EARTHQUAKE EFFECTS

Hokitika Guardian, 7 September 1929, Page 8

EARTHQUAKE EFFECTS

MURCHISON DISTRICT. GEOLOGICAL SURVEY 13Y PROFESSOR SPEIGHT. . CHRISTCHURCH, September 5. For the purpose of making a special examination of the earthquake area,' Professor Speight and a party of geology students from Canterbury College left for the AYest Coast on August 16.' Professor Speight returned to' Christchurch yesterday, and he gives an interesting account of his survey. In his opinion, the area which was most affected was around Murchison, in the direction of Ivaraihea, hut as the northern and middle country was thickly covered with bush the party did not have the opportunity of visiting that part of the district in the time at their disposal. There was no aoubt said Professor -Speight that the main disturbance was associated with the AA T hite Creek fault, which also crossed the Buffer River. At the fault there was an uplift of 13ft 6in, and, according to reports, it diminished towards the east. At Murchison the uplift was oft, and at Glenhope 2ft, which meant that a big block of country had definitely tilted. There was no other evidence of a movement of the earth’s crust, but, according to the report of a prospector at Mokihinui, Mr Bean, the movement was prolonged in that direction. The prospector had noticed that the banks of the Mokihijiui River had been effected, one being higher than the other'. That was also noticeable on the Buffer River, where it was crossed by the fault. One of the banks was affected for about half a mile.

It seemed at first sight that the disturbance had been greater in the norc.iern districts than at Murchison, said Professor Speight, but that opinion was subject to further surveys in that district. One of the main geological effects was the great slips. They were especially noticeable where the beds had been weak, such as where there was limestone on papa beds, and on scarp slopes where the strata appeared on the surface. In some cases, such as along the Blackwater River, there wore slips for miles. “A strange thing is that the maximum amount of the disturbance was not alongside the fault,” said Professor Speight, ‘‘as a concrete bridge there was scarcely damaged, it having only one small crack. A few miles distant the disturbance was more intense. Some of the slips occurred at the time but others were subsequent. Owing to the shattered nature of the country a good deal of additional damage may be done when there is heavy rain. Some of the hill slopes are not stable and it may Ik; years before they are especially in those cases where the beds are weak. Granite country was little affected, and at Cape Fouhvind there was scarcely any damage. The places that suffered most were the flats and alluvial ground, and this probably explains the intensity of the shocks at Murchison, AYestport, and Karamea It is fairly certain that the sinking of areas of ground occurred. At the mouth of the Mokihinui.River an area of 100 acres has ' apparently settled down. A noteworthy occurrence.. was the amount of water that was forced up in the area, and the discharge of sand, which built up small mounds.”

The slips were likely to continue for several months, especially in those places where there were weak beds said Professor Speight. In some places farms had been practically obliterated while others had been materially reduced in value. However, the number of farms affected was not great. One of the greatest difficulties was communication, and in some cases farmers were unable to take their products to the market. Large gangs of men were engaged in clearing the slips and it should not be long before reasonable communication was restored. Referring to the question of sounds Professor Speight said that while it seemed to be the consenus of opinion that the sounds came from the sea yet many of those who had heal’d them would not express an opinion as to the direction. The sounds were sometimes sharp and at other times like peals of thunder, but they wore not always accompanied by earthquakes. The sounds were due to after-shocks . and varied in the different districts. They .were the adjustments o>f blocks of earth in the crust at a shallow depth. “Some of the sounds were heard before the earthquake, and one detonation was heard with tremors the same morning,” added Professor Speight “It appears that they may lie - taken as an indication of an approaching earthquake if they are heard continually for some time. They have been heard before in the distinct and they were put, down as petroleum or gas explosions. However, there is no pi oof that this is the case. The sudden uplift was part of a general disturbance that has been going on in past geological times.”