EARTHQUAKES

Hokitika Guardian, 24 July 1931, Page 5

EARTHQUAKES

SCIENTIST’S ADDRESS.

ACCURACY UP PROPHECIES. «;

WELLINGTON; July 22.

Much interest has been taken in an "earthquake” series of lectures arranged by the Wellington PhilosophicalSociety and the Dominion Museum’ 1 lecture room was full to overflowing when Processor C. A. Cotton gave the third lecture of the series, one on. "Earth Movements and the Causes of Earthquakes.” . Reversing the order-of the title, Professor" Cotton first touched upon the cause of earthquake, .The old hypothesis, lie said, connected earthquakes with volcanic activity., r . There was sometimes something in this view, but the connection between the two was now generally considered to be only indirect. The theory that earthquakes were caused by the ’’collapse of subterranean caverns could be put aside. There was another theory that earthquakes were caused by the slipping of soft sediment on the steep slopes of , the ocean floor, but this was a confusion of thought as regards cause and effect. West of Cook Strait was an r earthquake centre which gave Wellington its little shakes ; but in'this region there was no steep slope and no sliding Most big earthquakes were due to the slipping of a fault, although this did not exclude the possibility of the arching or folding cf strata as well The Murchison earthquake was due to a vertical fault movement, and possibly that of Napier also.'. Most big earthquakes could. be traced . to vertical ' rather than horizontal fault movement, but the San Francisco earthquake of 1906' was caused by a horizontal movement along a fault. The effect had been traced for 200 miles . along a line parallel to the coast of California. Professor Cotton here ' showed lantern slides showing the effects of this horizontal, movement. One slide showed the front drive of a house > which before the earthquake, finished opposite the front door, as .most' drives do. But ;dfter the earthquake it was many feet to one side. "This is the only joke of the lecture,”, remarked Professor Cotton, “but ; it could have been no joke for the people concern- • ed.” Other ;slides- showed; similar "ef- . fects upon fences in New Zealand, resulting from- the Napier 'earthquake and from previous earthquakes.' Cotton,.; .briefly 1 discussed what is known as , the elastic-rebound . theory of. earthquakes, tickled the imagination. ofitlie audienceby his description of migrating mountain masses. Earthquakes, he , ‘said : could be prophesised on the elastic-re-°ht)UTTd “theory; : in .ftrct“iHlvas .tfiS'b'Bly way in which they could possibly beforecast, but the prophets would no! be 'able to be more accurate than with In ten to twenty years. 'Hie best that they could say would -be that an j earthquake would take place some day in a particular locality.. , ‘ A