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On 12 April at 7:41am, an earthquake with a magnitude M5.2 struck at a depth of 24km, approximately 15km west of Masterton in the Wairarapa. 

Last updated: 1:45 p.m, 12 April 2016

Facts about the earthquake

A strong earthquake occurred at 7:41am New Zealand time, 15km east of Masterton, approximately 24km deep. So far we have received over 2,800 felt reports, primarily south of Taranaki and Hawke's Bay through to the top of the South Island. The highest level of impact from our felt reports so far has been MM6 ("strong"), at which level small items fall from shelves and there can be movement of small appliances. Scattered reports of this intensity were received from places in Whanganui, Manawatu, Wairarapa and Wellington.

The earthquake occurred within the descending (subducting) Pacific plate. The movement was normal faulting.

Aftershocks

Thus far there have been over 50 aftershocks, none bigger than M3.8, and it is expected this will continue but lessen throughout the day.

Initial magnitude

The initial magnitude of M3.1 soon found its way to the more correct magnitude of M5.2. A small foreshock was mixed in with the main quake, causing this to happen. Email and GeoNet quake app notifications were affected by this, sending out their notifications based on the smaller magnitude estimate.

WHAT TO DO DURING AN EARTHQUAKE

Drop, cover and hold during an earthquake

For more advice on positive actions to take before, during, and after an earthquake, go to Civil Defence's: get ready get thru.

A further small swarm of earthquakes as occurred south of Rotorua in the Te Kopia area. This swarm lasted about 6 hours on Sunday 20 March.  We recorded 23 earthquakes that are large enough to get locations. The earthquakes range from Magnitude 1.3 to Magnitude 3.0, while the depths ranged between 3 and 8 kilometres. The majority of these earthquakes are about four to six kilometres deep.

This swarm is similar but smaller than the one near Waikite Valley on from 21 to 25 February. Swarm activity like this is very typical of earthquake activity in the Taupo Volcanic Zone, where earthquake swarm activity is very common.  

So what is a “swarm”? 

Swarms are often characterised by no one main or large earthquake, with many of the earthquakes being about the same size. Ten of the earthquakes in this swarm are larger than M 2.0, while 13 are smaller. Some earthquakes are so small we can’t locate them with our equipment currently.  

Local residents have reported feeling these earthquakes. However, these earthquakes are too small to be widely felt or cause any significant damage.  The Waikite Valley-Te Kopia area is about 20-30 km from Rotorua and is characterised by many active faults. GNS Science geologists have mapped numerous active faults in the area. The largest is the Paeroa Fault. It can be traced for over 25 km and has a vertical offset of over 500 m. Many earthquakes occur in this area. GNS Science continues to monitor all activity throughout the Taupo Volcanic Zone.


We’ve continued our analysis of the earthquakes from last night and the location has moved back to the original review from the Duty Officer. This means the M 5.0 earthquake is shallower, as per the original review (10 kilometres deep), which was completed within eight minutes of the earthquake occurring. Another earthquake, shortly after the M 5.0, which was a M 4.7,  shows that both were strike-slip earthquakes, meaning there was a side-to-side movement. We’ve already had a number of aftershocks and these will continue but likely won’t bring any damaging shaking.

We’ve sat down and chatted with two of our paleo-seismologists, Russ Van Dissen and Robert Langridge, who are experts in the faults of the North Canterbury and Marlborough region.  Current research studies are being undertaken on these faults in Northern Canterbury and Marlborough Fault system by Russ and Rob as part of a joint New Zealand and US-funded NSF project that looks to understand the role of the Clarence among three other major faults in Marlborough.

“North Canterbury is historically and geologically very active when it comes to earthquakes. We’ve got a number of large, active faults running through that part of the South Island,” says Rob Langridge.

Bill Fry, one of our seismologists says this area is known as the transition zone.

”This area is known as the “transition” zone from the Hikurangi Subduction Zone to the Alpine Fault system.  The tectonics in this area are active because of the change between these two systems. Because of this transition zone, earthquakes this size and larger are relatively common and are spread over a wide range of depths.”

 

Some larger historic quakes in this area include earthquakes in 1848, 1888, and 1968, among others. You can find out more about the larger earthquakes using our QuakeSearch.  

The earthquakes have occurred near the Clarence Fault. However, due to the low number of seismic stations in this area and the uncertain location of the Clarence Fault at depths greater than a few kilometres, we cannot confirm that the earthquakes happened directly on this fault but it is the closest larger fault near the epicentre.

Increased earthquake activity is likely in or near this area until the sequence decays. We should take this opportunity to always remember that when an earthquake happens, the chance of another earthquake in the same region increases.  However, earthquakes can happen anywhere in New Zealand. If you live in New Zealand, the best thing you can do is be prepared for emergencies. Here is more information about how to prepare:

 

 

Quakes by the numbers

Have quakes been increasing?

We're hearing this question more and more, so I thought I'd pull together our quake numbers into a few graphics and let the numbers speak for themselves. January and February this year are on par with many other previous months. There has not been a substantial increases in quakes, especially when you look at quakes about magnitude 3.

Quakes I looked at:

I looked at quakes close to New Zealand from January 2012 to March 2016, and broke them down by their month, magnitude, and depth. You can see that there are fluctuations in quake numbers over the years. Also obvious is the impact that large, shallow quakes - like Seddon and Cook Strait - have on overall quake numbers, as they produce aftershocks. The circles in the bottom left show the relative numbers of quakes by magnitude. The amount of magnitude 2 and smaller quakes make up the vast majority of the quakes we record. The real number of quakes smaller than magnitude 2 will be much higher than this - we know our network can't record them all.

The United States Geological Survey recently looked global earthquake numbers and found they were on par for 2015.

Unfortunately, this is my first experimentation with this graphic application and it turns out it doesn't work very well on mobile (which is commonly a large percentage of our readers! sorry guys, you can click on the mobile link below).

Infographic for mobile users.

A small swarm of earthquakes, which began on 21 February, has been recorded in the Waikite Valley, near Rotorua. Most of these earthquakes are currently occurring in Waikite Valley, about 20 kilometres south of Rotorua. So far, there have been more than 50 earthquakes. The earthquakes range from Magnitude 1.0 to Magnitude 3.4, while the depths ranged between 5 and 8 kilometres. The majority of these earthquakes are about six to eight kilometres deep.

There have been two earthquakes of Magnitude 3.4, the first on 21 February at 3.26 am and the second on 25 February at 11.01 am. This is very typical of earthquake activity in the Waikite Valley area, where swarm like activity is common.  

So what is a “swarm”?

Swarms are often characterised by no one main or large earthquake, with many of the quakes being about the same size. Only eight of the earthquakes in this swarm are larger than M 2.0, while 26 are between M1.5 and M2.0. Some earthquakes are so small; we can’t locate these with our equipment currently.  

Several local residents have reported feeling these earthquakes. However, these earthquakes are too small to be widely felt or cause any significant damage.  The Waikite Valley area is about 20 km from Rotorua and is characterised by active faults. GNS Science geologists have mapped numerous active faults in the area. The largest is the Paeroa Fault. It can be traced for over 25 km and has a vertical offset of over 500 m. Many earthquakes occur in this area. This swarm is highly unlikely to be associated with volcanism - GNS Science continues to monitor all activity throughout the Taupo Volcanic Zone.

This morning was another rude reminder that the Canterbury Earthquake Sequence is still on-going in Christchurch. This earthquake was in a different part of Christchurch than the Valentine’s Day earthquake and was strongly felt by several thousand residents who filled in Felt Reports.

These earthquakes can be demoralising and unsettling for some people. You are perfectly normal if you find these are events unsettling. The All Right? website is a great resource where you can talk about any anxieties or concerns that you have regarding the earthquakes. 

Now, to the science…

About the Leap Year Earthquake

The earthquake woke Christchurch residents up at 3:32 a.m. this morning. Even though it was “only” a M4.3, it was very shallow at five kilometres deep, and directly under the Christchurch suburb of Cashmere. This would have made it particularly strong for those nearby. We’ve taken a close look at the Peak Ground Acceleration (horizontal) and have compared it to the Valentine’s Day earthquake here:

A PGA of 0.2 is similar to what would have been felt in Wellington during the Cook Strait Earthquake. Note: the lines on this map are indicative of ground shaking. This is not an exact replication of all areas that would have felt the earthquake.

As the map illustrates, this earthquake would have felt just as strong as the Valentine’s Earthquake for those west and south of Cathedral Square. For those in Eastern and Northern Christchurch the Valentine’s Day quake would have been much more intense. 

So what have we been doing since the Valentine’s Day Earthquake?

Well, since you asked…quite a lot! Since the Valentine’s Earthquake, our scientists have been active in Christchurch. 

Here is a video (check out that drone action!) on the science response:

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Also check out our updated forecast page. There is a new feature at the bottom of the page which is table that compares all the PGAs, magnitudes, locations, depths etc…for the 14 M5.5 and above earthquakes since the Darfield earthquake in 2010.


 

On Sunday, a magnitude 5.7 earthquake struck offshore from Christchurch. Once the ground stopped shaking, our science response kicked into high gear. We are throwing all the science we got at this newest member of the family of large earthquakes in Canterbury. Our scientists have been spending the week running models, gathering data (some of it from space) to look at the Valentine's Day quake in-depth. We got an enormous amount of information from this quake and we are still making sense of all it.

First off the block, we determined that the location needed further refinement. Our best seismologists and geodesists have been hot on the case, each of them using a slightly different way to look at the quake, including data from our GPS and data from space (InSAR).

We now have a more exact location and depth for this earthquake. It is closer to shore (2 kilometres away) and shallower (8 kilometres instead of 15) than our initial review [see image]. The magnitude is still the same. This shift in location better aligns with the accelerations that were recorded, as well as the extent of the liquefaction activity and rockfalls. 

Investigating the Earthquake

Our group of scientists have taken extraordinary measures already, individually and as a team, to learn as much as we can as quickly as possible. We know how important it is to people in Canterbury to provide the fastest and most robust information we can about these quakes. Here's our scientists talking about how they go about their contributions to understanding this new chapter of earthquakes in Canterbury:

Our Scientists:

Dr Sigrun Hreinsdottir - GPS

Q. Tell us about the science that you are doing now based on the Valentine's Day Earthquake?
A.When you have an earthquake the whole surroundings move. We take measurements from continuously running GPS stations which record how the earth moved at the surface. From that information we can infer how the fault moved under the earth during the quake, as well as pinpoint where the earthquake happened. This is completely independent from how the seismologists calculate the same parameters. Additional stations are occupied and measured every year in Christchurch, and this annual campaign had just wrapped up when the earthquake struck. They were therefore able to go out again and take measurements days following the quake to record how each station has moved as a result of the quake.

 

Q. How does this research compare to what you could do five years ago?
A. Before the Canterbury earthquake sequence, we had  fewer continuous GPS stations. We try to cover all of New Zealand, so the emphasis has been on the regions that are most active. In response to the 2010 and 2011 earthquakes, the network around Canterbury has grown to gather as much data as we can.

Dr Ian Hamling - InSAR

Q. Tell us about the science that you are doing now based on the Valentine's Day Earthquake?
A. At the moment I'm taking the measurements from 13 GPS stations around the earthquake, and using them to generate a model that can recreate movements at the earth's surface. That will then give us an idea of the size of the fault that moved and how much it moved by. 

I'm also using data retrieved from space. This is called InSAR data, gathered from satellites in orbit. Every time the satellite passes over New Zealand it sends out pulses of radar energy. These pulses bounce off the earth's surface and are recollected by the satellite and put together as an image over the region. Changes in images before and after Valentine's Day would be caused by the earthquake. The Valentine's Day earthquake is on the smaller side of what InSAR can detect. At the moment from the preliminary results it looks as if there is a few centimeters movement along the coast which we should be able to detect with the radar measurements.

Q. What other things can InSAR measure?
A. There are loads of things you can do with InSAR. You can monitor earthquakes, volcanoes, subsidence from oil and gas operations. You can also look at geothermal subsidence. I've spent a lot of time on the Taupo Volcanic Zone and the whole region is subsiding 2cm a year. With InSAR you can generate large maps showing deformation over a wide area.

Dr Stephen Bannister - Relationships between the Earthquakes

Q. Tell us about the science that you are doing now based on the Valentine's Day Earthquake?
A. My work is all about determining the relationships these earthquakes and faults have with each other. We do this by re-examining the earthquakes in relation to each other and compare the earthquake waves from earthquakes that occurred several days or even years apart. We position those earthquakes in relation to each other to understand how the sequence evolves. In this case, the relationship between the aftershocks of this sequence and aftershocks that occurred in June and Dec 2011 as they are all located close to each other. The more we can understand the interrelationship between June and December 2011 and this week's sequence and other events, the more we can comprehend and understand that fault network. That way we can look at and interpret how the various faults are positioned in relation to one another.

Some of these faults may be in the same location as previous ruptures, but slightly deeper and slightly different orientations. So it seems like a very complex fault network and the answers aren't as straight forward as with other earthquake sequences.

Q. How does this research compare to what you could do five years ago?
A. All the approaches that we use are much tighter and more adaptable than what we were doing five years ago. 

Dr Caroline Holden - Strong Motion Data

Q. Tell us about the science that you are doing now based on the Valentine's Day Earthquake?
A. I'm looking at the fault rupture mechanism using very nearby strong motion instruments from GeoNet. We run different models, based on what the GPS is telling us. An earthquake starts at one point on a fault, and the rupture migrates along that fault. The models we run assume different fault orientations, directions of the rupture, and amounts of offset from the earthquake. When a fault breaks the surface, this work is much easier, as you can see the orientation of the fault there on land. But the earthquake needs to be large and shallow for the surface to rupture. Examples of this is the original Darfield magnitude 7.1.

Q. How does this research compare to what you could do five years ago?
A. This is the first time we've had a whole sequence that has been extremely well recorded. We have GPS, and InSAR, and heaps of seismograph stations. Because there are so many more stations now compared to five years ago, we can get better information. We've also learned that Christchurch is incredibly complex due to the variability of the soil. 

 

 

But wait... there's more!

We've made an updated decay curve to show how the Valentine's Day Earthquake has an effect on the overall Canterbury Earthquake sequence:

 

 

We also have a landslide team currently out in the field. They are scanning cliffs with lasers and flying drones around to get a better idea of what's happened due to this quake. When they're back in the office we'll share what they've found. We've also got our liquefaction team, as well as our social scientists assisting with the response. 

So, we are throwing all the science we got at this quake.

Our thank you list

There are many other players that contribute to this science:

  • InSAR images from the Japanese Aerospace Exploration Agency
  • Campaign GPS is carried out by Land Information New Zealand and University of Otago
  • Additional continuous GPS data is provided by companies Trimble (Geosystems network) and Leica (Global Survey)

 

A magnitude 5.7 earthquake has occurred at 1:13pm New Zealand time, 2 km east of Christchurch  approximately 8 km deep. So far we have received 3108 felt reports from Hawke's Bay to Invercargill. The highest level of impact from our felt reports so far has been MMI 8 in central and Christchurch. This is also shown in the coloured Shake Map to the right - which models shaking intensity in Modified Mercalli Intensity.

This quake is too small to have caused a tsunami.

Liquefaction

The highest recorded peak ground acceleration (PGA) from this quake was 0.4g (PGA is a good measure of the intensity of the shaking). For contrast, the highest recorded PGA from the February 2011 M6.3 quake was 2.2g, and in December 2011 M5.9 quake was 0.8g. Liquefaction in Christchurch often occurs when PGA is above 0.1g and we've had many stations in northern, central, and eastern Christchurch recorded PGAs above this level. This matches the reports that have been coming in of liquefaction is spots around the city.

 

Aftershocks

The last time Christchurch experienced a quake above magnitude 5 was nearly 4 years ago, with the magnitude 5.2 quake 20km east of Christchurch.

There have been aftershocks generated from this earthquake. At the time of writing (10:30am 15/2/16) there have been 105 aftershocks, the largest is a magnitude 4.2 quake, 10 km east of Christchurch.

Aftershock probabilities for the Canterbury region in the next year:

Please see the Canterbury Aftershocks page for the updated aftershock table.

 

 

 

 

What are our scientists up to?

  • InSAR (images from satellites) will be collected on Tuesday which was part of routine surveying of the region. GNS Scientist, Ian Hamling will be comparing these radar images to ones taken before the quake to look for signs of deformation caused by the earthquake.
  • GPS surveys were completed last week as part of an annual detailed campaign looking at deformation in the Central South Island. These campaigns are a collaborative effort between LINZ, University of Otago and GNS Science. Due to the earthquake, several sites near Christchurch are currently being resurveyed. This data may provide additional constraints on the deformation caused by earthquake.
  • GNS Science, in collaboration with Christchurch City Council, is organising surveys of cliff collapse and rock falls in the Port Hills this week following Sunday’s earthquake. These regions have been frequently surveyed since the Christchurch earthquake sequence began. Data will be collected by helicopter, remote controlled drones and groups of scientists and technicians on the ground.
  • GNS Science is also collaborating with EQC and Tonkin & Taylor to determine the extent and severity of liquefaction. GNS Scientist, Pilar Villamor, has been investigating historical liquefaction events to better understand why some regions, such as those along the Christchurch coast, are more susceptible to liquefaction.

As information from this work comes in, we'll let you know!

 

 

Last updated: 1:00pm, Monday 15th February 2016

A deep earthquake north-east of New Zealand shook people along the east coast of the North Island

As we've reported in the past, quakes of this nature also threw up a number of spurious "ghost quakes", which our duty team have since squashed.

Shaking from deep earthquakes along the subduction zone stretching from Kaikoura all the way up to Tonga is most focused at communities along the east coast of the North Island, plus there are usually a few reports from Christchurch and Banks Peninsula. It will have been a wobbly experience rather than a sharp jolt.

We'll be reassigning your felt reports from the deleted quakes to the real one - thanks for sending those in. If you're using our phone app, don't forget you can now quickly add a report there, too - no need to wait to be near a computer.

Earthquake swarms are very common in the greater Whakatane area. Since around 9 pm today (Sunday 24 January) the GeoNet seismometer network in the Bay of Plenty has been recording a swarm of small earthquakes. They locate about 3 kilometres north east of Thornton. We have been able to locate 15 during the last hour. Their magnitudes ranged from about M1.7 to M 3.3, while the depths ranged between 3 and 8 kilometres. The quakes are likely to be related to the long-term tectonic stretching of the Taupo Volcanic Zone.  They are not related to White Island.

The largest event occurred at 9.32 pm and has been reported as felt by 259 people. They have reported ‘moderate’ shaking (MM5), which is typical of events in this area. The events were too small to be widely felt or cause any significant damage. The largest events so far are near the middle of the swarm. Volcanologist Brad Scott commented that this is very typical of earthquake swarm activity, when many earthquakes are recorded over a short period of time.  Swarms are often characterised by no one main or large event, with many of the events being about the same size. Two of the events in this swarm are larger than M3. In the last 5 years we have located 115 earthquakes in this area larger than M2.5. The largest was M4.4 on May 19 2010.

The western Bay of Plenty coast area near Pikowai and Pukehina has been rattled by an earthquake sequence to day.  The sequence started this morning at 5.02 am when a magnitude 3.1 event was recorded. We have received 34 felt reports from the local community associated with that event. Since the first event we have recorded numerous small aftershocks (see drum plot below) and have been able to locate 15 of them, though many are too small to locate. They have ranged in size from M1.7 to M2.6 at depths of 5-7 km. This type of earthquake activity is common in the Bay of Plenty area.

In the last 12 months we have located 178 earthquakes in this area and almost 1400 in the last 5 years. Offshore of Pikowai has been busy, with about half of those been located in that area.  These earthquakes are occurring in an area about 12-14 km west of Matata, which was busy in the 2005-2008 period. We located over 2500 events in that earthquake sequence.

Today’s earthquakes appear more as a main shock-aftershock sequence, that is the largest event is at the start of the sequence and smaller events follow. In a swarm the largest event can be at the start, in the middle or near the end of it. Often we do not know until it is over if we are dealing with a main shock-aftershock sequence or a swarm. The area where these earthquakes are occurring lies just outside of the Taupo Volcanic Zone, the zone of active volcanic activity that extends from White Island (Whakaari) to Mt Ruapehu. Earthquake swarms are common in volcanic areas.

Earthquake swarms are very common in the greater Rotorua-Taupo area, known as the Taupo Volcanic Zone. Since around 3am today (Thursday 29 October) the GeoNet seismometer network between Taupo and the Tongariro National Park started recording a swarm of small earthquakes. They locate about 8 kilometres south west of Turangi. We have been able to locate over 60 of the events so far. Their magnitudes ranged from about M1.0 to M 3.4, while the depths ranged between 5 and 16 kilometres, with most being 7-8 kilometres deep. The quakes are likely to be related to the long-term tectonic stretching of the Taupo Volcanic Zone. Currently, there are no clear indications that the earthquakes are related to volcanic activity. As usual, we continue to closely monitor the nearby volcanoes to assess any changes.

The largest event occurred at 3.14 am and has been reported as felt by 12 people. They have reported ‘moderate’ shaking (MM5), which is typical of events in this area. The events were too small to be widely felt or cause any significant damage. The largest event so far is near the start of the swarm. Volcanologist Brad Scott commented that this is very typical of earthquake swarm activity, when many earthquakes are recorded over a period of time.  Swarms are often characterised by no one main or large event, with many of the events being about the same size. Four of the events in this swarm are larger than M3, another seven are larger than M2. The rest are smaller than M2.

In 2008 there was a similar swarm about 3-5 kilometres north of where this swarm is occurring, while in March this year there was one about 9 km to the north. 

Quake near Pongaroa

On October 12 at 21:05, an earthquake with a magnitude M5.7 struck at a depth of 24km 15km east of Pongaroa in the Manawatu.

Summary

The M5.7 quake  struck at 9:05 pm on a Monday evening, and was centered 15 km east of Pongaroa, under the south-east of the North Island. The quake was felt strongly in the North Island and we have received over 5000 felt reports from the public.  The focal mechanism shows it to be a reverse fault earthquake.

An aftershock sequence is ongoing following this earthquake and includes numerous magnitude 4 events. As with any aftershock sequence, we cannot rule out the possibility of occurrence of future larger earthquakes.

There were a few foreshocks earlier in the day, the largest being a magnitude 3.8 quake in the same location.

Like many parts of New Zealand the eastern Wairarapa is a seismically active region and has experienced many earthquakes in the past. In 1990 the region was shaken by the Weber earthquakes which were a series of three earthquakes with two larger than M6. This was followed by a M5.5 earthquake in 1992. More recently the M6.2 Eketahuna earthquake occurred to the west of the Pongaroa quake.

Current Research

The M5.7 earthquake likely occurred on the interface between the subducting Pacific Plate and the overriding Australian Plate. The earthquake was a thrust event indicating that the Pacific Plate moved deeper and to the west. The maximum recorded ground shaking was an acceleration of about 0.1g, compared with the 2014 Eketahuna earthquake which had a maximum of 0.26g.

What do we expect will happen next?

Based on the earthquakes so far and our knowledge of the tectonics, including the Hikurangi subduction fault, we have compiled the following scenarios that could occur over the following weeks.   

Scenario One - Very Likely (85% to 99% probability within 30 days)

Further aftershocks with magnitudes of less than M5.7 will occur and will decrease in frequency as time goes on.

Scenario Two - Very Unlikely (1% to 15% probability within 30 days)

An earthquake with a magnitude equal or larger than M5.7 will occur in the vicinity of the Pongaroa earthquake. This may be on a previously unknown fault in either the Pacific or Australian plates, or it may be on the plate interface. A larger magnitude earthquake, greater than magnitude 7, on the plate interface is extremely unlikely, however, as with many places in New Zealand an earthquake of this size can occur at any time. The chances of an M7+ earthquake occurring are temporarily increased by the Pongaroa earthquake.

There are two examples in the east of the North Island where a large earthquake was followed by an earthquake(s) of similar or greater magnitude. In the first example, a magnitude 7.2 earthquake in June 1942 near Masterton was followed by two subsequent events, a magnitude 6.8 in August and a magnitude 6.0 in December the same year.  

In the second example, a magnitude 5.9 earthquake in February 1990 near Weber and Porangahau was followed by a magnitude 6.2 earthquake in May 1990 in the same area, which damaged buildings near Weber.


GNS Science will continue to monitor the seismic and geodetic activity in the region.


Last Updated at 3:10 9m 13/10/15 - we will continue to update this story with further details.

 

The greater Rotorua-Taupo area is an active volcanic environment, characterised by geothermal areas, volcanoes, faults and frequent small earthquakes. Often the earthquakes occur as short lived cluster that are known a swarms.  Swarms are very common in the Rotorua-Taupo area. Larger ones will last weeks to months and include many hundreds of earthquakes. Larger and prolonged earthquake swarms are a common part of volcanic unrest. Overnight there was a small swarm in the Waimangu-Rotomahana area. The GeoNet seismometers recorded over 60 events and 20 are large enough to be located. The magnitudes range from 1.2 to 2.6, while depths ranged between 5 and 7.5 kilometres.  The events were too small to be widely felt or cause any damage. No felt reports have been received by GeoNet. Only weak shaking would have been experienced by the local population. 

Swarms are often characterised by no one main or large event, with many of the events being about the same size. Fourteen of the events in this swarm range M1.2 to M2.0 and six are larger than M2.0. The largest is M 2.6 and was the last event in the sequence. There are also many events too small to be located. This swarm is very similar to one on 15 January this year, when we located 19 events and the largest was M2.5.

A recent scientific paper by Dr Stephen Bannister and colleges has reviewed the earthquake swarm activity associated with the Waimangu-Rotomahana-Mt Tarawera geothermal field since 1990. They conclude sporadic swarms are common in this area and they typically only last 4-8 hours. The earthquakes are usually located in a 6 km long lineation that trends NE-SW from Lake Rotomahana and are related to the geothermal processes in the area. Last night’s earthquakes occurred in the same area.

The rapid detection and location of these small events demonstrates the capability of GeoNet to record this type of earthquake activity in these active areas. This helps under pin the volcano monitoring and allows the volcanologists to quickly assess the unrest, which in this case is very minor. In the last year there have been 204 locatable earthquakes in this area, which is normal.

Taupo Earthquakes

This last week has seen a spurt of small earthquakes north of Taupo. The larger events, which are located close to Wairakei were widely felt by the local community. The largest event with a magnitude of 3.7, occurred on 3 July at 11.58pm at a depth of 7km. We have received over 520 felt reports, which range from weak to strong. Light shaking (Generally noticed indoors but not outside; Light sleepers may be awakened; Vibration may be likened to the passing of heavy traffic, or to the jolt of a heavy object falling or striking the building) was reported by 501 people.

We have located 69 small earthquakes in this area north of Taupo in the last year. Nine of these were in the last week. These events are under the Wairakei-Tauhara geothermal fields and it is common to record earthquakes in this area. 


GeoNet is a collaboration between the Earthquake Commission and GNS Science.

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