CAUSE OF THE ’QUAKES.

Putaruru Press, Volume IV, Issue 160, 25 November 1926, Page 5

CAUSE OF THE ’QUAKES.

THEORY OF SUBSIDENCE DISPUTED.

So far the theories expressed as to the cause of the earthquakes at Morrinsville have been to the effect that a subsidence of the earth’s crust has taken place. Quite a different opinion, however, based on engineering principles, is advanced by Mr. P. J. Cooper, of Morrinsville, who holds that the sharp jolts were caused by what is known among engineers as “ water hammer.”

“ The shocks that Morrinsville has been having are due to explosions,” said Mr. Cooper, when discussing the matter the other day. “ There is no evidence of subsidence or of the ground being subjected to a rolling motion similar to the waves of the sea. An explosion will always show the result at the weakest spot; I mention this because it bears on what follows:

“ The only explanation, seeing that it is agreed the shakes are not of a volcanic nature, is that under Morrinsville there is a stream, or it may be of such dimensions as to be called a river. Now, these streams come near the surface at places and at others they are very deep. When this water finds its way down a fault in the earth’s surface, and this fault extends down to where the heat is terrific, the result is an explosion when millions of horse power are generated instantly. This hits the incoming water with the result that the tremendous jolt is transmitted to the weakest spot and is made to "heave and tremble in an alarming manner. At the spot where the water caused the explosion (which in Morrinsville's case may be many miles away) thousands of tons of earth would be displaced, closing the fault, and the stream would go on its way, although somewhat diverted. “ The subsequent smaller explosions would be due to the water percolating the newly fallen earth. These explosions would naturally become less severe as the filling became consolidated.” By way of further explanation, Mr. Cooper said it was well known what the effect would be to throw a cup of water on to a good fire in . the range, at the same time closing the door of the grate. The effect was the same as what had gone on down below, except in one case the explosion is confined, while in the other the stove suffers. He gave another illustration of a pipe, no matter of what length, one end red hot and filled suddenly with water. An explosion would result at the hot end, gushing the watef out the other end with terrible force, and if this end was against a brick wall he would be sorry for the brick wall. This force of water caused by an explosion is what is known to - engineers as “ water hammer.”

Discussing- the severity of the shakes, Mr. Cooper said' he estimated that the “ water hammer ”~st'ruck the earth at Morrinsville about 100 ft to 150 ft below the surface. Had' the distance been greater the shocks would have been deadened somewhat by the time they reached' the surface, but would, have been felt over a much wider area.

The explanation as to varying directions from which the shakes appeared to come was that small fissures had been opened up off the main subterranean waterway and shocks would he felt from these from time to time. Mr. Cooper then related' how, when , two islands at Martinique blew up, a British man-o’-war, fleeing from the vicinity of the disturbance, shuddered on several occasions as If It had struck a rock. Actually the boat had not; the shocks had been caused by : “ water hammer.” The bottom of the ■ sea had suddenly heaved’, the effect being that the ship was jolted as if 1 struck by s. huge ramrod. When a ship, on which Mr. Cooper was an err- : gineer, hove in sight of the Island a j days later, they saw a column of waterrise from the surface, quiver a few moments, and’ then subside; this undoubtedly had' also been caused by the “ water hammer.”' Morrinsvirie’s experience of' the past ten days: had been caused' by the same effect. Mr. Cooper said it was improbable that Morrinsville would get many I more severe shakes, although slight ones might occur for a short period. If his theory were correct, the fallen earth would be rapid2y consolidating and making the opening it had closed absolutely watertight. This might take a little time, and as each lot of water percolated into the terrific heat ; there would be a slight jolt.

MAKING; ENQUIRIES, GEOLOGIST IN MORRINSVILLE. Mr. .L. I. Grange, of the Geological Survey Department, Rotorua, is at present, in Morrinsville investigating the cause of earthquakes.