EARTHQUAKES in CANTERBURY

Press, Volume LXXXIV, Issue 25553, 22 July 1948, Page 3

EARTHQUAKES in CANTERBURY

OPINIONS ON FAULT LINES REPORT of professor COTTON From Our Own Reporter WELLINGTON, July 21. Most of the earthquakes that have . ' n felt in Canterbury have been proved by eartn movements on a tault line in the Waiau district. This is the Son of Proiessor C A. Cotton, of Victoria University College, who has lade an extensive survey of the district and has presented nis report to Jhe New Zealand Council of Scientific and industrial Research. One of the most severe eartnquakes in the South island for a long time occurred in the Waiau area a few weeks ago. ••■Tne form of the Hanmer basin is a result of movements that still continue on an east-west fault along its southern boundary,” says Professor Cotton. “This is best called the Hope fault, for it determines the middle and lower course of the Hope river, as well as that of the Hanmer and a reach of the Waiau, and has been active recently in the valley of the Hope. The floor of the basin has been carried down by a depression movement that seems to be still going on. though no doubt intermittently. This downward movement has been in progress, so it appears, while the Leslie Hills block south of the Hope fault has been rising. “The fault, which here separates the moving areas, has been active recently. Earth movements on this line have been responsible for producing the majority of earthquakes in Canterbury, including probably the severe earthquake at Arthur’s Pass in 1929.” Kaikoura Fault Professor Cotton observes that in 1892 Mr A. McKay, referring to the earthquakes of 1888 in the Amuri and Marlborough districts, regarded the Hope fault as the continuation of another. also recently rejuvenated, which has since been called the Kaikoura fault, as it is along the base of the Seaward range. “The Hope fault itself is undoubtedly a major dislocation, whether or not it is one and the same with the Kaikoura fault, but only at the Hanmer basin is there clear evidence that a large differential displacement with a downthrow to the north has been in progress very recently on this line,” says Professor Cotton. “If. as seems possible, the Hope fault is not collinear with the Kaikoura fault, but intersects it, is intersected by it, or meets it at an angle, the Hanmer basin may perhaps be regarded as continuous with a still larger complex depression further north, which contains the valleys of the upper Clarence and Awatere rivers. “On the other hand, a hypothesis that reversal of the direction of the downthrow takes place at some time during the histories of some great faults may bring into line with topographical facts the theory that the Hope and Kaikoura faults are one. An explanation can be offered that ancient faulting has gone into reverse in a new faulting that has just begun/*