QUAKES IN AUSTRALIA.

Waikato Times, Volume 116, Issue 19430, 3 December 1934, Page 9

QUAKES IN AUSTRALIA.

POSITION OF COMMONWEALTH. ■ r IS IT AN ASEIS.MIG REGION, r SHOCKS RELATIVELY MINOR. The earthquakes which have been experienced in New South Wales recently will no doubt be causing more alarm than their actual strength'would justify, because the Commonwealth has been regarded as an aseismic or earlhquakcless region. Many years ago ’quakes were recorded in South Australia comparable with some, of New Zelaand's major experiences, but Australia ba*s been considered to lie off [lie zones which have been most active during the last few decades. So far as is indicated by the records of tlie Magnetic Observatory ■al Ghrisl.eimrc.li, there is nothing actually identifiable will! the Australian •quakes. Eight shocks were recorded by one seismograph during Hie 2i hours ended at b a.m.. hut only one could lie classed as more Ulan a minor disl urbanci'. says I lie Sun. i Neither !lie lime nor the distance of I this parliriilar shock lilted in with the 1 cabled information of the Australian ■ shucks, II was I y pica I of a dislurb•l mice having ll< origin at an abnormal 11 (• 111 )t, mol. judging from the distance, ' it was probably au aftershock from

the Solomon Islands region, where seismic activity lias been fairly severe during recent years—much more so (ban has been 'the case in New Zealand. Of Shallow Origin. The fact that there were no definilo records .of the New ’ South Wales disturbances would create I lie impression that they were of a relatively minor nature, and probably of shallow origin. The ’quakes recorded in certain 1 parts of South Australia many years , ago were much stronger than the | present ones, but there has been no 1 activity of this nature there since. . The fact that Australia lias been regarded as an aesimic region is not so reassuring when the experiences ot . Ratlin Bay, in Hie north of Canada, are recalled. ' That territory, too, was regarded as aseismic until I>2 months ago. On November 20 of last year, though, ft was rocked by one of the mightiest ’quakes recorded in the past year, and aftershocks have been experienced in the same region, the latest being on August 21. The occurrence of a ’quake in such an unexpected place caused, some geologists lo put forward the theory that its origin was due lo a falling meteorite. Nowadays, however, it is possible by the co-operation of seismograph .stations io tell from Hie travel-limes of the waves of a shock the depth of ils focus/ If that shock had been , caused by a meteor, the records would j have indicated that the waves came • from the earth’s surface, whereas

what actually was shown was. that the focus was approximately'3o kilometers below the 'surface of tb<* earth. Australia’s Position. The experience of the Baffin Ba? region, therefore, indicates that Australia's privileged position as being classed with it, until recently,-as an aseismic region, might he equally insecure. " However, the 'shallowness of Die New South Wales ’quakes, as recorded, are reassuring in this respect. ' The officials at ' the observatory would not be drawn into a discussion on the relative positions of New Zealand and Australia so far as seismic activity was concerned beyong saying that Australia had been regarded as an aseismic region, while New Zealand had had sufficient proof that it lies within, an active zone, and that the nature of these shocks was not sufficient ground to shake Australia’s confidence in this respect. So far as New Zealand is concerned, 'though, its position can be dangerous only if adequate precautions against earthquakes are not taken.