EARTHQUAKE ZONES

Taranaki Daily News, 12 February 1931, Page 15

EARTHQUAKE ZONES

NEW ZEALAND “FAULTS.” . . . FRACTURES TRACED. Dr. C. E. Adams, Government Seismologist, describes in a recent article the earthquake “fault” systems of New Zealand. ■ In New Zealand (he says) many great faults and fault-zones have been traced for long distances, on geological topographical evidence, but of these a few only have been active since European occupation. A notable zone extends north-east through the centre of the North Island from Mount Ruapehu to White Island. South of Ruapehu it has not been .definitely traced on the surface, /although from the positions of the foci of the groups of earthquakes it probably extends past Wanganui, across Cook Strait, and along the south-east shore of Tasman Bay to the South Island. The volcanic phenomena of the Rotorua-Taupo region, together with the recent remarkable earthquakes at Taupo, indicate that earth-stresses are still accumulating along the great fracture-zone. Another important fault system extends through North Canterbury, Marlborough, East Wellington, and Hawke’s Bay. Its general course is north-east, parallel with the Taupo belt and the principal mountain ranges of New Zealand. The Marlborough valleys, as well as the lowlands of the Hutt and Wairarapa districts, are directly controlled by fractures of this great system. In addition to many less severe shocks, the Wellington earthquake of 1855 was due to displacement along one of the major fissures. The southern end of the known active portion of the great fracture-belt is crossed by several important east-and-west faults; and the Hanmer earthquake of 1888 was due to the reopening of a fault extending in this direction along the upper valley of the Waiau-ua River.

The edge of the submarine plateau of which New Zealand is the most elevated portion lies about 200 miles east of the North Island. Thence it extends north-eastward for hundreds of miles in a nearly straight line. The sea floor to the east is several thousand feet lower, and the precipitous edge of the plateau probably is the scarp of a great fracture-belt. The most active seismic region of New Zealand is at or near the southern end of this submarine scarp, and here have originated several severe earthquakes. Another submarine earthquake zone, presumably also a fracture-zone, extends parallel with and some fifty miles from the east coast of the South Island, from opposite Christchurch to southeast of Dunedin. Numerous unimportant earthquakes have originated from this zone. .

Another group of earthquake foci occurs off the west coast of the North Island, opposite Raglan and Kawhia. This, like the other seismic zones, extends in a north-easterly direction parallel with the main mountain axis of the Dominion. Few earthquakes have been recorded from this locality, the principal being in ISB2 and ISOL.