Hawke’s Bay Earthquakes 1931

A pair of magnitude 7 earthquakes shook Hawke’s Bay during February 1931. The first was a magnitude 7.8 quake that struck on Tuesday 3rd February near the shoreline 8 to 24 kilometres north of Napier.

Writing in The New Zealand Journal of Science and Technology, July 1933, F.R. Callaghan of the DSIR described the earthquake as follows: “The consensus of opinion is that there were two shocks of very different characteristics, occurring within a brief interval of some thirty seconds of one another. The first shock developed rapidly in intensity, had a distinctly uplifting motion associated with violent and confused swaying. Then followed a pause of about half a minute, till the second shock occurred, with a motion resembling a sharp bump downwards.” Callaghan quoted the radio operator of the m.v. “Taranaki” as stating “… the tremors continued for two and a half minutes from the time of the first noticeable shock.”

The earthquake was felt throughout New Zealand with the exception of Northland and Otago. In Hawke’s Bay, the main earthquake was followed by a brief period of quiet, but before long tremors commenced and continued for some days. Official records recorded 151 aftershocks that day, with 55 on the 4th, 50 on the 5th, 29 on the 6th and 24 on the 7th. The number of aftershocks then eased to less than 20 per day.

However, the rapid decline of the aftershocks was not to last. At about 1.30 p.m. on Friday 13th February another huge earthquake shook the Hawke’s Bay area. This event was officially set at magnitude 7.3 and centred about 50 km east of the earthquake of the 3rd.

In his book “Quake Hawke’s Bay 1931” Matthew Wright reports that this second event was New Zealand’s fourth strongest recorded earthquake. He writes, “Power failed three seconds before it was felt in Napier. People from Napier to Dannevirke ran for their lives as damaged buildings cracked and fell.”

He adds, “Some inland parts of Hawke’s Bay felt this aftershock more strongly than the 3 February quake. In Taupo, goods were thrown from shop shelves, but ‘there was no damage of any moment’. People rushed into the streets in Dannevirke and Masterton. In Wellington all but one of the clocks stopped in the Dominion Observatory, and ceiling lights in the Evening Post offices swayed ‘more vigorously’ than they had the week before.”

The earthquake of February 13th 1931 is widely regarded as an aftershock of the larger event ten days earlier. But Messrs Adams, Barnett and Hayes commenting on the rapid decline in the frequency of aftershocks in the Journal of Science & Technology stated, “The fresh outbreak on the 13th February, due to the severe shock on that date, may almost be regarded as a separate disturbance, although it probably arose from conditions produced by the original shock on the 3rd.” Earthquake counts shot up to 81 on the 13th, before dropping to 23 on the 14th, 18 on the 15th, 19 on the 16th and then slowly dropping away.

In all, 597 earthquakes were recorded at Hastings during February 1931.

The next event of note was to occur further north on February 17th.

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