New Zealand feels powerful aftershocks of M7.8 earthquake

Sizable aftershocks of up to magnitude (M) 6.5 have hit New Zealand following the M7.8 earthquake that struck South Island near Hanmer Springs in mid-November.

The M7.8 earthquake is considered by RMS Event Response Team to be the most damaging in mainland New Zealand since 2011, when a M6.3 earthquake hit Christchurch, killing 185 people and damaging about 100,000 buildings.

Robert Muir-Wood, chief research officer at RMS, said: “The November 13 earthquake was assigned a magnitude 7.8 by the United States Geological Service. That makes it more than fifty times bigger than the February 2011 earthquake, which occurred directly beneath Christchurch. However, it was still around forty times smaller than the Great Tohoku earthquake off the northeast coast of Japan in March 2011.”

In terms of damage caused, Muir-Wood added: “Although it was significantly bigger than the Christchurch earthquake, the source of the earthquake was further from major exposure concentrations.

“The northeast coast of South Island has a very low population and the earthquake occurred in the middle of the night when there was little traffic on the coast road. Characteristic of such an earthquake in steep mountainous terrain, there have been thousands of landslides, some of which have blocked streams and rivers – there is now a risk of flooding downstream when these “dams” break.

The M7.8 quake was felt from Christchurch on South Island to Wellington and as far as Auckland on North Island

However, damage from the aftershocks has been relatively light, according to catastrophe modelling firm AIR Worldwide, although main roads remain blocked from ground failure and landslides.

Numerous power outages have been reported, and water and sewer services have been interrupted in some areas.

The aftershocks have been distributed from the northern part of South Island, notably near Seddon and Kaikoura, to Paraparaumu and Wellington on North Island, which have experienced M4.9 temblors.

AIR said that seismologist expect the aftershocks to continue for a few months, with some temblors as strong as M5.0.

Although damage from the M7.8 temblor was lighter than what might have been expected, AIR said the earthquake and its aftershocks have widespread impacts, with glass broken in buildings, collapsed chimneys and structural damage reported.

New Zealand’s capital Wellington has seen windows broken and structural and contents damage in some multi-story buildings.

Multiple earthquakes have hit New Zealand in recent years, the worst of which in 2011/12, estimated to have eventually cost re/insurers almost $20 billion.