Quakes in NZ, morning of 7 Sept

Hawke’s Bay, scene of one of the most damaging earthquakes to have ever hit New Zealand, has today been rattled by an earthquake measuring 5.2 .

The 15km-deep quake was located about 20km southeast of Porangahau at 10.48am. It was felt in the Hawke’s Bay and as far away as Wellington. It followed a smaller  3.6 quake that happened 45 minutes earlier, centred 30km east of Waipawa. See Geonet report

According to a report on Yahoo.co.nz on 6 Sept the recent 7.1 quake in Christchurch could set off a chain of quakes elsewhere in New Zealand:

Canterbury’s magnitude 7.1 earthquake may turn out to be precursor to New Zealand being hammered by a series of big quakes. Victoria University geophysicist Euan Smith said there was a potential for big quakes to trigger other big quakes.

“The 7.1 magnitude quake that rocked Canterbury on Saturday morning came from a previously unknown fault, but if recent history is anything to go by, it could be one of a series of 7-plus magnitude quakes, some of which are still to come,” said Prof Smith.

Until last year, seismologists regarded the past 30 to 40 years as a quiet period in New Zealand as there had been no big on-land earthquakes.

Such large earthquakes, sometimes came in clusters lasting 10 to 20 years, which were then followed by a quiet period. Read the full report here

From Wikipedia:

The 1931 Hawke’s Bay earthquake, also known as the Napier earthquake, occurred in New Zealand at 10:47 am on Tuesday February 3, 1931, killing 256 and devastating the Hawke’s Bay region. Centred 15 km north of Napier, it lasted for two and a half minutes and measured about 7.8 on the Richter scale (7.9 on the moment magnitude scale). There were 525 aftershocks recorded in the following two weeks. The main shock could be felt in much of the lower half of the North Island.

Bay of Plenty

In May we commented that over the previous two months there had been a cluster of earthquakes around an area called The Vents, a geothermal area between White Island Volcano (presently at alert level 1) and Whakatane in the Bay of Plenty:

In August 2006 experts at the Natural Hazards Management Conference in Christchurch warned that Rotorua, Taupo and Whakatane are set to be wiped out in a massive, long overdue earthquake and that people should be prepared for a catastrophic event:

“Geology experts Tim Davies and Mauri McSaveney have predicted that an alpine fault earthquake is overdue, and would result in the East Cape ripping away from New Zealand, destroying the plateau that Rotorua is based on and taking Taupo and Whakatane with it.

The pair say the earthquake will strike “out of the blue” and cause widespread death, shut down power generators, create tsunamis within New Zealand and overwhelm emergency services.

“The most likely time [for the quake] is now. The next most likely time for it to happen is tomorrow,” Associate Professor Davies, of Canterbury University, told the conference.

“It will occur with no recognisable warning. We can’t manage it – we have to adapt to it.”

The pair have outlined a nightmarish scenario in the aftermath of the quake and are urging people to be prepared as best they can. Overseas help would be needed when the quake struck…

The interval since the last event (in 1717) is longer than any interval between known earlier events.

Rotorua historian Don Stafford said the experts’ predictions were probably right and residents should be prepared.

“Who else could you listen to other than an expert. They have their reasons for why they believe they are worth listening to.”

Mr Stafford said historically there had been major eruptions and earthquakes in the Central North Island, with the most recent being Mt Tarawera in 1886.

“Lake Rotorua was a gigantic eruption 230,000 years ago. There have been gigantic eruptions for thousands of years.

“The historic massive eruption of Lake Taupo was recorded in China, Rome and Italy.”

Mr Stafford said the Central North Island had been relatively quiet during the past few decades.

“We have had it pretty sweet and I don’t doubt for one minute that there will be more big eruptions. … We would be foolish to presume that it won’t happen just because we are living here.”