non-magnetic survey yacht Carnegie, after taking soundings on the floor of the Pacific, reported that an ocean deep hitherto unknown had been found in latitude 23.8 degrees north and longtitude 144.1 degrees east, a lonely part of the ocean about 1400 miles to the south-east of Tokyo. According to wireless messages from the Carnegie the deep measures 28,380 ft and is about nine miles wide.

The changing readings of an interesting instrument on board the vessel were indicating the first story of the presence of this inverted mountain range under the sea. The sonic depth-finder measures the length of time it takes sound to travel from the surface of the water to the bottom and the return of its echo to the surface. From this time interval the depth of the water may be determined —the longer the time the deeper the water. As the ship moved up the Pacific some 1400 miles from Japan on its course from Guam, the instrument had shown the ocean bottom to be 13,200 ft below for a distance of 106 miles. Then the floor of the ocean dropped to 19,S00ft for a distance of 47 miles. Again it dropped to 26,400 ft for a distance of 20 miles, and finally to 28,3 SO ft for a distance of nine miles. That meant a tremendous hole in the sea, into which high mountain peaks could be tumbled and even then lie submerged more than two and a-half miles beneath the surface of the ocean. Even mighty Everest itself, the highest mountain on the globe, would be only an insignificant hillock protruding from the surface of the Pacific to a height of 761 ft.

The new deep was named in honour of John A. Fleming, assistantdirector of the department of terrestrial magnetism of the Carnegie Institution of Washington, by Captain Ault, of the Carnegie, following the custom of naming such depths after scientists.

“We do not yet know a great deal about the new deep,” Mr Fleming said, “as we ha-ve not received the detailed report of the soundings. Nor has anyone had time to study the deep in its relationship to the epicentres of previously recorded earthquakes. “We do not know that the deep is a fault or crack in the earth’s crust along which stresses and strains cause adjustments of the crust which manifest themselves as earthquakes.” Down in this region of perpetual night, where the only light is the ghostlike gleams of fish who carry their own lanterns, where the temperature always hovers around freezing point and the pressure is great that it would crush a steel safe as flat as a flounder, the earth’s crust is folded in ridges, as it is in the mountain ranges on land. Such deep folds mean that the rocks in the crust are faulted or broken, and from time to time, because of the great pressure, the broken faces of the rocks shift. When the earth beneath the sea does slip or slide, the vibrations it sets up cast down the cities of men on the mainland of Asia or in the islands of the Pacific. What do these great troughs in the ocean look like?

We have only the description of them, writes Nell Ray Clarke, in the San Francisco “Chronicle,” as it is written by the depth-finder and fragmentary bits of information about the bottom and. the life that exists there told by dredging operations along the ocean bottom. The deeps are huge furrows, sometimes long, sometimes comparatively short and relatively narrow. The area in the Pacific to the east of Japan must look like huge corrugations along the ocean bottom.

The cold water from the Northern oceans drops down to the floor of the other oceans and keeps the temperature in the abysses hovering around the freezing point. It is cold, black, calm and silent down there. But life of some sort must exist at such depths as the Fleming Deep. Protozoa, sponges, corals, worms, moluscs, crustaceans and fish have been brought up from very deep parts of the ocean bottom. Perpetual night reigns undisturbed by even a faint sheen of light from above. The queer undersea life must move about by the phosphorescent gleams from their antennae.

They are able to exist at such tremendous pressures because their tissues are permeated by fluids under the same pressure and are consequently supported equally on the inside and the outside. When such animals are brought suddenly from their native haunts, their eyes burst outward, their scales are ripped off and other parts of their bodies are horribly distorted. [The significance of the discovery

of the new deep is the relationship that it may bear to the occurrence

of earthquakes in Japan and other islands of the Pacific. A number of the most disastrous earthquakes in the world’s history have been accompanied by significant recorded changes in the depth of the ocean bed somewhere nearby. At least some of the breaks in trans-oceanic cables may be attributed to disturbances on the ocean beds. In fact, it is now pretty generally accepted that most earthquakes originate under the sea.

According to geologists, when the earth cooled millions of years ago, it shrank. Its already cooler outer crust folded into mountains and valleys on land and into depressions and elevations beneath the ' sea. Where the folds are highest and deepest, the strata of rocks have been tilted and broken, and there the stress is the greatest. Friction alone holds the parts together. Even the hardest rock is somewhat plastic, and when the stress becomes too great the earth growls and shakes.

The most unstable of all the regions of the earth is the bed of the Pacific Ocean to the east of Japan. Here the bed is cast into great downward folds, making the deepest spots in the oceans yet known to man. There are five known deeps greater than the Fleming Deep recently discovered by the Carnegie. They are the Mindanao Deep, off Mindanao of the Philippines, measuring 34,220 ft, which was discovered by the German ship Emden in 1927. It Is the deepest deep in the ocean which is yet known. In it the highest mountain on earth could be buried to a depth of almost a mile. The others follow in the order of. their magnitude: The Tuscarora, or Japan Deep, lying 145 miles south-east of Tokyo, is 32,644 ft deep. It is believed to have been the centre of the most disastrous earthquake within recent years—that in Japan on September 1, 1923. The Mariana Deep, off Guam, is 31,000 ft. The Kerma dec, or Aldrich Deep, 300 miles north-east of New Zealand, is 31,000 ft. The Solomon Deep, off the Solomon Islands, is 30,000 ft, and the Fleming Deep is 28,'3 8 Oft. The Atlantic Ocean bed, which is geologically older than the Pacific, has only one deep approaching in depth those of the Pacific. During the last 1400 years Japan has experienced at least 225 earthquakes, each of which has taken a great toll of lives. There seems little reason to doubt that the major portion of them originated in that deeply folded section of the Pacific to the east of the islands, where the ocean bottom plunges downward as if it were seeking the centre of the earth. Geologists have expressed the belief that the formation of wrinkles in the crust of the earth beneath the Pacific in the region of Japan has not yet ceased —that changes in the contours of the land are still in progress. They believe that the deeps are getting deeper and narrower and that the bed of the ocean may really be cracked. It is now believed that those earthquakes which occur in regions where volcanoes are abundant are for the most part local in character. Furthermore, the most violent earthquakes are abundant in regions which are non-volcanic, and therefore some other explanation of their occurrence must be looked for. The severest earthquakes in Europe have not taken place around Mount Etna, but in the vicinity of the Apennines and the Alps. The tremendous explosions of Krakatoa in 1883 and of Bandaisan in 1888, although they were felt ovex* a tremendous area, were accompanied only by earthquakes which could be considered purely local in origin. In the main island of the Japanese group the earth actually cracked open for a distance of 66 miles during the famous earthquake of 1891. One side of the earth along the crack dropped 20ft below the 1 side which remained at its old level. The Fleming Deep is simply another of Mother Earth’s wrinkles that we are just learning about. If ever the old lady decides to give a wriggle oi - a twitch, man is likely to suffer.