EARTHQUAKE CAUSE

Press, Volume CII, Issue 30220, 27 August 1963, Page 24

EARTHQUAKE CAUSE

Fault Theory Challenged Records of deep earthquakes in the Rae uilhi-North Taranaki area indicate that the cause was more Likely to be a rearrangement in the structure of the material of the earth than a movement related to a geological fault, Dr. R. D. Adams, of the Seismological Observatory. Department of Scientific and Industrial Research, says in the “New Zealand Journal of Geology and Geophysics.” Three of the earthquakes occurred at depths near 230 kilometres, and three others near 600 kilometres. Two of the former group, and two of the latter, were “twin” shocks. The deeper “twins” occurred first, at a separation of four and a half minutes, on March 23, 1960. Their magnitudes were 61 and 6.2 respectively. The other pair took place at an interval of only 80 seconds on March 27. Their magnitudes were 6.6 and 6 plus. The very deep earthquakes gave shocks in which at most observatories the first movement was in the opposite direction to that from the moderately-deep earthquakes. “It is doubtful if sudden faulting can occur at depth,” says Dr. Adams. But even if this were - possible, twin earthquakes could not readily be explained as arising from shift along fault-lines. “Once initial friction was overcome. any movement that started on a particular fault would tend to continue until the stress in the surrounding rock was largely relieved. On the other hand, if earthquakes are caused by n physical rearrangement of tile structure in the immediate vicinity of the focus, there seems no reason why such changes could not occur in two adjoining volumes of rock within a short interval of time ”