MR HOGBEN INTERVIEWED.

Otago Witness, Issue 2719, 25 April 1906, Page 30

MR HOGBEN INTERVIEWED.

Mr G. Hogben, M.A.. a recognised - authority on earthquakes, has an up-to-date \_ seismograph under his house in Tinakori road. At the time of writing he had not yet developed the record taken yesterday, but no doubt the San Francisco earthquake will be duly recorded on the photographic tape, works automatically. Strangely '■enough, the instrument recorded a severe earthquake in seme part of the world some ".ipime ago of which no mention was made the newspapers. Regarding earthquakes .generally, Mr Hogben said they were only (symptoms of movements that were going on below 'the earth's surface. If the movements went on gradually there would be no appreciable manifestation of the change on ithe surface, but if, on the other hand, the movements were rapid and irregular earfch- - quakes would occur. It was important to "f remember -, about earthquakes that their - origin- lay in general from five to 25 miles - -fbelow the earth's surface ; that the rocks in = ■which the origins were situated were very xigid and far more highly elastic than air, ox string, and that the effects observed in - Sharp or severe earthquakes (whether they -' were the disturbance of more or less mov- " "able objects' upon the earth's surface or ~jof "part of that surface itself) were really generally secondary effects. Two important causes of earthquakes were the gradual cooling of the earth and the loading of the ocean bed through denudation of the land surface. In explanation of the second cause he Baid^ the rivers of a sea, for instance, brought down enormous masses of^

material, ' which were deposited in the ocean beds, '^he land surface pressure "was accordingly reduced and the enormously increased pressure on the sea beds caused internal, movements which ultimately resulted in fractures, and caused what we call earthquakes. A line of weakness runs right through California, but San Francisco is not the worst city in the country so .far as earthquakes .are concerned. It lies in a seismic, but not in a volcanic district. The earthquakes in San Francisco, Mr Hogben thought, were due to readjustments of the earth's crust below the Rockies and parallel ranges, including the ranges in the ocean bed to the west. They belonged to the same system as those in Mexico. Mr Hogben does not believe that volcanoes and earthquakes are due to the same cause. They were quite distinct. Where a volcanic eruption took place there were, of course, earthquakes, but they were ' purely local. In the seismic region on which San Francisco is situated he said it was evident big adjustments were going on, and there would almost certainly be recurring shocks. Where there were big mountain ranges earthquakes would occur. In Japan and the Himalayas, for instance, disturbances were and would be frequent.