Quake swarms near Lake Taupo

A map showing the locations of the swarm of quakes that occurred near Lake Taupo. Image: GeoNet

A swarm of 28 earthquakes has struck the country - and they all occurred in an area relating to volcanoes, faultlines and geothermal activity.

GeoNet's seismometer network recorded the swarm of quakes between Turangi and Lake Rotoaira, near the volcanic Lake Taupō, over the past week.

If you're wondering why you didn't feel them or haven't heard of them, that's because they ranged in magnitude from M0.4 to 2.2 - and in depth from 5-10 km.

The earthquakes were too small to be widely felt - the largest event in the swarm was reported as felt by only 13 people - or to cause any damage.

"Earthquake swarms are characterised as a cluster of similar-sized earthquakes, close together in time and location, usually with no one main or large event," says GeoNet.

IRREGULAR SWARM

"Earthquake swarms are common in an environment like NZ, more so in the Taupō Volcanic Zone (TVZ). The thing about swarms is how irregular they are," says GNS volcanologist Brad Scott.

"Some, like this one, lasted a couple of days. Others have lasted for years."

Quakes involved in swarms were often small - between M2 and M3 - but it was possible to get larger ones, and New Zealand has experienced clusters of quakes over M4.

"The usual cause is the prolonged ground deformation which can be driven by faulting process, they can also be driven by volcanic and geothermal processes. In some cases it can be a combination of the processes," says Brad.

In the latest swarm, the largest quake happened near the start, on September 18, and was followed by 10 smaller earthquakes that were more typical of a mainshock-aftershock sequence, according to GeoNet.

"Then about 24 hours later, on September 19, a further sequence occurred with the largest earthquake towards the end."

SHOULD YOU BE WORRIED?

Not in this case - the biggest quake in the swarm was only M2.2 and it was only felt by 13 people.

In general, swarm quake strength is also low - generally between M2 and M3.

A COMMON SWARM ZONE

Earthquake swarms are common in the area as the Turangi-Rotoaira area formed the southern portion of the Taupo Fault Belt, a zone of faulting within the TVZ.

The area is one of crustal extension, where the TVZ is getting wider.

Crustal extension is deformation of the earth's crust caused by movement of tectonic plates at their edges.

In the TVZ, the crust is being pulled apart at about 10 millimetres per year.

GNS Science geologists have mapped numerous active faults in the area, where earthquake swarms occur.

OTHER SWARMS

Recent examples of earthquake swarms include a cluster around Seddon in May, which began with an M3.8 quake.

Another swarm in late October 2017 centred around White Island, off the coast of the Bay of Plenty, including an M4.8 quake.

While they took place, GNS Science said they were more likely part of normal earthquake activity around the island than related to the volcano on it.

-Stuff/Leith Huffadine

You may also like....

0 comments

Leave a Comment


You must be logged in to make a comment.