The ground east of the uplifted area sank, and parts of the Napier and Wairoa flats are over a foot lower than before the earthquake. In , movement along a north-trending fault seven miles west of Murchison raised the ground east of the fault by about 15 ft. The uplift gradually decreases eastward and dies out sixteen miles from the fault, facts indicating a slight tilt of the earth-block toward the east. Subsequent levellings showed that the block was sinking somewhat irregularly, a movement, no doubt, which caused some of the innumerable local after-shocks felt in the area over many months after the main shock.
A comparison between the records of destructive earthquakes in New Zealand and those in other seismic countries shows that the seismicity of New Zealand, on the whole, is surprisingly high.
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However, this is due to the occurrence of a large number of earthquakes of the semi-destructive type R. During the period sixty-nine destructive earthquakes are known to have occurred in New Zealand, forty-nine of which were of the semi-destructive type not exceeding intensity R. Of the remainder, fourteen were of intensity 9, and six of intensity The total number of earthquakes of all intensities, and the maximum intensity, reported felt in New Zealand in each of the years to were as follows:—.
Geological Survey; Annual Report for the year , p. Wellington, Dominion Observatory Bulletin The abnormally large number of earthquakes reported in the year was due to the swarm of local shocks in the Taupo region in the latter half of that year. Abnormally large numbers of shocks also occurred in , due to aftershocks of the Buller earthquake of 17th June, New Zealand earthquake statistics over the past hundred years or so show that certain parts of the country are subject to almost continuous seismic activity with occasional destructive shocks, while other parts are more or less free from seismic disturbances.
By combining early earthquake records with the more precise data of recent years it is possible to divide the country roughly into four seismic regions.
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These regions are classified below, in order of seismicity:—. All areas of the North Island east and south of an approximate line from the vicinity of Whakatane in the Bay of Plenty to the vicinity of Hawera in South Taranaki, and all areas of the South Island north of an approximate line from the vicinity of Hokitika on the west coast, through the region of Lake Coleridge, to Banks Peninsula:. Areas of the South Island, south of the boundary of region I:. The following table shows the average frequency of earthquakes in each of the four regions defined above:—.
It will be seen from the above table that region I, on the average, has nearly In region II, there is an average of 23 shocks per year, with about one minor destructive shock per decade. The activity in this region tends to increase gradually towards the east and south, where it merges into region I. In region III no major destructive shocks and only one semi-destructive shock have been recorded definitely. This occurred in the Mount Cook region.
However, early history suggests that heavy shocks occurred in the West Coast Sounds region in the years , , On the other hand, the eastern side is less seismic than the western. Region IV has very low seismicity. An average of one shock per year is experienced, and no destructive shocks have been known to occur.
In connection with the above facts, it must be emphasized that the boundaries between the seismic regions are not well defined, since one region generally merges more or less imperceptibly into another. Also, that seismic frequency is not uniform. This leads to the number of shocks being considerably above the average in some years and below it in others. The normal irregularity is increased by the occasional occurrence of earthquake swarms in certain regions.
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Probably the most notable swarm in New Zealand was that which occurred in the Taupo region in the latter half of The number of minor local shocks in this swarm was so great that only the stronger ones, or those affecting the adjacent region, were used in determining the average frequency of region I. The inclusion of all shocks would unduly raise the average frequency of this region as a whole.
During the period the number of deaths recorded in New Zealand as due directly or indirectly to earthquakes was Of these, were due to the Hawke's Bay earthquake of 3rd February, A table giving details of the number of deaths due to earthquakes in New Zealand was published in the issue of the Year-Book. Earthquakes in New Zealand are recorded by means of seismographs, and also by a system of non-instrumental reports.
The main seismograph stations are located at the Dominion Observatory, Wellington, and the Magnetic Observatory, Christchurch. The Dominion Observatory acts as a central station for ten other subsidiary stations in New Zealand and one at the Chatham Islands. The subsidiary stations are operated by officers of other Government Departments, by engineers of some of the Electric-power Boards, and by private individuals. The non-instrumental reporting-stations are located chiefly at post-offices and lighthouses. The following article on the climate of New Zealand was supplied by Dr.
Barnett, M. Stations at Ohakea, Woodbourne, and Wigram. Regular weather forecasts based on observations at 9 a. Under the present censorship regulations the transmission by the Broadcasting Services of weather reports and forecasts has been suspended, but district forecasts are still supplied to the press and to certain post-offices.
The New Zealand Gazette includes each month a meteorological section which contains a detailed climatological table for Kelburn, general notes on the weather for the previous month throughout New Zealand, and a table summarizing climatological data from over sixty stations.
Fuller tables of a similar nature are published annually by the Meteorological Office. Hitherto rainfall data from a further five hundred stations accompanied the other meteorological information in the New Zealand Gazette , but are now to appear in a separate annual publication. New Zealand lies wholly within the Temperate Zone, and it is also wholly and at all seasons within the zone of prevailing westerly winds though they are stronger and more persistent farther southward.
Owing to the isolation of the country and its narrowness in the direction of the prevailing winds, its climate is predominantly marine in character.
Nevertheless, the modifications due to the height and continuity of the main ranges and the general high relief of the country are quite considerable, especially in the South Island. There is, for example, a very great variation in the rainfall from the western to the eastern side of the Southern Alps, and for so narrow a country, features of a continental type are rather strongly developed in the interior of the South Island. By breaking up the prevailing winds and causing the air at different levels to mix, mountains tend, also, to prevent the stratification of the air into layers of different density.
Consequently very extensive and persistent cloud-sheets are seldom experienced. New Zealand therefore enjoys a high percentage of sunshine, a factor of great importance in the climate of a country with a high rainfall. The principal current in the surrounding ocean waters is from south-west to north-east. Off the west coast of the South Island, however, the current divides, one branch turning southwards to Foveaux Strait, while others pass through Cook Strait and round the northern extremity of the Dominion. The rather small range in climate from north to south is probably accounted for by this current.
According to the widely accepted classification of climates developed by W. Under the same formula are classified southern Victoria and Tasmania and parts of southern Chile in the Southern Hemisphere, much of Europe, Japan and Korea, and a strip of the west coast of North America in the Northern Hemisphere.
Generally, however, it is a climate characteristic of the ocean rather than the land areas of the Temperate Zone. Tables 1 to 3 appearing in the following pages relate to varying, but usually lengthy, periods. In Table 4 the duration covered by the respective averages for that table is given.
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Of all the climatic elements, probably the one that exerts the greatest influence on our lives is rainfall. It causes us much personal discomfort, but the production of the food by which we live depends directly on the availability of moisture from this source. Maps showing the distribution of mean annual rainfall appeared in issues of the Year-Book prior to The controlling influence of topography on rainfall in New Zealand is very conspicuous.
Areas exposed to the westerly winds have heavier rains than those protected from them by mountain ranges. Next, the greater the altitude the greater in general is the precipitation. There must be a limit beyond which precipitation begins to decrease again with altitude, but this has not yet been determined in this country.
The indications are that precipitation is heaviest between 3, ft. The annual total varies from about 13 in. The distribution of the precipitation throughout the year is little less important than its total amount, the effect of rainfall in winter, for example, being very different from that in summer. There are three principal factors controlling the annual variation of rainfall in New Zealand.
The first of these is the proximity to the high-pressure bolt in the subtropics. In this belt the rainfall year is divided into a dry summer and a wet winter season.
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We will call this distribution type A. As the distance from the high-pressure belt increases, the contrast between summer and winter decreases, so that by the time southern New Zealand is reached the variation due to this factor is small. The next most important factor is the influence of the prevailing westerly winds.
These bring rains to the areas exposed to them, while areas which are protected from them by mountain ranges have little rain when the westerlies are blowing. The westerly winds are strongest in spring, the maximum flow being in October. There is a temporary drop in February, followed by a partial recovery in the autumn, but the flow is least in winter.
The third factor is the convection which takes place during periods of light winds, clear skies, and intense sunshine, especially when the preceding winds have brought cold air over the land from the south. After conditions of the type mentioned have endured for several days, the convection is likely to be so intense as to produce local showers. These are often heavy, sometimes accompanied by thunder, and occasionally of the nature of local cloud-bursts. Rainfall of this type is most common in the interior of continents. Being caused by solar radiation, it is most frequent when solar radiation is strongest—namely, in summer.
According to type B, therefore, we would have a relatively wet summer and a dry winter. Table 1. Average of period of years.