SHAKEN COUNTRY

Evening Post, Volume CXI, Issue 71, 25 March 1931, Page 10

SHAKEN COUNTRY

GEOLOGICAL SURVEY

AN AUCKLAND REPORT

Support of the conclusions of the Government geological survey party is given in the report of the members of the Auckland University College science expedition, which recently visited the earthquake areas.

"The cause of the fracture seems to have been tlio accumulation of a comprcssivo strain exerted more or less horizontally along a north-west-south-east line,''' states Professor Bartrum, professor of geology (according to the "Herald"). "This caused the outer rigid layers oC Hie earth to develop a north-east-south-west shear-fracture, along which the north-western earth-masses were pushed eastward over the south-east-ern. This is indicated at the surface by a pressure-mound raised to a maximum height of perhaps 4ft in one locality I visited, north-east and. southwest for several miles near Poukawa, several miles south-west from Hastings. The up-arching of the coastal and shore region near Napier, illustrated by the creation of now land from the floor of the inner harbour near "Westmcre is due to the same process, and the conclusion of the officers of the New Zealand Geological Survey that the main seat of origin of the earthquake is approximately along the line of fracture in Poukawa Valley and its northern continuation appears to be thoroughly justified. "After making all duo allowance for differences in the rocks and their attitudes, the slips and general disturbance oC the hill slopes were of far less importance than I had expected in view <>f what I had seen resulting from the Murchison earthquake. It was most surprising, in view of the high intensity of the shocks, as demonstrated by their destruction of buildings, that larger and more numerous slips did not come from the steeper hillsides. This undoubtedly is to be accounted for by the providential relative dryness of the rocks following a. period of low rainfall."

Beferring to the flood danger in winter Professor Bartrum says: "If what X saw on the route from Taupo is typical of conditions elsewhere, I do not think that the dangers to be apprehended from such floods are likely to be so great as on the West Coast area affected by the recent Murchison earthquake, for the slips seldom appear likely to carry rocks and timber sufficient iv size and quantity to form important valley barriers." The report continues: "The most striking surface effects of the earthquake appear wherever the surface material is relatively poorly consolidated, as in alluvial plains and infilled arms of the sea, such as are exemplified by much of the lowland fringe of Napier city. Embankments have been caused to spread laterally with the production of fissures more or less parallel to their sides, and railway tracks, •especially where situated on curved embankments, have been distorted in most interesting fashion. "Where streams have been flowing through unconsolidated areas their banks have sometimes boon squeezed together, in several instances forcing the bridges crossing them noticeably higher.

"Muck of Napier lias been built on land, that is imperfectly consolidated, so that the damage to sewage drains and water and gas mains and pipes must undoubtedly be most extensive, quite apart from complications to the problem of drainage arising out of unequal coastal uplift. For some reason or another telegraph and power poles have not been so extensively displaced as by tli© Mur-chison earthquake. As in tlie case of this latter earthquake, also, there appear to be grounds for the belief that the ends of spurs have been shaken with especial severity; it is possible that for this reason the seminary at Green Meadows, where a modern forro-concrete structure was destroyed, was more vigorously shaken than buildings in other locations, but there is no extraneous evidence clearly in support of this suggestion."

In conclusion, Professor Bartrum said that, apart from the object-lessons given by the catastrophe with respect to the proper construction and topographic location of buildings, it was obvious that too little was being done in New Zealand to further the scientific study of earthquakes. There was every reason for belief that more or less precise prediction of impending earthquakes . would be attained if proper scientific study of their portents was made.