EARTHQUAKES.

Rangitikei Advocate and Manawatu Argus, Volume XXXIV, Issue 9336, 4 January 1909, Page 2

EARTHQUAKES.

SOME INTERESTING OBSERVATIONS. Avoiding all technicalities, and speaking as far as possible from the popular standpoint, Mr G. Hogbeu, Inspector-General of Schools, Who has made a close study of earthquakes and their causes, had some interesting remarks to make on this subject when questioned on W eclnesday by a Times,reporter. “People," said Mr Hogben ‘ connect* earthquakes with volcanic action,, but there is only a small class of earthquakes caused by such action, in the same way that an explosion in a mine would cause a shaking of the earth. These, however, are generally of a local character, and do . not cover a wide area, for instance, the earthquakes at Rotorua at the ' time of the eruption in 1886. and those at Whakatane lately, were 9*; that description, and were not felt far away. These were due to the explosion of steamjand other gases, but they were not earthquakes ox the kind that make big disturbances; they are entirely different. PRIMARY CAUSES.

‘“lt may be said that there are two primary causes of earthquakes. One is the unequal shrinkage of layers of tbe earth’s crust. The consequence of that is that rooks nearer to the surface are really too large to occupy the apace they would naturally fall into as the inner part of the crust shrinks. Therefore, the outer crust must crumble and become contorted in various ways in order to repack itself; it has got to repack itself according to the space available. That repacking generally takes place about certain lines or planes, usually called axes. This movement of repacking leads to the movement of the rooks along the axes or parallel to them, forming various kinds ot faults. “ This fault movement that takes place is generally very small, but now and then there is a little bility opposition, and there will be sudden movements. That gives rise to vibrations of different kinds which go over the whole of toe earth’s crust, if the movement is at all considerable. These vibrations we call .earthquakes, which may produce secondary effects, throwing down rocks that may open chasms, and in their train bringing down buildings, etc. Nearly all these results are secondary. Thus what people know as earthquakes afe nearly ail secondary results. 0f course, sometimes itjhappens that & place is on an actual mass that is moved. That is not secondary. For instance, in 1855 in Wellington the actually moving mass reached right up to the surface, and raised the land surface around Wellington higher. That was not secondary, hut primary, THE LAND AND SEA.

“As to the other cause: That is going on wherever there is land or sea, to a certain extent, but it is not always sufficient to cause earthquakes. In the * natural course of things the land surface is denuded by rainfall, snow, glaciers, etc., and part of it always being worn away and carried by the rivers into the sea. This is constantly going on. The roeks below the land and the rocks below* the sea are all being pressed upon by what is above them. If yon take the pressure off the land and put it on to the sea bed yon remove the pressure on the rooks underlying the land and increase the pressure on the rooks underlying the ocean bed. That will make the land rise and the ocean bed sink. The result is distortion and ultimate dislocation near the junction of the sea and land, frequently followed by the formation of a monoolinal fault. The movement of that fault _at times when it is sudden would give rise to vibrations which are the primary phenomena of earthquakes. CONNECTION OF EARTHQUAKES.

“I don’t say it is utterly impossible that an earthquake happening at a distance oonld have connection with an earthquake taking place, here, say, at perhaps the same time. That would be a rash statement to make, but they have never been shown to have any distinct connection. There are about 15,000 earthquakes actually recorded every year throughout the world, pretty well distributed in regard to time, but any idea that they are connected With one another, or that they are connected with phases of the moon, tides, sun-spots, eto., is not borne out by facts.

EARTHQUAKES NOT IMPORTED “No, we manufacture on the spot. We don’t import them from Italy, South America, or elsewhere. It is the adjustment that is going on below this part of the Pacific that is entirely responsible for the. earthquakes here. There is not even any connection between ourselves. South Australia, and Tasmania in this repseot. I have studied this question for many years. I cannot find a single piece of evidence to bear out such a contention, and I have examined closely into every earthquake that has occurred in the Facfiio for the last twenty years. Anyone who wonld say there was any possible connection is rather going beyond his facts. Some people think that earthquakes come from sultry weather, for instance. OTHER EXPERIENCES.

“In regard to the Mount Pelee eruption, in 1903, you will recollect that it was preceded by seven earthquake shocks, the first being felt at Guatemala, others following between April and May, in the Caribbean Sea, to the west of St. Vincent and Martinique, followed by the eruption of La Soufriere, aada small eruption of Mount Pelee. On May Btb, just before the big eruption, there was another earthquake movement right on the axis on which Mount Pelee is situated. This Series would be the folding movements of . the earth , quakes, beginning with the western mass and ending in the east on the axis on which Mount Pelee stood, and on the west side of which La Soufriere stood. The probability is that this folding relieved the strain of the rocks and allowed the accumulated steam and other gases to find vent because of that relief. That is my theory of it, and the theory of others. It is rather significant that other eruptions in the same region have been preceded by similar folding movements and earthquakes to the westward, so it looks as if in that part of the world the earthquakes had indirectly caused the eruption. The steam was there before, but the pressure was relieved id consequence of the movements which caused the earthquakes. CAUSE OF THE PRESENT SHOOK. “As to the cause'of the present

earthquake in Italy, without fuller details, it can only be surmised, but the probability is that it was due to a fault movement along the axis of Calabria. Taking the world fgenerally, the evidence of the relation between fault movements and earthquakes is pretty convincing. ’ ’ The earthquake in Italy, through unavoidable circumstances, was not recorded onMr Hogben’s instrument, but Mr Hogben is confident that it was recorded in Christchurch.