EARTH FRACTURES

Sun (Auckland), Volume III, Issue 726, 27 July 1929, Page 8

EARTH FRACTURES

WHERE NEW ZEALAND IS WEAK CAUSE OF ’QUAKES | {Written for THE SUN bp T. Walsh.) j Disturbance of the earth’s equilibI riurn, vast periods of time ago, resulted ! in the fracturing of an enormous land ! mass which moved apart; and into the gap poured waters from the Pacific Ocean. At some period in the stabilisI ing of the earth’s mass subsequently, Xew Zealand was wrenched off a land block to the west, possibly Australia, and with, literally, ups and downs since then it has held together, except for the earth movement that tore the land into two; to form the South Island and the Xorth; forming Cook Straits, very likely at the same time constituting Stewart Island. Those fractures of the earth’s crust which formed the two straits ran east and west. Tasmania resulted, in all probability, from the same major movement. At the present time the earth tremors in Xew Zealand are almost avright angles to those older movements, indicating that the forces now setting up strains in This region of the crust of the earth are the results of different stresses. It is believed the deepest fracture in Xew Zealand is off the east coast of the South Island, opposite Oarnaru, for it is calculated that earth tremors that shook Canterbury in 1888 (and were part of the movements that reopened the fracture on the ancient and wide fault at Tarawera, made visible in the Tarawera eruption) had their origin at a depth of 24-25 miles below the surface. OLD FAULT LINE As shown on the diagram, the lines of ascertained weaknesses in our land mass are parallel to the axis of the Southern Alps and their continuation (Rimutaka Ranges, etc.) in the Xorth Island. Until the recent violent shocks down the Duller Valley (an ancient fault line) the most disastrous earthquake in Xew Zealand was that recorded at Wellington in 1855, following a severe ’quake in 1848. Other severe 'quakes occurred, as shown on the map, of the south-east coast of the Xorth Island in 1863, 1868, 1890 and 1904; in the Xorth Taranaki Bight in ’1891; off Cape Farewell and Cape Stephen in 1773; at Cheviot in 1901 and 1922; off Oarnaru in 1870 and 1888, and off the Dunedin coast in 1872. The visible evidence of mountains and valleys in Xew Zealand show that in remote times the country was

vracked by earth movements, many >f them very deep seated and all due o the primal and earth-shaking twist hat made the Pacific and its islands, rhe deduced evidence from scientific ►bservations, of the ’quakes that have iccurred during European times, re-

veal that there is a series of fracture lines extending far into the bowels of the earth; that our islands are, geologically speaking, somewhat unstable; that movements almost anywhere along the gigantic Pacific fault that bisects the globe will cause some movement in the broken strata on which our land rests. This series of faults may be said to begin in the deep submerged valley that separates the Chathams from the South Island. The next more or less ascertainable line is off the east coast of the South Island, near Oarnaru and Dunedin, extending to Banks Peninsula. Its continuation may be traced off the south-east of the Xorth Island, about ISO miles at sea. A third line runs under Canterbury, through Cheviot and "Wellington, and under Hawke’s Bay; a very obvious weak point is near Sumner, whence come most of the shakes that trouble Christchurch. All these lines are east of the mountain backbone of our islands. On the west side of the backbone the series of faults continues. A tremendous crack is visible from the Bay of Plenty to Ruapehu. Seventeen volcanic craters, commencing with White Island, may be counted, and it is along this heat tortured fault that practically all the active thermal phenomena of Xew Zealand is to be seen. The crack dives down, but though not easily traced on the surface it apparently continues under "Wanganui and under the waters separating the islands and down past Xelson, even to the South Island lake country. It is by far the most serious crack in the supporting strata. If it ever happened that some ill-omened earth twist was to cause another rift in Xew Zealand, similar to that which tore the South and Xorth Islands apart, the line of the separation would be from the Bay of Plenty to the Bight about Wanganui. FIRST EARTHQUAKE

Between Wanganui and Stephen Is-> land, on the opposite side of Cook Strait is the centre of more earthquakes than is recorded from any other part of Xew Zealand. In this region Captain Furneaux noted an earthquake in 1773, the first that any European had recorded. Xo doubt the native traditions carry down stories of earth movements in this country, and if the Maori had been able to save the traditions of the people whom they found here, we should have some very interesting seismic history on record. The Maori was not ignorant of the fact that all the volcanic activity in the Pacific is inter-related, and has woven a series of legends about old Mata-alio, son of the Fire Goddess, and his expeditions to Aotearoa. Volcanic activity is not so much the cause of quakes as the result of movements of deep buried strata, which movements open vents for the release of part of the molten mass that composes the interior of our globe. Along the crack that extends from White Island to Wanganui and past Xelson, has occurred the recent devastation apparent at Westport, Murchison and Karamea. Just recently there was some .slip in the foundations of the hills at Otira that brought down hillsides there. Tt was evident that, more activity might be expected along

the line, had it been possible to view all the facts in their proper perspective. There is a focus for shocks near Xelson, regarded as a shallow one by experts; that is to say, about five to 19 miles below the surface. Xorth ward from Stephen Island the activity is deeper—about 15 miles, and is apparent over an area 10 miles wide. It is worth noting that some years ago there was a series of earth tremors in the lake country of Otago, the southernmost part of the great fracture, though it continues toward the southern ice-barrier. A mystery that surrounds the report from the lighthouse men at Cape Farewell is that they saw what seemed submarine volcanic activity at sea. It may possibly be explained by the supposition that there is another fracture line just west of the South Island, and that it extends northeasterly to the known fracture that exists off Kawhia, where there is a centre from which quakes radiate, and where there happened a number of shocks in 1891. SUBMARINE ACTION Two captains of ships that were crossing the Tasman about the time of the 'West Coast shakes reported disturbances at sea that would, in their characteristics, lead to the surmise that under-sea volcanic action had taken place. Following the quakes at Taupo in 1922, which seemed to travel inward from the Bay of Plenty and which resulted in a lowering of the land level about the lake, there came a period of mild tremors at Morrinsville, which is along an old fracture belt that runs parallel to the north-west axis of the northern portion of tho Xorth Island approximately from Rotorua to Xorth Cape. It is along this zone that former volcanic activity can be traced to Auckland and beyond. On it, too, there is still some faint thermal action as evidenced by the hot springs at Te Aroha, the Hauraki Plains, Waiwera, Helensville and Kamo. Our familiar old friend, Rang! - toto, was in all probability the last fierce outburst of a dying volcanic energy on this line in the far past. Since 1880, inspired by the tragic happenings at Tarawera, the Government has maintained over 80 observation stations throughout Xew Zealand, and recently installed three seismographs, with photographic recording gear, two of them at Wellington and one at Christchurch.