EARTHQUAKES.

Gisborne Times, Volume XXVII, Issue 2572, 5 August 1909, Page 5

EARTHQUAKES.

CABLE NEWS.

FURTHER SHOCKS I H PORTUGAL.

NO DAMAGE DONE

United Puicsa Association-- copyright

LISBON, August 3

Two sharp shocks of earthquake have been experienced in Portugal. No damage was done, but there was a panic at Santarcm.

LATEST THEORIES OF EARTH-

QUAKES

FROM LAST YEAR’S BOOKS

Two books, amongst others,,on earthquakes were published in 1908; and the latest science on the point—as taken from them—was summarised recently in the “Sydney Morning Herald.” The books in question are: “The Physics of Earthquake Phenomena,” by Professor G. G. Knott (1908); “Earthquakes," by Professor W. H. Hobbs, of Michigan University (1908). References were also taken by the “Herald” from Gustave le Bon’s “Evolution of Forces,” William Morris Davis’s “Physical Geography,” and R. A. Proctor’s “Other Suns than Ours.” ‘The prime cause of earthquakes is the instability of the earth’s crust” (Knott). —Rocks a Thick Liquid.— The centre of the earth is liquid, though not the boiling molten cauldron which it used to be thought. The earth begins to become something like a very thick liquid at six miles in depth—in this way. The rock-deep in the earth must be looked on as a pillar supporting the weight of the surface just above it. “Rocks are .... a little less than three times as heavy as . . water. At about six miles beneath the surface the pressure is such that all rocks known to us would be crushed by it. It we attempted to tunnel in rock ... at this depth the roof of the tunnel would immediately collapse, and the opeping bo entirely sealed up. The microscopic pores in the rocks would likewise be closed. Under such conditions the rock could never bo fractured under stress —any more than a liquid could, which flows into any opening as soon as it is made in it—“but would flow much as a thick liquid” (Hobbs). Any cracks on the surface must disappear by the time they reach this liquid, “which has been called the 'zone of flow.’ ” The overlying zone - in which fractures exist is the “zone of fracture. It is this crust of the earth that creases and folds, and sometimes snaps and quakjes. This crust or "zone of fracture.” according to Hobbs, is not in the least the stiff, strong, unsupported crust that it used to be thought It is exceedingly weak and brittle, and full of cracks and faults. It is the thick liquid underneath, which is under the enormous pressure of the mass above it, which has the strength about it. The hot* recks in the intermediate //one, not. quite liquid and yet not full of fissure, arc weak, veaclv to move under uneven pressure. —The Folded Rocks. —

The rocks that come molten from below, the igneous rocks, arc quite obvious in volcanoes and geysers, says Knott. They are not folded rocks. "But the sedimentary rocks, like (sandstones and shale (which were a simple stretch of pebble and sand laid down along the edge of a continent by the action of water and tide) . . . from tho date of their deposition have sunk to form the floor of lakes and seas, and been raised into plateaux aud mountain masses” (Ivnott). They enter on a life of extraordinary vicissitude —are bent, doubled, folded, drawn out, snapped across, and tortured in all kinds of ways.” They are continually sinking and rising in waves centuries long, like, but none the less sure, lie says, the ocean swell. And in this bending and unbending of the earth’s crust there are formed the folded rocks.

—A Fracture.—

‘‘lf during this process fracture occurs, immediately an earthquake shock will be transmitted through the neighboring material.” If one rock face slips against the other a seismic disturbance wi.i take place, which may be felt, sometimes, around the world. In Professor Hobbs’ book there is a picture of such a fault running across a Japanese valley—where ono-lialf of a plain has slipped many feet lower than the other, cutting paths and fields in half. Mountains may take ages to form in this way. But they are being formed even now. In William Morris Davis’s book there is a photograph of certain mountains in Oregon formed comparatively recently.

.—The Ultimate Cause.—

As to where these forces come from which fold and unfold the earth’s crust these very modern boons do not agree. Hobbs quotes Professor Milne, who has noticed that earthquakes happen when the earth’s axis swings out of its old position—which of course would cause certain strains to work about the earth. Knott seems to think that the weight of masses of earth such as the Himalayas (which arc 12 miles above the lowest ocean depths) may have something to do with it. At any rate, lie shows that til© greatest density of rock in Southern Italy and Sicily is just over the line where the great earthquake happened. Gustavo lo Bon thinks the activity of some force like that of radium has something to do with earthquakes. Proctor adopts an interesting theory. He says that it has often boon noticed that hurricanes, storms, depressions follow after earthquakes, and people thought the earthquakes caused, them. But then they also happen before earthquakes. At least the earth has often been noticed ditll and heavy, and the animals are frightened. And probably, lie says, it is the other way ; and what caused the hurricane caused the earthquake too—the passing of a heavy wave of air which was too heavy for the earth’s fractured surface. If the barometer rises half an inch over,lo,ooo square miles (one-sixth the size of England), those square miles have to bear an additional weight of 4,200,000,000 tons of air. If it rises an inch, every foot of. earth bears OoOlb extra, and every square mile 852,000 tons, lake those changes along a sea coast, where the heat and cold and the tides also hole to increase them, and they might well cause' a ■disturbance. All volcanoes except ono in Asia, are near tire sea, he says. ■

the great EARTHQUAKE IX SUMATRA. Messrs Burns, Pliilp, and Co.’s steamer Airlie, which arrived at Sydney on July 21, from 1 ' Java, brought particulars of the great earthquake in West Sumatra, which resulted in heavy loss of life. One report says the earthquake

CABLE NEWS.

was most severely felt in the province of Jambie, South Sumatra, especially in the district of Korinclii. That district lies in a valley in the form, of a triangle. To the north-west is the Peak of Korinchi and Guong Sumbing, both of them active volcanoes. The latter mountain bad lately .been emitting volumes of smoke. The volcanic structure of the country gives every reason for expecting earthquakes, but none of any consequence had been experienced there in the last few years. The earthquake came upon the people of the valley at 1.30 on the morning of June 4. There were repeated shocks, accompanied by a tidal wave. A great many houses collapsed, and fires broke out which wrought great havoc. In all parts of the district, not only houses but also mosques and paddy storehouses had collapsed. The houseless people took refuge in the fields and built temporary shelters. The tidal wave gave rise to landslips and sinking of the ground. The rivers were- blocked and overflowed their banks. Great damage was done to roads and fridges. Several sulphur springs are active, while others have dried up. Up to the date of last ad : vices the number of persons killed by the shocks is set at 230. On the West Coast of Sumatra the shocks were heavy enough to start a panic, and the sea, too, showed signs of great disturbance.