MARLBOROUGH'S FAULTS

Evening Post, Volume CXVI, Issue 36, 11 August 1933, Page 8

MARLBOROUGH'S FAULTS

IN A GEOLOGICAL SENSE

EARTHQUAKE PROBLEMS

Two papers on seiamological problems wcro read at a recent meeting of tho Philosophical Institute ,of Canterbury in Christchurch. .' '.',/... "My paper deals with that part of Northern .Marlborough which, adjoins Cloudy Bay," said Mr. G. Jobberns, who discussed the physiography of Northern Marlborough. That. part of tho country consists of four quite separate blocks of the earth's crust. Theso blocks are bounded by earth fractures or faults on a large scale, and it is commonly believed that movement occurred on two of these fault lines.in the great earthquakes of 1848 and 1855." ■'"■ . ■ ' The first of these earth blocks/the .Limestone Range block, extended from Capo Campbell to the mouth of the Maxbourrie River.""This' piece of tho country mightjbe regarded-as an independent carth1 block—a' block .which had been able to. move upwards or downwards by itself quite\ independently of the rest of the 'country: ■ i'\' Tho second of these earth blocks was the piece of country containing tho lower'; yalloy. 'of: * the;: Awatere^ River near Seddoh,' the' valley of 'the Blind Eiver, and- the area round Lake Grass--mere. It was a different kilid of country altogether from, the rcsir of Marlborough, consisting of soft, grey, sandy . mudstone, or papa, i This" area was bounded on • the south by a big fault, and on, the north by another fault which ran.along the baso of the Vernon Hills" arid which was one of.i the most important-faults in the South Island. Movement along.it was supposed to have taken place in 1848, | causing the great earthquake of that | year. The records of this: earthquake were not very clear, but a great crack was supposed to have been yisible running up the : Awatere ' Valley nearly sixty miles. ; i; ■ v' ! i - Tho third earth block was that of the Vernon Hills, a remarkable range of flat-topped hills ending1 at ■, the coast in magnificent cliffs nearly 1000 feet high. The-section of tho cliffs showed the hills to be made" entirely of gravel. These.grave!beds had been lifted bodily up to their present position, showing thai-the range had: behaved as, an independently moving block of the earth's crust. . '>■■■-.. The fourth crust block was- the floor of the Wairau Plain. This, piece of the earth's crust had subsided: between two converging faults to form a • tug triangular depression formerly occupied by the. sea.-, Tho filling up of this depression ■ had formed' the flat, low-lying Wairau Plain—the .■; plain naturally reclaimed from the' sea. "The special physiographical interest of this part of Marlborough," said Mr. Jobberns, ■''is that* it affords au example of an area of country made up of a .iumble of fault-bounded earth blocks. Forces of compression caused'a warping or arching up of the crust and the crusti broke ,into blocks. ' Tha breaks represent fault lines by which the blocks are bounded. When the crust is further compressed any one of these ' earth blocks is capable of moving independently along a fault plane, and if sudden movement of this kind ,■ occurs au earthquake must vesult. Tho cause: of■••:' the earthquake would be merely the terrific jolt given when a piece of the country uioved suddenly upwards or downwards independently of the Test of tho countiy." Professor B. Speight read again the papor given by him' some time ago entitled "Deductions from the Arthur's Pass Eathquake." Members discussed tho paper and expressed-approval of Professor Speight's proposals for minimising the risk of damage from oarthquake. The opinion was also .expressed by Professor J. E.;L. Cull and others that it was vital that the Government and public bodies should go thoroughly into the question and that tho Society should strongly support tho Building' Construction Bill which was to como before the House next session.