Wairoa Earthquake Swarm, March 1976

Thirty years ago, the residents of Hawkes Bay, Wairoa and Gisborne were greatly alarmed by the swarm of shallow earthquakes that plagued the area in late March of 1976.

The swarm, centred about 30 km south of Wairoa, included four 5th magnitude earthquakes which caused considerable damage in the township.

The earthquakes started on the morning of March 17th, 1976 but weren’t reported by residents until a magnitude 4 earthquake occurred at 20 past six on the morning of the 19th. All was again quiet until Sunday 21st.

At 5:59 a.m. a magnitude 5.4 earthquake heralded the real action for Wairoa. There were slight tremors for the next six minutes at which point another sharp jolt of magnitude 5.4 struck at 6:05 a.m. Things fell quiet for a few minutes until the tremors started again at nine minutes past six. A series of magnitude 4 quakes struck at ten, eleven and seventeen minutes past six, and a further two, 11 seconds apart at twenty past.

The earthquakes then eased in strength until a magnitude 5.3 quake struck at 6:38 a.m. Residents of the town reported feeling the ground vibrate with a grinding motion followed by a sickening swaying.

As a result of all this activity, several buildings in Wairoa suffered structural damage, dozens of chimneys were cracked and some toppled, most shop owners lost stock when contents were thrown from shelves, and burglar alarms rang. Major water damage occurred at Wairoa Hospital when some of the sprinklers were activated, and many shop windows were shattered.

The swarm of quakes continued through Sunday, while townsfolk cleaned up. Some forty smaller earthquakes were recorded until Sunday evening when all became quiet. Half of these were reported as being felt, some as sharp jolts.

The next morning, Monday March 22nd, Wairoa residents were again chased from their beds at 5:50 a.m. by a magnitude 5.2 earthquake. By this time, they must have been wondering where things were leading.

However, activity then eased, with another 8 earthquakes (all but one under magnitude 4) over the next few days. Four of these quakes were reported as felt.

In Gisborne, many of us leapt dutifully from our beds to shelter under doorways when the first earthquake struck at about 6 o’clock on the Sunday morning – the damaging earthquake of March 1966 was still fresh in our minds! Thinking “that was that” we hopped back into bed hoping for that Sunday sleep-in. A few minutes later some of us were up again as the next of the larger quakes rattled the house.

A “doorway conference” was held, and we all elected to return to bed to see where this was going to go. As the smaller earthquakes occurred, we shouted back and forth within the house commenting about the gurgling noise that accompanied the earthquakes that made the house sway. At the time we lived in a brick house on a solid ring foundation, but part of the section had been a bit boggy when we moved in as it carried water from further up the hill. We had dug a herring-bone network of tiny “canals” and installed field drains to make that part of the property useable in most weathers, and it had become a veritable jungle of vegetables with the assistance of my green-fingered father. However, the gurgling from the ground that accompanied the swaying induced by the continuing earthquakes was a little alarming.

When the third of the 5th magnitude quakes did its thing at about twenty to seven, we gave up on the idea of a sleep-in and decided to get up for a hearty breakfast while we waited for the hourly news broadcast on 2ZG or 2YA. By that time, things had eased in Gisborne, but Wairoa was still suffering the shakes.

I understand that some minor damage was reported from places in Hawke’s Bay, but on this occasion, it was Wairoa that experienced the “substantial damage.”

[sources: Seismic data from Geonet and its contributing agencies. “The Evening Post“, Wellington, Monday March 22nd 1976. Family archives.]

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