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GeoNet technicians experiment with Thermal Sensor Module for web cameras

Tue, 24/01/2017 - 11:27

Blog post edited by Brad Scott

Monitoring volcanoes has many challenges; a couple being how do we see at night and how hot is that vent we can see. Is it heating or cooling? One of the technologies that has helped us a lot is web cameras and another is handheld Thermal Infra Red (TIR) cameras. What if we had both in one unit! Web cameras work well in day light and when the lens is not covered in dust or sublimates from the volcanic plume. Recently the security industry has developed thermal sensor modules (TSM) to improve night views and these are now able to also run as ‘web cameras’. It doesn’t take long before our technicians could see the potential for volcano monitoring.

So where better to test this idea than at White Island, after all it is an active volcano. In fact our most active at present, last erupting in April and September 2016. Since we need to understand how volcanoes work and what they are up to is a big part of our monitoring it sounds perfect. A camera that works 24 hours would be a great tool. Even better if it can tell us something about the temperatures as well.

A TIR camera measures the emitted energy from the surface it is looking at, with more energy coming from hot surfaces than cold ones. The camera collects the data digitally and then applies a ‘false colour’ to make an image. One of the advantages is images can be collected at night (plus day), while our traditional web cameras see little at night unless the moon is out. The thermal sensor module will potentially give higher quality data with spatial coverage of areas around the vents as well and appears to be cost effective.

View of active vents in crater from South West rim View of Fumarole 0 View of active vents from North rim web camera site View of active vents in crater from rim

 

We recently took the thermal sensor module (TSM) to White Island to learn about the data quality, thermal range, spatial cover and the effect of steam and gas on the path between the sensor and feature we are looking at. We also plan to make use of it at other volcanoes and geothermal systems to learn about its capabilities. One constraint on all web cameras at active volcanoes is the lens has to be protected. For the TSM to work this has to be special material to allow the emitted energy (electromagnetic waves) to pass through. We are not sure how the acid rain will affect this. Just one of our many challenges. If we can make all this work it will improve our understanding of how volcano systems work and better inform us about the hazards and risks from volcanoes. 

 

View Online Brad Scott 2017-01-23T22:27:04Z

A new year, a new M7.8 Kaikoura aftershock forecast

Fri, 20/01/2017 - 13:25

Blog post edited by Sara McBride

20/01/2017 1.30 p.m.

We’ve been busy crunching the numbers based on all the seismic activity in the aftershock area of November’s Kaikoura Earthquake. So what’s the big news? The expected numbers of earthquakes have dropped a lot since the last forecast.  There is now a 25 percent chance of one or more M6.0-6.9 earthquakes occurring within the next month; this has decreased from 54 percent from our last forecast (19 December 2016).  We like this downward movement in our forecast; it is good step in the right direction. 

But does this mean we are all in the clear and don’t need to worry about more big earthquakes? No, absolutely not. Another big earthquake is still well within the probabilities in our models. A 25% chance in a month is still a concerning probability. We need to continue to be prepared for earthquakes as these will go on for years to come. The ongoing Canterbury Earthquake Sequence is an example of aftershocks that can last for years after the initial mainshock (which was the M7.1 Darfield quake in 2010). 

Remember: Drop, cover and hold in an earthquake. If the earthquake is long or strong and you are near the coast, evacuate as soon as the shaking stops. Our friends at the Ministry of Civil Defence and Emergency Management advise to not wait for an official warning or sirens.

What’s happened so far

We’ve had a total of 11956 earthquakes since the M7.8 Kaikoura earthquake stopped shaking our islands (we ran the numbers at 10 a.m. on the 19 January, so these will change). 452 of those earthquakes were M4-4.9, 53 were M5-5.9 and 4 have been M6.0 or greater. Yes, that is a lot of earthquakes but line up with what we’ve been forecasting.

Aftershock Forecast starting on 19 January 2017 

While no one can yet scientifically predict earthquakes, we can provide forecasts of future aftershocks (based on probabilities), as well as some scenarios from what is most likely to happen to what is very unlikely, but still possible. Most earthquake aftershock sequences decay (i.e. the number of earthquakes generally decreases) over time, with spikes of activity that can include larger earthquakes. Our previous forecast, from 19 December, is here

 

Average number of M5.0-5.9

Range* of M5.0-5.9

Probability of 1 or more M5.0-5.9

Average number of M6.0-6.9

Range* of M6.0-6.9

Probability of 1 or more M6.0-6.9

Average number of M≥7

Range* of M≥7

Probability of 1 or more M≥7

 

within 30 days

3.2

0-9

89%

0.3

0-2

25%

0.03

0-1

3%

 

within one year

16.6

7-29

>99%

1.5

0-4

77%

0.1

0-1

12%

 

Forecast for rectangular box with the coordinates -40.7, 171.7, -43.5, 171.7, -43.5, 175.5, -40.7, 175.5 at 12 noon, Thursday, 19 January. * 95% confidence bounds.

The aftershocks of the magnitude 7.8 Kaikoura earthquake are mostly occurring throughout a broad area from North Canterbury through to Cook Strait that surrounds the faults that ruptured in that earthquake, although a few have occurred in the lower North Island. We forecast aftershock probabilities for the area in the red box on the map to the right. The area near the centre of the box (around Kaikoura) is more likely to experience felt aftershocks than areas towards the edge of the box. See the MMI map below for more information on the forecast shaking for the Wellington area. Earthquakes can and do happen outside this box but the box represents the most likely area for aftershocks in this sequence. 

For example, there is a 25% chance of one or more M6.0-6.9 earthquakes occurring within the next month. 

The current rate of magnitude 6 and above earthquakes for the next month is about 10 times larger than what we would normally expect for long term seismicity represented in our National Seismic Hazard model. As the aftershock rates decrease, this difference will decrease as well.

Why has the forecast dropped so much?

There are two reasons to explain the drop in expected numbers: A month has passed since our last update and we have included another model into our forecast mix. The longer a sequence goes on, the more information we have (based on location, depth and size of earthquakes) to improve our forecasts based on what we are seeing from the Kaikoura earthquakes. We know more now and, as time goes on, we’ll continue to refine the models further to give you the best information we can. The more we observe, test, develop, and refine, the better we can forecast what happens next.

For example, for the 19th December forecast we estimated 8.4 earthquakes of M5.0-M5.9 within the next 30 days. With the updated model, that number for December would have been 5.2 earthquakes in the M5.0-M5.9 range; this was closer to the actual observed earthquakes of that size, which was three.  

Scenarios

The scenarios specifically address the probabilities of what we might see happen within the next year and were estimated in mid-December 2016. The scenarios cover a wider geographic area than the aftershock probability forecast area. The probability numbers in the table above are slightly different to the scenarios.  This is because we have used new information we have gathered from the slow-slip events, and their potential impact on the plate interface and other faults, to help define our probabilities in scenario three. 

There are very different probabilities for each scenario; some of these may be more unsettling to you than others. We recognise that while these scenarios may increase anxiety the best thing is to be prepared. Remember: To drop, cover and hold in an earthquake. If you feel a long or strong earthquake and you are on the coast, evacuate immediately.

Scenario One: Likely (approximately 70% within the next year)

The most likely scenario is that aftershocks will continue to decrease in frequency (and in line with forecasts) over the next year and no aftershocks of magnitude 7 or larger will occur. Felt aftershocks (e.g. over magnitude 5) can occur in the area from North Canterbury to Cape Palliser/Wellington.

Scenario Two:  Unlikely (approximately 25% within the next year)

An earthquake smaller than the mainshock and between magnitude 7.0 to magnitude 7.8 will occur. There are numerous mapped faults in the North Canterbury, Marlborough, Cook Strait and Southern North Island areas capable of such an earthquake. It may also occur on an unmapped fault. This earthquake may be onshore or offshore but close enough to cause severe shaking on land. This scenario includes the possibility of an earthquake in the Hikurangi Subduction Zone. Earthquakes originating from here or in the Cook Strait have the potential to generate localised tsunami. The Hawke’s Bay earthquake sequence in 1931 provides an analogy to scenario two, as a magnitude 7.3 aftershock occurred approximately 2 weeks after the initial magnitude 7.8 earthquake.

Scenario Three:  Very unlikely (5% within the next year)

A much less likely scenario than the previous two scenarios is that recent earthquake activity will trigger an earthquake larger than the magnitude 7.8 mainshock. This includes the possibility for an earthquake of greater than magnitude 8.0, which could be on the plate interface (where the Pacific Plate meets the Australian Plate). Although it is still very unlikely, the chances of this occurring have increased since before the magnitude 7.8 earthquake, and have also been also been slightly increased by the slow-slip events.

Initially our scenarios covered what might happen over the next 30 days, but we are now shifting to covering what might happen over the next year.  This is because the aftershocks are generally becoming smaller and less frequent (decaying) over time, and this lower aftershock rate increases the uncertainty of what might happen over shorter time periods. The change in forecast does not hugely affect the scenarios at the moment; we will review these again later in the year. While we will continue to update the aftershock probabilities regularly, we will not update the scenarios as often.

Can't get enough technical information? Here's the fine print on how we model aftershock probabilities.

Aftershock shaking forecasts
We have also calculated the probability of damaging earthquake shaking from aftershocks over the next year (starting 19 January 2017).  Damaging earthquake shaking is defined as MM7 on the Modified Mercalli Intensity (MMI) scale.  The MMI scale is different to earthquake magnitude – it describes the intensity and impacts of the shaking, which depend on the magnitude of the earthquake, how far away the earthquake was and the type of ground you are on.  At MM7 intensity shaking levels it is difficult to stand, furniture and appliances move, contents are damaged, there is minor building damage and liquefaction can occur in susceptible sediments.

The maps show the probability of MM7 shaking within the aftershock region, which includes Wellington. Over the next year the probability of MM7 shaking around the wider Kaikoura/northern area. In comparison, the probability of MM7 shaking in the Wellington area is around 3% (dark blue) in the next year. While this probability is considerably lower in Wellington than in the areas around Kaikoura, it is possible for shaking similar to what occurred during the mainshock to happen again in Wellington. 

Christchurch's aftershock probabilities are not greatly affected by the magnitude 7.8 Kaikoura earthquake.  The most recent update of the Christchurch aftershock probabilities are here. We update the Christchurch aftershock probabilities annually, as now they do not change much from month to month. 

Tsunami and landslide hazards

A tsunami was created by the magnitude 7.8 Kaikoura earthquake, and our scientists are still analysing the tsunami data and collecting information on its impacts. Remember, if an earthquake is too strong to stand up in, or lasts longer than a minute, move inland or to higher ground immediately. Do not wait for a siren or an official warning.

The earthquake also caused tens of thousands of landslides in North Canterbury, Kaikoura and Marlborough. These landslides remain dangerous and can move at any time. Please be careful around landslides and cracks in slopes. Heavy rain can pick up and carry landslide material and cause debris flows and debris floods (flash floods). Landslides have also dammed several rivers. These dams could breach, particularly in heavy rain. Please be careful and avoid riverbeds downstream of dams.

Take care of yourselves and others – physically and mentally

Earthquakes can be scary.  It is normal and okay to be a bit scared about things that are scary.  But the best thing you can do is take action and be prepared. 

You can follow our friends at the Ministry of Civil Defence & Emergency Management on Twitter and Facebook for the latest earthquake and tsunami preparedness information. You can also follow your regional Civil Defence Emergency Management Groups. If you are anxious about the earthquakes and this is affecting your ability to go about your daily life the All Right? Hotline (0800-777-846) is a great resource where you can talk about any anxieties or concerns that you have regarding the earthquakes. Remember to also seek support with friends and family, and to take time out to do things you enjoy.  

 


View Online Sara McBride 2017-01-20T00:25:46Z

Drones helps us keep a watchful eye on White Island (Whakaari)

Fri, 13/01/2017 - 12:19

Blog post edited by Brad Scott

In recent years Unmanned Aerial Vehicles (UAV’s) or, drones, as they are often called, have become a useful tool in going places that are often difficult or dangerous for people to go. We have been using them to make observations of locations that are not safe to visit and making maps of areas. In June we mapped the eruption deposits at Waimangu by UAV and more recently used them extensively to map the fault displacements and landslides produced by the M7.8 Kaikoura Earthquake.  In late December we were able to fly the active crater at White Island.

While we have the volcano cams on the island, these are stationary and don’t give us the kind of rich data that a drone can. Since the eruption in late April 2016 the vent area has often been obscured by steam and gas and a small lake also formed for a while. This made it difficult to fully assess the changes to the active crater area. We were able to work out the crater floor was lowered by about 13 m but couldn’t accurately estimate the volume of material erupted as we didn’t have a before and after map.  Understanding the volumes involved, distances material was moved etc. helps us better interpret the impacts and mechanism of the April eruption.

 

DTM (Digital Terrain Model) of the crater floor at White island

We were able to obtain images of the active crater area usually obscured by the gas and steam plume so we could make a new map and Digital Terrain Model (DTM) of the area. We know some of the crater floor was lowered about 13 m by the April eruption, but didn’t have any data on the vent area. During our visit in December we had a light easterly wind blowing the plume away from us and the humidity was low so the amount of steam was also low. Perfect conditions for flying the UAV mission over and in the crater.

Our UAV technician has processed the images and video captured on the day and is now compiling the DTM and surface maps. They are really impressive and are giving us a new insight to the changes within the active crater.

No word yet on what Dino thinks of this new visitor to the island. 

 


View Online Brad Scott 2017-01-12T23:19:49Z

Coastal uplift along the North Canterbury-Marlborough coast – results from the coastal survey team

Wed, 11/01/2017 - 11:14

Blog post edited by Caroline Little

Written by Kate Clark
Earthquake Geologist
k.clark@gns.cri.nz

 

Extensive coastal uplift occurred during the Nov 14 2016 Kaikoura earthquake. The uplift occurred almost instantaneously – all during the two minutes of shaking caused by the earthquake. 

Following the earthquake, a team of scientists from GNS Science and the University of Canterbury headed out into the impacted area to survey and record the amount of coastal uplift that occurred. Knowing the amount and pattern of uplift helps us understand aspects of the earthquake such as how much movement occurred across faults that cut across the coastline, and the presence or absence of offshore faults that also moved in the earthquake. Studying the uplift in the recent earthquake can also help us understand more about earthquakes that occurred in the past. For example, we can compare the amount of uplift that occurred in November 2016 earthquake with tectonic uplift recorded by uplifted marine platforms that were thrust out of the sea by earthquakes many thousands of years ago.

Our survey of coastal uplift showed that most of the coastline from Oaro to Lake Grassmere uplifted, that’s about 110 km of coastal uplift. The uplift varies along the coastline is broadly controlled by where faults ruptured the ground surface during the earthquake. The following paragraphs describe the pattern of coastal uplift from south to north along the coast.

Coastal uplift begins immediately north of where the Hundalee Fault crosses the coastline at Oaro. We observed the uplift from our helicopter surveys and also measured a point near Goose Bay where we recorded about 1.6 m of uplift. This amount of uplift is fairly steady along the coast toward Kaikoura. We measured a lot of points around the Kaikoura Peninsula and recorded about 0.8 – 1 m of uplift, which is consistent with the tide gauge there, which uplifted 0.95 m during the earthquake.

It was difficult to tell if uplift had occurred along the steep gravel beaches between Kaikoura Peninsula and the Hapuku River, but north of the Hapuku River uplift increased. Around Halfmoon Bay and Ohau Stream the uplift was measured at 2-3 m. The Hope Fault comes across the coastline near Halfmoon Bay and there was a small amount of surface rupture on the fault but the amount of uplift either side of the fault did not vary substantially. Just north of Waipapa Bay, two strands of the Papatea Fault cut across the coastline and the block in between these two fault strands was dramatically pushed up about 4.8 – 5 m high. This is the greatest amount of uplift recorded in this earthquake.

North of the Papatea Fault there appeared to be very little coastal uplift. Uplift increased markedly just north of where the Kekerengu Fault crosses the coastline. Uplift of around 2.5 – 3 m was measured at Needles Point, Ward Beach and Chancet Rocks. Between Chancet Rocks and Cape Campbell the amount of coastal uplift gradually decreased, there were a couple of sharp ~0.5 m steps where minor fault ruptures cut across the coastline. Around the corner from Cape Campbell, uplift was still moderate (~1 m) at Marfells Beach.

We noticed big changes in the coastal landscape each time we revisited locations, the uplifted seaweeds are quickly bleaching and falling off the rocks, and new hightide and storm beach lines are being established on the uplifted beach faces. This has been a phenomenal tectonic event and is causing numerous problems for local residents, fishermen, boat operators and other coastal users whose coastline has shifted so suddenly.  We are working closely with other scientists to build up a complete understanding of the earthquake, and also keeping in touch with our marine biology colleagues at the University of Canterbury who are working hard to understand the consequences and biological shifts that will be seen in the marine environment.

Uplifted rocks near the Waima/Ure River, approximately 25 km south of Cape Campbell. There was about 2.5 m of uplift here. Surveying neat Goose Bay, south of Kaikoura Peninsula. Uplift here was approximately 1.6 m. Long Point, approximately 10 km south of Cape Campbell. The uplift here was approximately 1.4 m. Kaikoura Peninsula from the air, uplift here was around 0.7-0.9m. This was taken at low tide and the dark brown fringe you can see around the edge of the rock platform is subtidal seaweed that prior to the earthquake would have been covered at low tide. Surveying coastal uplift at Cape Campbell, there was approximately 0.7 m of uplift here.

View Online Caroline Little 2017-01-10T22:14:18Z

2016 in review: The Groundbreaker

Sun, 01/01/2017 - 20:40

Blog post edited by Caroline Little

2016 is now officially sealed in the record books and...there is a lot to cover! This is going to a be a particularly long post. There was too much going on in 2016, so let me sum up: we had geysers, eruptions, landslides, tsunami and a whole lotta earthquakes. The ground broke under our feet, and that is why we are calling this year the “groundbreaker”. It should also be known as the "record breaker".

Let’s start with “this year in earthquakes” in New Zealand...

Earthquakes: a record-breaking year

This year had many earthquakes, but we are going to focus on the main two magnitude 7.0+ quakes that affected numerous communities: shaking our capital, Wellington, our weary quake-familiar Christchurch. Even our biggest city, Auckland, felt the sway of the East Cape earthquake. You’d be hard pressed to find someone who wasn’t impacted, in some way, by earthquakes in New Zealand this year.

 By the numbers, our monitoring network recorded 32,828 earthquakes this year. To give a point of reference, on average we record about 20,000 per year. Our other active year reached 29,000 in 2011. 2016 wins the dubious honour of most earthquakes ever recorded on the GeoNet network (we’ve been around for 15 years).  This year we had 122 earthquakes between magnitude 5.0 and 6.0,10 magnitude 6.0-6.9s, and, two magnitude 7.0 plus earthquakes. It’s been a geologically busy year. So let’s get into the earthquakes and their aftershock sequences that were the main contributors.

On the 2nd of September at 4.37 am, an M.7.1 earthquake struck 22 kilometres deep off the northeast coast of New Zealand. Luckily, the damage was minimal on land, although a small tsunami was generated.  A strong aftershock sequence continued in the days following.  Now, in any other year, the M7.1 would have been the biggest earthquake in New Zealand. But, New Zealand was just getting warmed up.

A little over two months later, at 12.02 a.m., the ground shaking began in North Canterbury, starting near Culverden. In two-and-a-half minutes, the earthquake moved across numerous faults, its seismic energy pooling and then overflowing onto one fault after the other, moving similar to the famous “Bucket Fountain” in Wellington. Along the way, the earthquake ruptured faults, tore through the earth and raised the seabed off Kaikoura.  From Christchurch to Wellington to Nelson, the whole part of the upper South Island and Lower North Island were impacted. Thousands of aftershocks have followed since the ground first shook. There is some pretty amazing video, taken by our Julian Thomson and starring Kelvin Berryman. Thanks, Julian and Kelvin! 

The M.7.8 Kaikoura earthquake will not go into the global history book of earthquakes because of its magnitude; the Ring of Fire regularly gets that size and much larger earthquakes. What makes it unique is two things: how it ruptured across the faults through the North Canterbury and Marlborough Fault areas and the slow-slip earthquakes triggered by M7.8. While we knew the faults were all there, we had only rarely seen an earthquake behave quite like this one.

Secondly, the slow-slip events or “silent earthquakes” started right after the M7.8 Kaikoura earthquake stopped. Our understanding of slow-slip earthquakes is evolving due to its relatively recent detection in 2002 in New Zealand. We don’t yet fully understand what it means to have slow-slip events triggered by the M.7.8. However, we are cautious as to what this might mean for future earthquakes. We’ve included these events in our probabilities and scenarios for this aftershock sequence. These two unique factors make this an earthquake of significance; New Zealand breaks new ground again!

 

It can be easy to get carried away by the excitement of the science of the earthquakes. However, the impact of these earthquakes is real and can be very painful for those who experienced it. Earthquakes, especially the large ones like East Cape and Kaikoura, can be anxiety producing; this is normal. Everyone responds to earthquakes differently, so if you are feeling unusually high anxiety due to the earthquakes, there are people here to help you through this time. If you are anxious about the earthquakes and this is affecting your ability to go about your daily life the All Right? Hotline (0800-777-846) is a great resource where you can talk about any anxieties or concerns that you have regarding the earthquakes. Remember to also seek support with friends and family, and to take time out to do things you enjoy. 

Tsunamis: the rehearsal and the real thing

This year, we were part of a national Ministry of Civil Defence and Emergency Management-led exercise regarding tsunami called Exercise Tangaroa. This exercise involved the whole nation’s civil defence groups and many other agencies across the country (link). Two days later, at 4 am, we had a striking coincidence with the M7.1 East Cape earthquake, which generated a small tsunami (30 cm). The residents near the East Cape earthquake did the right thing by evacuating immediately to higher ground.  

Two months after East Cape, when the ground shook again in Kaikoura, a localised tsunami was generated rising up to four metres from peak to trough that destroyed a cottage in Banks Peninsula.

Again, those who evacuated immediately on feeling the long and strong earthquake did the right thing.

If you are on the coast and you feel an earthquake that is long or strong, get gone.

2016 in Volcano Land

We asked our favourite volcanologist at large, Brad Scott, to give us the words for his thoughts on volcanoes in 2016. Here’s the lowdown from Brad: 

2016 saw a variety of activity from our active volcanoes, ranging from violent explosive activity to small-scale geysering and a mystery submarine eruption, creating a random pumice raft near Tonga. Also included was volcanic unrest, a hydrothermal eruption and remobilisation of old eruption deposits.

High-intensity rain in January saw debris (sand, clay and rock) left over from the 2012 Te Maari eruptions remobilised by the heavy local rainfall and washed out of the valley below the vents

Then, it was White Island (Whakaari)’s time. On Wednesday 27 April, a moderate steam and gas-driven eruption occurred at White Island (Whakaari). The eruption ejected the Crater Lake, created a new sub-crater, generated landslides/collapse and excavated some 13 m of the Crater Lake floor. This generated a very energetic blast that covered much of the Main Crater floor and the north-eastern portion of the volcano with some quite festively coloured green tinged ash. This eruption occurred during a period of volcanic unrest. However, we were challenged initially to confirm it had happened. These steam and gas driven eruptions do not give any useful warning. 

Mt. Ruapehu’s Crater Lake heated up, cooled back down and then promptly heated up again and then back down again. White Island had another hydrothermal eruption in September and then went back to simmering. Finally, we saw some pretty dramatic geyesing in Rotorua in the lake. The geysers had been pretty quiet for 15 years but decided this was the year to reawaken. 

Landslides: slips, slides and the smothering of State Highway One

The newest member of our public information team, Helen Jack, wrote up her thoughts on landslides. Helen is a landslide enthusiast, although she has a fond place in her heart for glaciers as well. She works out of our Dunedin office.

Landslides triggered by earthquakes took the (rather large) cake in 2016.  The M5.7 Valentine’s Day earthquake in February rattled down more rocks and cliffs along the eastern Port Hills in Christchurch.

Then, just as our landslides scientists were wrapping up almost six years of work shaken onto their plate by the Christchurch earthquake, the magnitude 7.8 Kaikoura earthquake delivered up an even bigger serving.  The earthquake caused over 80,000 landslides throughout North Canterbury, Kaikoura and Marlborough, damaging farmland, smothering State Highway 1 and the Inland Kaikoura Road in many places and damming several rivers. Heavy rainfall events throughout the year brought down landslides in the usual suspects of Haast Pass, Nelson/Tasman, Wellington and the Rimutakas, the Manawatu Gorge, East Cape and Coromandel.  Of course, a New Zealand summer wouldn’t be complete without an ex-tropical cyclone or two: In January Victor brought down landslides from East Cape to Tolaga Bay.

While landslides kept road crews very busy, and some property was damaged this year, we continue to be very fortunate that no lives were lost from landslides in 2016, particularly given the amount of landslides caused by the Kaikoura earthquake.

GeoNet turns 15

GeoNet also turned 15 years this year. In 2001, we started as New Zealand’s first national seismological monitoring system. In those 15 years, we’ve grown from a small fledgling network with a handful of online sites to more than 650 monitoring stations around the country, as far north as the Kermadecs and as far south as Antarctica.  You can read more about our 15 years of monitoring New Zealand’s geological hazards here.

(Caption: Sara Page, our public information specialist for social media, put the newsletter together detailing all the geological events that GeoNet has monitored in the last 15 years.)

2016: Ground-breaking but New Zealand still unbreakable

It was a challenging year but also inspiring to me about how we all pulled together. So while 2016 was a groundbreaker, it didn’t break us but rather pulled us closer together as a team.  This country faced some pretty big challenges, once again, due to seismic forces. And like the devastating events of 2011, people came together and helped out. Volunteers from all over the country came to assist Kaikoura, Ward, Waiau, and other affected communities in North Canterbury, Marlborough and Wellington.  It was a terrible year for those communities and people affected by these earthquakes.  We support those communities in their ongoing recovery.

For my part, working for GeoNet, I was overwhelmed with the support we received.  There were hundreds of “thank you” emails, tweets, and Facebook comments this year from people, which we really appreciate.  Further support came from our friends at the Ministry of Civil Defence and Emergency Management, who also work tirelessly this year. We couldn’t have done all the hard work this year without our supporters at EQC, LINZ, DOC, MetService and MBIE.

A couple of brief thank yous are required with a year like this one. Our technical support and services team diligently worked so we didn’t lose service during this challenging time, and our app and software developers helped us provide new and improved services. Our techs worked hard, putting up new temporary sites to better capture every ground movement in North Canterbury and around East Cape. They even found time to innovate with the new ‘Spade-tenna’ (patent pending). We certainly could not have supported GeoNet this year without our team of duty officers.  All of these people help support GeoNet. We thank them for their continued service to New Zealand’s geological hazards monitoring network.

2016 was also the year we said goodbye to our manager, Kevin Fenaughty, who had been in charge of public information since the beginning of GeoNet. Kevin left us this year one week before the Kaikoura earthquake for a new job in MCDEM. He sent flowers to say "sorry" but to be honest, we're still a bit grumpy about him leaving. Anyway, if you like our stories, you can thank Kevin because he hired us! So, thank you for your long service, Kev.  Also, Natalie Balfour, who was on the public information team for a short but very busy ten months, is now our data management team leader. She did a great job as part of the team but now has another big job in GeoNet. We wish both of them well in their new jobs.

So what will 2017 hold? I’d like to say that 2017 will be more like 2015: mostly harmless. But there are no guarantees; nature is a terrible project manager. Some years it’s almost too much while other years, it’s quiet. One thing we can say is that, at GeoNet, we are taking the lessons learned from 2016 and will continue to improve our network, our website, app, and all our services. We hope for a quiet, calm 2017 but the best thing we can all do is be prepared for whatever happens next.

To find out more here about how to prepare for emergencies, visit our friends at:


View Online Caroline Little 2017-01-01T07:40:21Z

GeoNet News Issue 22 - 15 years of big moments

Tue, 27/12/2016 - 22:15

Blog post edited by Sara Page

The latest issue of our publication 'GeoNet News' is here, and its a special edition for our 15th Birthday

 

Follow a timeline of important geological events in New Zealand from 2001 to 2016, along with some profiles of a few of our great team members. 

GeoNet News Issue 22.pdf

Previous issues can be found on the archives page

View Online Sara Page 2016-12-27T09:15:44Z

Standing in cracks and clambering up scarps – what have our earthquake geologists been doing?

Thu, 22/12/2016 - 15:56

Blog post edited by Helen Jack

Since the morning of 14 November earthquake geologists have been flying, walking, driving, and sailing all over North Canterbury, Kaikoura and Marlborough, mapping and measuring the faults that moved during the magnitude 7.8 earthquake.  It’s been a collaborative effort, involving scientists from GNS Science, NIWA, the Universities of Auckland, Canterbury and Otago, Victoria University as well as overseas researchers – 54 people in all!

The zig-zagged collection of fault ruptures mapped so far (click to see a bigger version)

This is one of the most complex on-land earthquakes ever recorded – to date, at least 12 faults have been mapped where they have broken through to the ground or sea floor. 

Unlike the cracks associated with landslides, these breaks start kilometres down in the crust, and come all the way up to the ground surface, shunting land sideways and upwards.  Some fault displacements are just wee steps or small cracks in the ground, while others have produced metres-high cliffs, or land has been pushed sideways by many metres relative to land on the other side of the fault.  New Zealand Geographic magazine has a great story about the fault ruptures and the geologists investigating them, with some amazing photos illustrating how the faults have moved.

So far, most of the fault mapping and has been done on foot, or by helicopter or drone.  Offshore, NIWA have used  a multibeam echosounder and high frequency sub-bottom profiler (fancy machines with interesting names that map the sea floor) on the Tangaroa to detect the movement on the undersea Needles Fault. 

The initial field reconnaissance of the faults has now finished, but LiDAR – a type of high-resolution ground mapping – is now being flown over much of the area affected by the earthquake.  And early in the new year NIWA scientists will be back out on a smaller boat the Ikatere, which can get closer to shore than the Tangaroa, to map how the onshore and offshore fault ruptures join up.

After taking a well-deserved break over the holidays, the geologists will begin analysing the mountain of data collected, to work out their piece of this earthquake story.  It’s likely that once the LiDAR and Ikatere data are analysed even more fault ruptures will be discovered, and they’ll then have a better idea of the total movement that has taken place.

Further down the track they’ll also be looking at the connections and gaps between the faults and what this means for seismic hazard modelling.  Is there evidence for these faults having ruptured together before? And is this normal?

We'll update you next year on this research, which gives us a window into understanding not only this earthquake but how New Zealand reshapes itself through earthquakes over millions of years.

A new kink in the landscape at the Papatea Fault, north of Kaikoura. Photo by Julian Thomson. The damage fault rupture can do - most of our buildings and infrastructure can handle quite a bit of shaking, but don't do so well when a fault ruptures through them. Photo by Jarg Pettinga.

View Online Helen Jack 2016-12-22T02:56:16Z

Landslides, dams, and a reminder to take care in the outdoors over the holidays

Thu, 22/12/2016 - 10:24

Blog post edited by Helen Jack

While uplifting land along the Kaikoura and Marlborough coasts, the magnitude 7.8 Kaikoura earthquake was also busy shaking a fair bit of land down.

The earthquake triggered thousands of landslides throughout North Canterbury, Kaikoura and Marlborough, and some of these dammed rivers and streams behind them.  Our landslide team have spent many hours mapping and monitoring these landslide dams along with staff from Environment Canterbury and Marlborough District Council, and colleagues from the US Geological Survey.

Going into the Christmas break there are still many potentially active landslide and rock fall areas, and landslide dams with water ponded behind them, from North Canterbury into Marlborough.  You'll need to be particularly careful if you are doing anything near a river, or heading into the back country in this area over the coming months.

 What are the landslides and landslide dams up to?

Area where landslides have occurred from the Kaikoura Earthquake. Mt Cookson Landslide. Photo by S Cox.

Over 80,000 landslides and rockfalls have occurred throughout North Canterbury, Kaikoura and Marlborough, particularly in the Seaward Kaikoura Range, the Amuri Range, the hills between the Inland Road and State Highway 1, and the lower country of the Conway, Leader and Stanton rivers.  Using helicopters, GPS, aerial photos and satellite imagery we’ve now mapped 196 places where landslides have dammed rivers, blocking or restricting the flow.  Many rivers have multiple dams – up to four or five in some cases.  Some of these dams are soft rock dams formed by large chunky slumps of soft mudstone, and some are hard rock dams formed by rock falls or avalanches (really large tumbly rock falls) of hard rock.

Most dams will break (fail) within a year by either overtopping and erosion during or immediately after heavy rainfall, or by internal erosion and collapse. Others may stay put and become permanent features with water running over or percolating through the dam (see our previous story to find out more about what landslide dams are and how they behave).  As there is yet to be any heavy rainfall since the earthquake the newly disturbed river catchments are yet to be put to the test. 

Most of the 196 mapped landslide dams are small and pose little risk, but we’ve been actively monitoring eleven landslide dams in the Conway, Gelt, Hapuku, Leader, Linton, Medway, Ote Makura, Stanton, Towy, and Waima catchments that could cause a flood wave and damage in downstream areas should they break.  Large lakes have formed behind the dams in the Conway, Linton and Hapuku catchments. 

Landslide on the Leader River. Photo by S Dellow.

One of the monitored dams on the Towy River, a tributary of the Conway River in the Amuri Range, has failed already.  One of the least stable dams, the water ponded behind it overtopped and cut a channel through the dam between 2 and 5 December, releasing a series of gravel-laden flood waves that reached about 1km down the river.

As well as monitoring the landslide dams, our scientists have been modelling how much downstream land could be flooded if the dams break in a worst case scenario (i.e. if the dam fails all in one go and all the water behind it is released). 

We’ve now handed over monitoring of the dams to Environment Canterbury and Marlborough District Council.  You can keep up to date with the latest on the Canterbury dams on Environment Canterbury’s webmap.

What you need to be aware of – in rivers, the back country and the coast

People should stay out of stream channels and river beds wherever possible from the Waiau River north to the Awatere River.  Landslide dams could fail at any time, but particularly during or immediately after heavy rainfall or an aftershock, creating a sudden flood downstream.  A lot of sediment is now flowing into river and streams, causing rivers to behave less predictably.  If you see one of your mates in their digger in the riverbed, you may like to politely point this out (once they are out of the river – don’t put yourself in danger).   Also, pitching your tent right beside a river is also probably not the wisest move – camping on an open elevated area is better. 

It may be difficult to tell if a landslide dam suddenly fails upstream.  Tell-tale signs include changes to the water colour (usually to a dirty brown colour) and strange or loud noises from the river valley.  These are cues to get out of the way. Landslide dams might not fail all in one go, so don’t assume that the danger has passed if there is a flood wave.   

Backcountry users should expect walking tracks and routes, and 4WD tracks to have changed significantly.  There are treefalls, landslides and rockfalls, loose rocks and cracks in the ground right through North Canterbury, Kaikoura and Marlborough and further landslides and rockfalls are likely during heavy rainfall or in an aftershock.  Some tracks are now covered with rock or sections have collapsed, requiring major work before they can be used again, and Barratts Bivvy in the Hapuku catchment was destroyed by a rock avalanche.  What may have been a relatively easy walk or drive may now be much harder and longer.  Streams and rivers may have new pools and rapids and vehicle river crossings, including entry and exit points, may have changed.

The Department of Conservation has closed all huts from the Seaward Kaikoura Range north to the Chalk Range, including the Clarence Reserve and the Isolated Hill Reserve (Sawcut Gorge).  These huts all need further earthquake damage assessments in the New Year, and access to them is also dangerous in places.

We recommend you check out the Department of Conservation website and have a yarn with local farmers about your planned route before heading into the hills.

People visiting the coast should also be aware of the potential for further land movement.  There were many landslides off the coastal hills and cliffs from the Waipara River to Cape Campbell during the earthquakes and rocks will continue to fall off these for some time.  Uplift of the seabed along this area may also have changed the depth of reefs or the pattern of rips and currents.

People-made dams

We’ve had few questions about farm dams.  The safety of farm dams is the responsibility of the dam owner.  If you have a farm dam you should check it for any damage and if you have concerns you should engage an engineer to investigate.  For more information you can contact Environment Canterbury or Marlborough District Council.

Updates

Staff at Environment Canterbury and Marlborough District Council are now monitoring the landslide dams and assessing how the increase in gravel in the rivers will affect future flooding. You can keep up to date with the latest developments on their websites. 

We plan to continue mapping and studying the landslides triggered by the earthquake throughout North Canterbury, Kaikoura and Marlborough over the coming months and will keep you updated on what we find.

 



View Online Helen Jack 2016-12-21T21:24:22Z

Updates on volcano visits

Wed, 21/12/2016 - 15:55

Blog post edited by Brad Scott

Over the last couple of weeks, the GeoNet volcano team has been busy making the most of the few fine days we have seen lately. We have visited Ruapehu and White Island to make a series of observations and measurements and collect samples.

White Island (Whakaari)

On November 21 we completed a gas flight at White Island, where we measure sulphur dioxide (SO2), carbon dioxide (CO2) and hydrogen sulphide (H2S). The gas output was down slightly on the October flight. The sulphur dioxide (SO2) has ranged 230-420 tons per day, carbon dioxide (CO2) 1240-1730 tons per day and hydrogen sulphide (H2S) 15-35 tons per day.

The main vent(s) were less audible than in October, still producing a transparent plume at the base/vent which evolved into a vivid white steam plume. There is no lake. Over the last 2-3 months the small lake let on the crater floor was disappeared to leave 5-6 small depressions, some have water ponded in them. The water levels are variable as are the colours of the pools, some are grey and active, others blue/green and passive.  We estimated the water levels varied by 2-3 m.

A levelling survey was completed on December 20 to ascertain the amount of ground deformation across the crater floor. Changes show subsidence (20 mm+) focused on the active crater area. Fumarole ‘Zero’ remains very hot, we measured 182 °C. It was 178 °C in October.

We used drones to obtain photography of the active crater area so we can build a new map. We also sampled the gases from the main gas plume using a drone. Maintenance was also completed on the web cameras.

Ruapehu

On December 17 we completed a gas flight at Ruapehu, our first successful flight for months. We measure sulphur dioxide (SO2), carbon dioxide (CO2) and hydrogen sulphide (H2S). The gas output was up slightly on the August flight. The sulphur dioxide (SO2) has ranged 19-22 tons per day, carbon dioxide (CO2) 240-640 tons per day and hydrogen sulphide (H2S) 0.6-1.6 tons per day since July.

The Crater Lake was visited to sample the water and collect gases on December 20. The lake temperature was 21.7 °C. Lake was a battleship grey colour with more blue grey water near the lakeshore due to meltwater going into the lake. The central vent was very slightly distinguishable in the right light conditions. The north vent area had a lot of sulphur slicks nearby.

Lake level appeared to be on the high side (summer melt) and the flow at the outlet was estimated at 60-80 L/sec.

Crater Lake temperature has been cooling since early October, when it reached 40 °C. For the last 2-3 weeks it has been around 24-22 °C.

Mercury Project:

As part of a collaboration with the University of Toronto (Canada) several passive air samplers are being installed on the active volcanoes and in large geothermal areas. These will measure mercury and its isotopes concentrations. The main purposes of the project are to characterize the sources of Mercury and monitor the spatial distribution of Mercury into the atmosphere.

Mercury samplers at White Island White Island active crater Ruapehu Crater Lake temperatures Ruapehu Crater Lake

View Online Brad Scott 2016-12-21T02:55:08Z

Papua New Guinea Earthquake 17 December 2016

Sun, 18/12/2016 - 05:01

Blog post edited by Natalie Balfour

Tsunami Threat cancelled

The Ministry of Civil Defence & Emergency Management (MCDEM) has cancelled the tsunami threat for NZ in place for all New Zealand coastal areas including the Chatham Islands that was issued earlier this morning after the magnitude 8 earthquake in Papua New Guinea at 11.51pm on 17 December. The tsunami expert panel has assessed the earthquake and determined there is no threat to NZ.

- Ministry of Civil Defence and Emergency Management


Tsunami Threat to New Zealand has been cancelled. A magnitude 7.9 earthquake occurred east of Papua New Guinea at 11:51pm Saturday evening (New Zealand Time). Please check the Ministry of Civil Defence and Emergency Management's website for the latest tsunami advice for the New Zealand region. The United States Geological Survey initially calculated the magnitude at 8.0, however they revised this down to 7.9 after some time.

 

Seismic Waves recorded across the GeoNet network from the M7.9 Papua New Guinea earthquake

View Online Natalie Balfour 2016-12-17T16:01:32Z

Papua New Guinea Earthquake 18 December 2016

Sun, 18/12/2016 - 01:53

Blog post edited by Natalie Balfour

Tsunami Threat cancelled

The Ministry of Civil Defence & Emergency Management (MCDEM) has cancelled the tsunami threat for NZ in place for all New Zealand coastal areas including the Chatham Islands that was issued earlier this morning after the magnitude 8 earthquake in Papua New Guinea at 11.51pm on 17 December. The tsunami expert panel has assessed the earthquake and determined there is no threat to NZ.

- Ministry of Civil Defence and Emergency Management


Tsunami Threat to New Zealand has been cancelled. A magnitude 7.9 earthquake occurred east of Papua New Guinea at 11:51pm Saturday evening (New Zealand Time). Please check the Ministry of Civil Defence and Emergency Management's website for the latest tsunami advice for the New Zealand region. The United States Geological Survey initially calculated the magnitude at 8.0, however they revised this down to 7.9 after some time.

 

Seismic Waves recorded across the GeoNet network from the M7.9 Papua New Guinea earthquake

View Online Natalie Balfour 2016-12-17T12:53:07Z

Did you see any evidence of the tsunami after the Kaikoura earthquake?

Tue, 13/12/2016 - 21:22

Blog post edited by Helen Jack

Everyone who self-evacuated after the magnitude 7.8 Kaikoura earthquake did the right thing. The earthquake triggered a tsunami and if it hadn’t been for the substantial coastal uplift in many places, and the low tide at the time, it could have been much more damaging.

Currently the only report of the tsunami impacting property was at Little Pigeon Bay on Banks Peninsula where a house was badly damaged. However, there are numerous reports of the sea leaving seaweed, shellfish and fish stranded above high tide level. There are also observations of the sea level falling below low tide, rising and falling quickly, and strange surges and currents.

If you, or someone you know, noticed unusual behaviour of the sea following the Kaikoura earthquake, or saw items damaged, or left high and dry by the sea, we would love to hear from you.  You can complete our online observations form at https://www.surveymonkey.com/r/Kaikouratsunami

There is still a lot to untangle about what happened in the Kaikoura earthquake – ten faults that ruptured and still counting! The tsunami is an important part of the whole picture. GNS Science are collecting observations of the tsunami to help understand what happened in this event and what might happen in future events.

Tsunami observations collected will be used in the New Zealand Tsunami Database entry relating to this event and may be used to direct further fieldwork to investigate tsunami impacts.  People’s observations are also really important for us to improve our knowledge of tsunami impacts and to calibrate our tsunami models.

GNS Science contacts: William Power, Ursula Cochran, Kate Clark, and Maureen Coomer

 

Sub-tidal shellfish found intact high on the beach near Needles Point. These are likely to have been washed up by the tsunami. Near Needles Point on the Marlborough coast that was raised by 2-3 m in the Kaikoura earthquake. The gravel in the foreground and abundant seaweed is likely to have been washed up by the tsunami. It reaches about 4.4 m above the tide level at the time

View Online Helen Jack 2016-12-13T08:22:41Z

How is the Kaikoura aftershock sequence behaving compared to the forecast?

Tue, 13/12/2016 - 12:22

Blog post edited by Natalie Balfour

13/12/2016 10:00 a.m.

Probabilities and scenarios…we’ve been getting a lot of questions about how these work and what it all means. Specifically, people want to know if the sequence is behaving as we have forecast.

So are we getting the number of aftershocks expected in the forecasts? The short answer is: we are on the low side of what we’ve forecast, but the numbers are mostly still within the forecast range.  There’s a bit more to the story, so let’s back up for a second and take a look at the big picture. 

How many aftershocks have there been?

By noon on Monday 12 December we had detected 8,735 aftershocks from the M7.8 Kaikoura earthquake (with the area of detection being the forecast area represented by the box). Most of these aftershocks have been small (8,669 earthquakes <M4.9) and would have only been felt close to the epicentre. As of Monday 12th December, there were also 49 aftershocks in the M5.0-5.9 range, and 3 aftershocks in the magnitude M6.0-6.9 range.

When a large earthquake like M7.8 Kaikoura occurs, aftershocks happen thick and fast. When that happens, our seismic detection network can miss smaller aftershocks as their energy is overshadowed by the larger aftershocks - so not all aftershocks are detected. Our seismic network is very sensitive and typically picks up even the smallest of shakes. But now, due to the big earthquakes coming through, it is more difficult to detect all of the quakes. Imagine a clear lake. Most of the time, when you skip small pebbles on the clear lake, you can spot the associated ripples easily. But then a giant rock is thrown into the clear lake. The splash and ripples it creates can cause the smaller ripples from the pebbles to go unnoticed. Once the giant rock’s waves subside, the smaller pebbles and their ripples become noticeable again. That is similar to what is happening here.

At this stage, we haven’t been able to detect all of the smaller aftershocks in amongst the waves of the larger earthquakes. Therefore, the total number of aftershocks in the earthquake catalogue below magnitude 5 is currently lower than what has actually happened. The total of 8,735 aftershocks is the bare minimum of what we’ve detected. When we have more time for data processing we will likely find further small aftershocks in the seismic waves of the mainshock. Our earthquake catalogue will be changed to reflect this in future.

 

 Observation and forecast time interval

M5.0-5.9

M6.0-6.9

M≥7

Date

Time

Duration

Forecast

Detected

Forecast

Detected

Forecast

Detected

14 Nov

00:15*

11.75h

14-32

24

0-5

2

0-1

0

14 Nov

12 noon

24h

5-17

12

0-3

1

0-1

0

15 Nov

12 noon

24h

1-10

4

0-2

0

0-1

0

16 Nov

12 noon

24h

1-10

1

0-2

0

0-1

0

17 Nov

12 noon

24h

0-8

0

0-2

0

0-1

0

18 Nov

12 noon

24h

0-7

1

0-2

0

0-1

0

19 Nov

12 noon

24h

0-6

0

0-1

0

0-1

0

20 Nov

12 noon

24h

0-5

1

0-1

0

0-1

0

21 Nov

12 noon

24h

0-5

0

0-1

0

0-1

0

22 Nov

12 noon

24h

0-5

1

0-1

0

0-1

0

         21 Nov12 noon7 days3-1910-300-1028 Nov12 noon7 days1-1310-200-105 Dec12 noon7 days0-1100-100-10

Total number of aftershocks by noon, 12 Nov

 

46

 

3

 

0

For example, at 12 noon on 14 November, we forecast that there would be between 5 and 17 aftershocks in the M5.0-5.9 range, for the following 24-hour period. Once this time period had finished, 12 aftershocks in this magnitude range were actually detected, which is around the average of what we forecast

Forecast and detected earthquakes for a rectangular box with the coordinates -40.7, 171.7, -43.5, 171.7, -43.5, 175.5, -40.7, 175.5. Note: Our aftershock forecast models are based on previous New Zealand aftershock sequences.   

* The first forecast is calculated is about a quarter of an hour after the mainshock to avoid the period of most undetected aftershocks.

How do the detected aftershocks compare to our forecasts?

At  the moment, the aftershock sequence is falling within or just below the lower end of our forecast range.  The table above shows the range in the number of aftershocks that we have forecast for 24-hour time intervals, compared to the number of earthquakes that we have actually detected so far, for three magnitude ranges.   

The  graph shows the number of aftershocks over M5.0 that we can expect per day, on average (with the uncertainty range in grey). The stars show the actual number of detected aftershocks that have occurred on each day. The graph shows that the forecast number of aftershocks will continue to decrease on average. There may be the occasional spike of activity as larger aftershocks occur with their own aftershock sequences. This follows the normal pattern of what we can expect following an earthquake.

We are working to understand why the Kaikoura sequence has been less productive than the average New Zealand earthquake sequence. However, the variability in aftershock productivity between sequences can be up to a factor of around ten. So far the aftershocks have decreased with the initial productivity of the sequence and as such the sequence is behaving normally.

In general, more small aftershocks will continue to occur than big ones. As a rule of thumb, there is a tenfold increase in the number of earthquakes for every one-magnitude decrease. For example, for one M6.0 earthquake, we expect around 10 earthquakes of M5.0-5.9 and around 100 earthquakes of M4.0-4.9 on average. This applies to all seismicity experienced, as well as that occurring as part of the aftershock sequence.

What does this mean?

In summary, the aftershocks are at the lower end of the forecast range. Just because we are in lower end of the forecast, it doesn’t mean that this will stay that way.

What you can do about forecasts: be prepared!

We know that these events can make people anxious or worried. That is perfectly normal; earthquakes can be scary! If you are feeling overwhelmed by the earthquakes or the forecasts, there are people who are there to listen and support you on 0800-777-846..

Our best advice is to be prepared for future aftershocks.  You can find out more about getting prepared by visiting our friends at the Ministry of Civil Defence and Emergency Management.

Can't get enough technical information? Here's the fine print. 

(This story will be next updated on the Monday 19th December, when the current weekly forecast period is over) 

 

View Online Natalie Balfour 2016-12-12T23:22:51Z

What do these slow-slip events mean for future large earthquakes?

Fri, 09/12/2016 - 15:44

Blog post edited by Natalie Balfour

Updated 3pm, 9/12/2016

This is an important, but difficult question that our experts here at GNS Science, along with Victoria University have been working on answering. The slow-slip events (or silent earthquakes) cover a large area of the plate boundary underneath the North Island and have made calculating the likelihood of future large aftershocks trickier.

Although still very unlikely, we now estimate that the probability of a magnitude 7.8 or larger earthquake in the coming year has increased to approximately 5% – due to ongoing slow-slip events. This is a small increase in the likelihood which is generated by the Kaikoura Earthquake alone. This is approximately 6 times greater than it was prior to the Kaikoura Earthquake.

Due to the large extent of slow slip, the adjusted forecast covers a larger region than the standard aftershock area to now include the lower half of the North Island and the upper South Island. There are several faults in these areas capable of large quakes, including the subduction zone and crustal faults like those that ruptured during the Kaikoura earthquake.

 
Cross section of the North Island of New Zealand showing how the
Australian and
Pacific Plates meet. The slow-slip events (orange-yellow
patches) are superimposed
onto the cross-section. Bottom right Insert
shows a map view of the slow-slip events.

What does this mean?

Our forecasts tell us what is likely (or unlikely) to happen in the future, but they can never definitively say if a large earthquake will occur or not. We’re aware that these messages could be unsettling, and that’s a very normal reaction. What we do want you to take away from this (and this applies to all New Zealanders, at all times—not only now) is to follow Civil Defence’s advice and make sure that you’re prepared for earthquakes and tsunamis. We know that being prepared makes a real difference in helping you get through an event and recovering afterward. Many of you have already got you and your family prepared, so well done you guys!

Tell me about slow-slip events again

The current slow-slip events that have followed the M7.8 Kaikoura earthquake are occurring along the fault between the Australian and Pacific Plates, known as the Hikurangi subduction zone.  The movements along the fault are equivalent to a magnitude 7.0 earthquake in the Hawke’s Bay-Gisborne region, and magnitude 6.9 earthquake in the Manawatu-Kapiti region.

We have observed many similar slow-slip events in these areas of this size, but this is the first time we’ve observed slow-slip occurring simultaneously in multiple areas around the North Island in the 15 years we've been detecting them. This is also the first time we’ve been able to observe slow slip in New Zealand after a magnitude 7.8 earthquake, so it’s possible this is a normal pattern after such a large quake.

The Hawke’s Bay-Gisborne region slow-slip event only lasted about a week, and it has mostly finished. Slow-slip events in these regions happen less than 15 kilometres deep. There were a number of earthquakes offshore Porangahau in the southern Hawke's Bay in the 2-3 weeks following the Kaikoura earthquake that were likely triggered by the east coast slow slip event.

The slow slip event beneath the Kapiti and Manawatu regions appears to be ongoing at a relatively steady rate since the Kaikoura M7.8 earthquake. Slow-slip events in these regions tend to occur between 25-45 kilometres deep.

If we can’t feel slow-slip events, why are you focusing on them?

Slow-slip events occur beneath the North Island, where the Australian and Pacific Plates meet. In the lower North Island, the slow-slip events happen slightly deeper than the part of the subduction zone where the plates are currently stuck together.  These “stuck zones” are thought to periodically rupture in large earthquakes. When slow-slip events occur, stresses are applied to this stuck-plate zone. This increased stress happens during all slow-slip events. The number of earthquakes during some slow-slip events can increase, but this doesn’t always happen.

There have been hundreds of slow slip events observed at subduction zones around the world that have not triggered larger, damaging quakes. So, if slow-slip events do trigger large damaging quakes, it is very rare indeed. In New Zealand we typically have at least 2-3 slow-slip events each year. Scientists have only discovered in the last 15 years that slow slip events occur, so trying to understand their relationship to larger, damaging quakes is still in its very early stages.

How did we go about incorporating slow-slip events into aftershock forecasts?

In New Zealand, scientists at GNS Science have been developing aftershock forecasts for the several large earthquakes since the Canterbury earthquake sequence. We’ve refined these over the last 6 years, but have never had to incorporate slow slip events into the mix.  

Experts from GNS Science and Victoria University evaluated many strands of evidence to determine the likelihood of an earthquake equal to or larger than the Kaikoura Earthquake. We have also consulted with several international experts who study slow-slip phenomena in their respective countries to provide additional perspective. 

This is our first run at including slow slip into the forecasts, and it is probably the first attempt worldwide to implement this, so it is definitely a work in progress and our estimates have large uncertainties. As scientists’ understanding of this phenomena improves we hope to develop better ways to incorporate the mechanics of slow-slip events and their relationship with earthquakes into our forecasts.

Being prepared

Civil Defence have great resources on how to prepare your home, how to make an emergency plan for your family, and what to do during and after an earthquake. Check with your local and regional council for your region's tsunami evacuation zones - remember, these zones apply regardless of where the tsunami is coming from. Knowing where these zones are can help you plan your evacuation route before a tsunami occurs.  You will not have time to do this if an earthquake occurs.  Remember if you are near the coast and you feel a long OR strong earthquake, then you should evacuate inland or to higher ground immediately.

As always, we'll keep you updated with any new information as it comes to hand. We'll also be updating our aftershock forecasts periodically. 

View Online Natalie Balfour 2016-12-09T02:44:49Z

Solomon Islands Earthquake 9 Dec 2016

Fri, 09/12/2016 - 08:39

Blog post edited by Natalie Balfour

Friday 9 December, 8:32 am – Tsunami Potential Threat Advisory for New Zealand has now been CANCELLED.

"We advise the public who intend to carry out activities in or on the water today, especially along the west coast of both the North and South Islands, that there could be strong and unusual currents for the rest of the day. Therefore, MCDEM advise people to stay out of the water."

- Ministry of Civil Defence and Emergency Management

Tsunami advice following the Solomon Islands quake

A magnitude 7.8 earthquake occurred east of the Solomon Islands at 6:38am today (New Zealand Time). Please check the Ministry of Civil Defence and Emergency Management's website for the latest tsunami advice for the New Zealand region. The United States Geological Survey initially calculated the magnitude at 8.0, however they revised this down to 7.8 after some time.

We will update this story as more information comes to hand

 

The earthquake was well recorded on all of the GeoNet seismographs:

View Online Natalie Balfour 2016-12-08T19:39:59Z

Landslides and Landslide dams caused by the Kaikoura Earthquake

Fri, 02/12/2016 - 13:56

Blog post edited by Caroline Little

Gelt River Hapuku River Upstream section of the Leader River Medway River Stanton River Waima River

One hazard we don’t often get an opportunity to talk about at GeoNet is landslides. That’s a good thing, we aren’t complaining. But with the M7.8 Kaikoura Earthquake, landslides and land deformation have been at the forefront of risk to communities living in North Canterbury and Marlborough.

Our landslide and paleoseismology teams quickly took to the skies to spot landslides in the Kaikouras and Southern Alps. After clocking hours upon hours in the skies, we estimate that there has been between 80,000 to 100,000 landslides triggered by the Kaikoura earthquake and aftershocks.

What we know so far

Certain areas have more landslides than others. In our flybys, the landslides begin just south from Cape Campbell, becoming more intense south of the Clarence River, with several large (100,000 – 500,000 m3) landslides disrupting both State Highway 1 and South Island Main Trunk railway (e.g. Ohau Point and Waipapa Bay areas). South of Kaikoura, on the steep slopes near Twin Tunnels, damage was similar to areas north of Kaikoura, again covering and or disrupting both State Highway 1 and railway.

What are landslide dams?

A landslide forms a dam when the debris from the landslide blocks a stream or river. There are two parts to a landslide that dams a river, the landslide itself and the lake or pond that forms because of the landslide blocking the watercourse. There is a complex relationship between dam size, lake volume and landslide type that determines whether or not a dam will fail. Every landslide dam differs in terms of size and composition, so their behaviour over time varies. Landslide dams can last from a few minutes through to thousands of years. Failure modes of landslide dams include overtopping and headward erosion (when the downstream side of the dam erodes), piping (water flowing through the dam) and additional slope failure, particularly into the newly formed lake.

If a landslide dam rapidly fails, the flood wave of water starts off high near the dam, and rapidly lowers as it moves downstream.  Alternatively, the dam may also gradually erode and the water level in the lake will decrease relatively slowly with no flood peak travelling downstream.

Since the earthquake happened, GNS Science has been working to compile a complete inventory of landslide dams in the area affected by landslides after the earthquake. This work involves using remotely sensed (satellite) imagery, and a systematic search for landslides by flying over affected areas to locate landslide dammed lakes. So far 42 landslide dams have been identified and we expect to find a few more small ones.

Where are the landslide dams?

There have been 150 landslide dams identified so far in the Kaikoura area, most of these dams are small and pose little risk. However, we are monitoring 11 landslide dams because the may pose a risk to areas downstream (these 11 are Conway, Gelt, Hapuku, Leader upstream, Leader downstream, Linton, Medway, Ote Makura, Stanton, Towy, Waima). The landslide dams with the highest level of hazard are currently:

  • Linton Stream, which has a large, leaking dam with a lake behind it
  • Conway River (lower dam) – water is flowing through the dam which is helping to lower the lake level behind it, but there is still a potential for failure
  • Hapuku River – the dam is formed by a rock, sand and silt avalanche. The lake is filling so the hazard will increase through time until it is full.

For maps and more information have a look at the great work Environment Canterbury have published

Safety around Landslides

Please take precautions and stay away from landslides and landslide dams. Stay away from steep cliffs and slopes in the Kaikoura and Marlborough region in case of rockfalls. 

Director of the Ministry of Civil Defence and Emergency Management, Sarah Stuart-Black, advises that people in areas downstream of landslide dams to be especially vigilant and to keep clear of river flood channels and outlets. Further safety information is provided by the Canterbury Civil Defence and Emergency Management Group.

For more information from the Ministry of Civil Defence and Emergency Management, go to http://www.civildefence.govt.nz/.

What causes a landslide dam to fail?

The likelihood of dam failure is higher during periods of steady or intense rainfall, and for about 24 hours afterwards. There is more likely to be a rapid dam failure if there is a lot of water upstream of a small dam, whereas rapid dam failure is much less likely if there is a just a small amount of water upstream of a large dam.

Landslide dam failure

There are three different options for how long landslide dams last. These data are general and apply to all of the dams, so we can’t give any specific information on what might happen at each of the dams. At this stage, none of the dams look like they will overtop their river flood banks if they do fail rapidly. If rapid failure occurs without being associated with heavy rainfall then the level of the water will probably be a maximum of the level experienced during a 1 in 10-year flood - but no warning will be given.

Short lived landslide dams. Over half of dams (about 56 percent) fail within a month after forming. In this case, the dam remains in place until it is rapidly overtopped by water. Rarely, the dam may fail more slowly. The time between the dam overtopping and rapid failure can be between days and a month. As an example of rapid dam failure, the Poerua River dam failed in 1999. While this example shows what has happened in the past when a landslide dam rapidly failed, it’s important to note that this dam is larger than any of the dams seen in the Kaikoura area.

Medium lived landslide dams. Almost a third of landslide dams survive the initial overtopping but then eventually either fail rapidly because of downward or headward erosion, or fail slowly as water permeates through it, removing sediment over time until the dam has gone.

Long lived landslide dams. Some dams become a semi-permanent or permanent feature, forming a lake behind the dam. Examples of this are the Young River dam and the dam at Lake Waikaremoana, which formed the lake itself. Both of these dams are much larger than any of the dams seen in the Kaikoura area.

The percentages in the above descriptions are from Costa and Schuster (1988).

On-going assessments of landslides and landslide dams

As the landslide data comes in it is being used to undertake dam-break modelling, which will help determine what will happen if a dam fails rapidly. This modelling is used to determine where the flood wave from rapid failure will go assuming normal river flow conditions. From this people and assets at risk can be identified and management plans put in place.  

Landslide specialists at GNS Science are working hard to confirm the initial assessments, model the landslide dams, and determine what might happen if they fail. The information on this page will be updated as more data is collected and our understanding increases.

Ote Makura Stream Linton River Downstream section of the Leader River Conway River Towy River

View Online Caroline Little 2016-12-02T00:56:01Z

Tech Tales: Calling a spade…an antenna?

Wed, 30/11/2016 - 14:11

Blog post edited by Caroline Little

They say that necessity is the mother of invention and our tech “ninjas” found that out in…erhm…spades during the latest response to the M7.8 earthquake. 

Andrew Cowie setting up the SpadeTenna™

After the M7.8 Kaikoura earthquakes, our techs quickly took to the air to put in more temporary sites throughout the Kaikoura Mountains and Southern Alps.  The problem with these locations is its remoteness and sustained damaged to cell towers from the earthquake.

Now, when our techs go out into the field, they can only take the most important items with them due to limited space on the helicopters.  Our techs are dropped off into the middle of nowhere with few supplies to make these temporary sites. Think “Survivor” but with a radio, some seismographs and a couple of muesli bars. Our techs are able to put in these temporary sites in a matter of hours.  

The lack of space has made our techs…become creative in their use of tools. Recently, they realised their antenna needed more height to communicate with base. They cleverly repurposed a spade (used to dig out ground to place the site in) and used electrical tape to put the antenna on the spade. BOOM: instant communication tower. The Spade-tenna© (patent pending) was designed to elevate the antenna in order to increase cellular signal strength in remote locations. This means we don’t lose contact with these sites.

They quickly put up 9 temporary sites since the earthquake stopped shaking, 4 with the clever spade-tenna.

Tim McDougall, one of our techs, said they were proud of their latest innovation but that they are now running out of spades…

A big shout out to our techs because these sites are a critical part of our ongoing monitoring of the M7.8 Kaikoura aftershock sequence. We couldn't be GeoNet without the people looking after our 600 plus monitoring sites throughout New Zealand.   

It's not alway sunshine and spades... Lake Tennyson completed installation GPS station installation near Seddon Clarence River install Temporary GPS installation

View Online Caroline Little 2016-11-30T01:11:24Z

Updated on the state of New Zealand volcanoes

Mon, 28/11/2016 - 16:03

Blog post added by Sara McBride

Monday 28 Nov 2016 

Our volcanologist-at-large, Brad Scott, updates us on what’s been going on with our volcanoes over the last couple of weeks. Post the Kaikoura earthquake we have maintained a close watch on the volcanoes. To date we have not seen any changes that can be directly related to the earthquake or the aftershock activity. We have seen changes, as we always do at the active volcanoes, but do not consider any are directly related to the Kaikoura event. However, we can’t eliminate the possibility that activity may change in relation to more shakes around the country.  

Volcano rundown: let’s start at the top

Photos from the recent trip to White Island Photos from the recent trip to White Island  

Starting offshore North of New Zealand, we work our way south along the Kermadecs, beginning with Monowai submarine volcano. There has been no activity noted since 11-12th November. However, we did notice a random pumice raft in the middle of the ocean near Tonga but this looks unrelated to Monowai.

Next is Raoul Island, nothing new is apparent there, only the Crater Lakes showing their usual summer warming cycle, due to the warmer weather.

A team visited White Island (Whakaari) and our ever watching Dino, last Thursday with a film crew and made several observations. The temperature of the main vent in the active crater has declined, down from 280 to around 140 °C. The small pools of water on the crater floor are getting smaller. The temperature of the hottest accessible fumarole (steam vent) remains around 180 °C. The gas flux has varied from around 300 to 600 tons per day of SO2. Overall the situation remains very similar at White Island (Whakaari) to how it was a couple of weeks ago.

Auckland Volcanic Field is also quiet too, no earthquakes near there. Moving south, Okataina Volcanic Centre (this includes Tarawera) is quiet, just a couple of small shallow earthquakes nearby.

The big news in volcano land this week is the that there has been a small steam (hydrothermal eruption) in Lake Rotorua. Eruptions have been known in this area all through our written history (1830 – present), so it’s not too unusual. The occurrence of steam eruptions has been variable in Rotorua, with many during the exploitation of the geothermal system, however they declined after the bore closure (1987). The last significant one was in 2001. We’ll be keeping a close eye on this latest hydrothermal eruption but, as this is pretty much business as usual for this system, we aren’t too concerned about it. We went down to check out the eruption and it didn't leave much interesting evidence

Our central volcanic zone is pretty quiet too. Taupo Volcanic Centre is quiet, just a couple of small earthquakes. Further south, the Tongariro-Ngauruhoe area is very quiet, again just a couple of small earthquakes. A team visited Te Maari and measure 308 °C from the vent here. The volcanic tremor at Ruapehu remains weak. The lake temperature is now 24.5 ˚C, continuing to slowly decline.

Mt. Taranaki continues its silent watch over the West Coast of the North Island.

So that ends our tour. And thankfully, it looks like the volcanoes have continued to ignore the Kaikoura earthquake sequence.

 

 

 

View Online Sara McBride 2016-11-28T03:03:14Z

Kekerengu Fault has a Word to its Geologists

Mon, 28/11/2016 - 13:41

Blog post edited by Caroline Little

New Zealand’s National Seismic Hazard Model (Stirling et al., 2012) clearly shows that the North Canterbury-Marlborough area affected by the M7.8 Kaikoura earthquake is expected to experience strong ground motions (yellow, orange, red, black colours) One of Tim and Russ’s trenches (pink rectangles) was cut in half by movement on the Kekerengu Fault (red line) in the M7.8 Kaikoura earthquake. The two sides of the trench are now about nine metres apart. Drone photo by Julian Thomson Rupture of the Kekerengu Fault can be seen especially clearly where it cuts across man-made features such as this farm track. Will Ries is measuring how far the road has been moved both horizontally and vertically across the fault. Photo by Tim Little The green “sausages” on this map show the current understanding of where surface fault rupture occurred in the M7.8 Kaikoura earthquake. Russ Van Dissen walking the Kekerengu Fault to observe the ground deformation that occurred in the Kaikoura earthquake. Photo by Kate Clark.

Written by Ursula Cochran

Last year Tim Little of Victoria University of Wellington and Russ Van Dissen of GNS Science thought it would be a good idea to find out more about the Kekerengu Fault in North Canterbury. Through previous work they had identified the Kekerengu Fault as likely to be the fastest slipping fault within 100 km of Wellington city apart from the Hikurangi subduction zone.  

They knew this meant it posed a significant seismic hazard to the northeastern South Island and also to Wellington if linking faults in Cook Strait ruptured at the same time as the Kekerengu Fault.

In February of this year, with funding from the Natural Hazards Research Platform, Tim and Russ excavated three trenches across the Kekerengu Fault to look for evidence of past large earthquakes. The main aim of their project was to better constrain the seismic hazard posed by this major active fault.

In these trenches Tim and Russ found evidence that at least three past large earthquakes had occurred in the last 1250 years. These initial results confirmed that the Kekerengu Fault was capable of producing large earthquakes frequently (on average, about every 300 or 400 hundred years), and was likely to do so again in future.

Then, two weeks ago, as if to say, “Don’t underestimate me!” the fault ruptured right through those same trenches. Tim was awe-struck. As a geologist working on active faults he said, “I had often wondered what it would look like if a fault moved while we were working on a trench cut across it, but I had never expected this to happen to me.”

When the Kekerengu Fault moved as part of the M7.8 Kaikoura earthquake the impacts on the landscape were dramatic. One side of the fault has moved as much as eleven metres with respect to the other side. Tim did not expect quite this amount of slip on this fault during a single earthquake. Russ, though, was less surprised – he says it fits with the long-term slip rate calculated for the fault – but he is still amazed to see such fault movement in action.

So, we knew about this fault, we knew it posed a seismic hazard, we even thought it was possible that it would rupture jointly with other faults – New Zealand’s National Seismic Hazard Model specifically includes scenarios that involve joint rupture of the Jordon, Kekerengu, and Needles Faults. And this, now confirmed by NIWA’s offshore survey of the Needles Fault, is exactly what happened on Monday 14th November. What we had not foreseen is that even more faults would be involved in a single earthquake sequence.

Currently we have evidence for seven faults rupturing in the M7.8 Kaikoura earthquake so work on the Kekerengu Fault is just a small part of the earthquake geology response. There are teams from University of Otago, University of Canterbury, University of Auckland, Victoria University, GNS Science, and NIWA, not to mention volunteers from overseas, currently mapping and measuring the faults that moved last week. We want to understand what happened in this event but, most importantly, what it means for future events.

The Kekerengu Fault has been speaking to geologists-in-the-making for generations because Victoria University’s third year structural field geology course is held near its northern end. I still clearly remember the Kekerengu Fault back in the early 1990s as a subtle, curious line in the landscape that our professor – Tim Little – stood astride inciting us to notice. Today, the fault has spoken and it is impossible not to notice.

View Online Caroline Little 2016-11-28T00:41:03Z

Updated: Gisborne and Hawke's Bay slow-slip event now extends to include Kapiti and Manawatu regions following M7.8 Kaikoura Quake

Sat, 26/11/2016 - 18:17

Blog post edited by Caroline Little

Update 6pm, Saturday 26th November:

The slow-slip event detected earlier this week of the east coast now has company. More slow-slip movement on the Hikurangi subduction zone (where the Pacific and Australian plates meet) has now been detected by GeoNet and PositioNZ cGPS sites in the Kapiti and Manawatu regions. We have recorded multiple slow-slip events in all of these regions previously (since they were first discovered in early 2002), and sometimes one region slips after another, however we have never detected slow-slip simultaneously in multiple regions. We have also never monitored slow-slip following a central New Zealand earthquake as big as the M7.8, so this could be typical bahaviour in the aftermath of such a large earthquake. We are continuing to monitor the event closely as it unfolds, and we will provide regular updates. The Kapiti-Manawatu slow-slip event has involved movement across the Hikurangi subduction zone plate boundary of between 5-7cm,  equivalent to a magnitude 6.8 earthquake in the last two weeks.  The Gisborne-Hawke’s Bay event has involved slip across the plate boundary up to about 15cm, equivalent to a magnitude 7.2 earthquake.  The cGPS data suggest that the Gisborne-Hawkes Bay slow slip event appears to be tapering off in the last day or two. 

Areas of slip - updated Saturday 26 November

GPS stations have detected a slow-slip event under the Hawke’s Bay and Gisborne regions in the days following the Kaikoura M7.8 Earthquake.

What is a slow slip event and how are they detected?

GeoNet, in partnership with LINZ run a network of GPS stations around the country that are able to detect land movement as little as a few millimeters resulting from silent earthquakes. These silent earthquakes or slow-slip events are undetectable by both humans and GeoNet's seismographs. They can move faults the equivalent of magnitude 6+ earthquakes over a period of weeks to months, without any detectable shaking.

These slow-slip events occur below the earth’s surface where the Pacific Plate meets the Australian Plate, along the Hikurangi Subduction Zone.
More info: on the GNS webpage and GeoNet Q&A about slow-slip events.

The slow-slip event following the Kaikoura Earthquake

The ongoing slow-slip event off the North Island’s east coast has moved some GPS stations up to 2-3 centimetres. This movement is similar to what has been observed in previous East Coast slow-slip events over the last 15 years, so is not necessarily abnormal. We see events in this area usually every 1-2 years. We have also observed other slow-slip events happening in response to large earthquakes. The last slow-slip event offshore of Gisborne followed the Te Araroa earthquake in September 2016 (related GeoNet story http://info.geonet.org.nz/x/ZIAvAQ). A slow-slip event also occurred following the 2007 M6.7 Gisborne earthquake.

This slow-slip event is particularly interesting as it appears to involve slip along the plate boundary from Hawke's Bay up to East Cape at the same time. Normally we see slow-slip events in these regions but they are separated in time or happen one after the other, as was the case after the Te Araroa Earthquake. It is possible that passing seismic waves from the M7.8 earthquake caused stress changes that triggered the slow slip event. GNS Science and GeoNet and scientists are keeping a close eye on the event as it evolves.

Map of GPS stations plotted in the graph to the right Modelled areas of movement beneath the seafloor. The model is derived from movement of land recorded on GPS instruments.

 

Porangahau Earthquakes

 

Earthquakes recorded in the Porangahau area since 14th November

Update: Saturday 26 November

As of Saturday 26th November, 225 earthquakes have been recorded in the Porangahau region since the Kaikoura Earthquake. Most of the earthquakes have been smaller than magnitude 3.

A magnitude 5.5 earthquake struck on 22nd November , 65 km south-east of Porangahau.

This is in the same area as the slow-slip event detected offshore of Hawke's Bay and Gisborne (see below).

Clusters of earthquakes, generally less than magnitude 5, have occurred multiple times in this area offshore of Porangahau, including 2001, 2006, and 2011. During the 2006 and 2011 cluster we also observed a slow-slip event in the same area (GeoNet started installing GPS instruments in the Hawke's Bay in 2002 so we don't know if the 2001 cluster was also associated with slow-slip event, though we suspect it might be).

Previous earthquake clusters in this area have gone on for weeks.

What does this mean?

Unfortunately, no one can give a definitive answer to this question as the precise linkage between slow-slip events and standard earthquakes is not well understood - this is still an area of active research. Like lots of scientific discoveries, these slow-slip events were stumbled upon while investigating something else entirely. They were first discovered in North America a few decades ago, and only discovered in New Zealand in the early 2000s when GeoNet and LINZ began installing GPS stations around the North Island.

Large earthquakes can happen any time in New Zealand, so it's essential to be prepared for them. Check out Civil Defence for advice on how to be prepared.

As always, we will update this story as the event evolves.

Contact scientist: Laura Wallace l.wallace@gns.cri.nz

View Online Caroline Little 2016-11-26T05:17:45Z