The Wairarapa Earthquakes of 1942

The second of a pair of 7th magnitude earthquakes struck the Wairarapa district just after midnight on the 2nd of August 1942.

The two quakes, which struck 5 weeks apart, caused extensive local damage but stunned officials by causing serious damage many kilometres away in Wellington. The experience was to have wide-reaching ramifications for local and national government policy.

The pair of Wairarapa earthquakes were the last of nine viciously large earthquakes that struck New Zealand in the 14 years from 1929. Both were located near Masterton, and struck in the middle of the night while New Zealand was focused on its war efforts as part of World War II.

A magnitude 5.2 foreshock struck near Masterton at 8:14 p.m. on the 24th of June 1942. A few hours later, the main magnitude 7.2 earthquake hit the area at 11:16 p.m. Both were shallow, at depths of about 12 kilometres in the overlying Australian Plate. The main shock caused serious damage in Masterton and nearby towns with some buildings partially collapsing and many others sustaining serious damage to masonry. The earthquake was felt as far north as Auckland and as far south as Dunedin.

In Wellington, over 100 km away, several buildings on soft soil suffered serious damage and many chimneys were toppled. Soil liquefaction was observed near Aotea Quay.

A normal aftershock sequence then followed, with the strength of the earthquakes diminishing with time. Repair work commenced, but at a slower rate owing to the absence of many tradesmen in the armed services overseas or in training camps.

About 5 weeks later, a magnitude 5.6 earthquake struck nearby at 4:47 p.m. on the 1st of August 1942. This quake was about 12 km deep, and there are differing views as to whether it was a foreshock of the larger event which was to occur just after midnight.

At 12:34 a.m. on the 2nd of August 1942 a magnitude 7.0 earthquake struck in the same area. This quake was deeper, being located in the subducting Pacific Plate at a depth of about 40 km.

The combined effect of two strong earthquakes in short succession caused considerable damage. The second event occurred before most of the damage resulting from the first quake could be addressed, and structures which had been weakened suffered extensive damage.

It was estimated that 20,000 chimneys were damaged by both earthquakes, and the Wellington City Council organised repairs to household chimneys in its area.

Building codes had been revised after the Hawke’s Bay quake of 1931, but this pair of quakes showed that local government had to take a more active role in managing local emergencies. The immediate outcome was that the Wellington City Council, at a time of war, undertook tighter control of the repairs to domestic chimneys.

A much larger change was the creation, about two years later, of the Earthquake and War Damage Commission (now known as EQC) to provide a pool of funds to allow individuals and businesses to recover from a natural disaster. The application of the fund has changed with time, and cover is no longer available for war damage. However, householders can still obtain some coverage for some natural disasters by paying a levy when they take out insurance cover for their houses.

In Masterton and nearby towns, the damage from the earthquakes was so severe that it took more than two years to clear up the rubble and completely rebuild. Resources were scarce, and the war effort was a higher priority.

The Masterton Library website has a background story on the 1942 and other Wairarapa earthquakes, with four photographs illustrating the damage that occurred in 1942.

[Earthquake data was sourced from the databases of the GeoNet project and its sponsors EQC, GNS Science and FRST.]

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