SEVERITY OF EARTHQUAKE

Taranaki Daily News, 6 September 1929, Page 12

SEVERITY OF EARTHQUAKE

TITANIC HEAVE FROM BELOW LAND PUSHED UP SEVERAL FEET. OPERATION OF COLOSSAL FORCES. The severity of an earthquake is generally' gauged by the public according to the amount of damage done to buildinws and to the loss of life incurred. ' Adopting these criteria, the Murchison earthquake of June last was bad enough, but the latest data available on the subject show that this earthquake involved the operation of colossal forces. An area of land nearly IS miles in length, perhaps 50 miles broad, and probably of considerable depth, was thrust up by titanic forces from below, and has stayed up. The elevation was not of the same extent throughout, for the result is as if this huge, block of land has been tilted up from one end, the maximum elevation being over 16 feet.- .

When the- devastated area around Murchison was. inspected immediately after the earthquake, it was suspected that there had been an uplift of the land,, but to what extent was not ascertainable until the Public Works Department carefully took levels throughout the area and compared them with the previous levels. Then it was discovered what a gigantic upheaval there had been, one which fairly staggers the imagination. The work of taking the levels again was started right back at Glenhope, so as to be sure of starting on ground which had not been altered in its altitude, and the party taking the levels worked down from there through the Buller George. For the first ten or fifteen miles no alteration in previous levels was discovered, but by the time Oven Junction was reached a progiessive deviation from previous levels was noticeable. In six miles thcre z was found to bo a rise of two feet. A slight drop followed, but in the vicinity of Murchison the grade of the incline of the uplifted block of land became. steeper and fore pronounced. At a point just past the mouth of Doughboy Creek there was a rise of 10ft. Gin. In the next half-mile there was a drop of Oft. The height of the uplift had increased to 13ft. 3in. by the time O’Sullivan’s Bridge was reached, but opposite the Maruia Valley there was another marked drop. From thence onward, however, for the next mile there was a progressive rise until the maximum of over 16ft. was reached. During the next one and a half miles there is a fall to 13ft. 9in., followed by an abrupt rise to a foot higher. At White’s Creek, where the fault lies, the end of the uplift was reached and the ground level falls back to normal. j The general effect, therefore, has been that one or mbre geological blocks of land took up the movement engendered down below' and were tilted, and perhaps rotated slightly as well. The inclined plane thus formed is towards t’e cast, the western boundary (the White Creek fault) showing the maximum elevation. DAMAGE IN THE VALLEYS. It will be observed that the tilt, although progressive from east to west, is not uniformly continuous. There are breaks every now and again, and these correspond to places where the valleys run into the Buller Gorge. What very likely happened was that the whole block of land was titlted up from below, but buckling occurred in valleys down which rivers flow and along which are often minor geological faults. This buckling in the region of the valleys would account for the major effects of the earthquake in those parts, coupled with the fact that the valleys would be composed of alluvial soil which would be more shaken than the solid rock. NEW ZEALAND GOING UP. The measurements made prove conclusively that the effect of the earthquake was an upthrow towards the east and not a downthrow towards the west. This movement is in accordance with the usual direction of earth movements in New Zealand. New Zealand is rising generally and also by sections, but as the general rise is about proportional to the rate of denudation, the country as a whole retains approximately the same height above sea level. Evidence of the general uplift of the country can be found in raised beaches all round the coast. Geologically speaking, many of these raised beaches are of recent date; historically speaking, the raised beaches, around Wellington are very recent and date back to the 1855 earthquake. The 1855 earthquake elevated a fair area of land, but the maximum elevation did not exceed nine feet. The Murchison earthquake, therefore, with its nearly double elevation, must have been a much more formidable affair. Had it occurred in the neighbourhood of Wellington, apart from disastrous results to lives and property, the effect would have been to convert Wellington’s noble"’harbour, if not into a land-locked lake, into a harbour in which would be imprisoned most of the shipping which happened to be in it at tl.s time. Had the Buller River been a more sluggish stream, one effect of the uplift of the country through which it flows might have been an alteration in the direction of its flow, but the Buller is u rapid enough stream to make light of an obstacle such as a 16^-foot uplift. FURTHER INVESTIGATION. The full extent of the area of the country uplifted has not as yet been ascertained, neither is it know for certain how many geological faults are involved. Probably it will- be found that several distinct geological blocks have moved, but much of the. country is difficult to traverse for the purpose of making investigations. Now, however, that finer weather can bo expected, officers of the Geological Survey Department will be able to explore further afield. Possibly other uplifts may ~u discovered- in some of the remoter regions. Comparatively minor elevations and depressions have already been noted in places, Karamea, for instance, having apparently been depressed to the extent of a couple of feet. It will probably bo some months before all the possible data about the earthquake will be collected and correlated. But in the meantime enough has been discovered to show that the Murchison earthquake can be classed as a real “world-shaker.”