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It’s a valid question, and one we’ve been hearing a bit, but unfortunately we really don’t have the answer.

Following the Kaikoura Earthquake, slow-slip events have been observed simultaneously in the Gisborne, Hawke’s Bay, and now Kapiti regions. We’ve been observing slow-slip events in these regions (and Manawatu) for 15 years now, and we’ve never seen them happen in multiple locations all at once. But we’ve never tracked slow-slip events after a large magnitude 7.8 earthquake, so this could the normal pattern after such a large quake.

We’ve written a story last week explaining what slow-slip events are and what’s happening right now.

So what does all of this mean going forward?

Earthquake activity around Porangahau following the M7.8 Kaikoura earthquake and the slow-slip activity has increased uncertainty about the likelihood of subsequent earthquakes.

However, because the science of slow-slip events is still in its infancy, at this stage we’re not able to definitely assess, in terms of our forecasts, the changing risk caused by the slow-slip activity.

Currently our forecasts – based on statistical modelling – calculate that it is extremely unlikely (less than 1% in the next 30 days) that there will be another large earthquake (M7.8 or greater). We’re not changing our forecast numbers at this time due to the slow-slip activity.

The slow-slip events may mean there is an increased risk of a large earthquake (M7.8 or greater) in the lower North Island. Were such a quake to occur it would be likely to cause a large tsunami that would pose a threat to coastal communities in much of the North Island, the Upper South Island, and Chatham Islands.

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, all the time) is that now is the time to be proactive and make sure that you’re prepared for an earthquake and tsunami. We know that being prepared makes a real difference in helping you respond to an event, and in helping you recover afterward.

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.

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.

23/11/2016 4.45 p.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 forecasted. 

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 forecasted, but the numbers are still within the forecasted 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 Wednesday 23 November we had detected 4879 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 (4828 earthquakes <M4.9) and would have only been felt close to the epicentre. As of Monday 21st, there were also 47 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 pebbles to go unnoticed, but pebbles are still being skipped on the lake. 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 4879 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

Total number of aftershocks by noon, 22 Nov

 

44

 

3

 

0

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 the lower end of our forecasted range.  The table above shows the range in the number of aftershocks that we have forecasted for 24-hour time intervals, compared to the number of earthquakes that we have actually detected so far, for three magnitude ranges.  

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 forecasted.

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.

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 forecasted 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 updated for the longer term forecast or may be changed as required). 

 

The GeoNet network of seismometers and continuously operating GPS instruments have allowed an unprecedented view of the propagation of the M7.8 Kaikoura earthquake in real time.  Computer simulations using GeoNet seismological data allow us to watch the progress of the rupture as it punched its way up the east coast of the South Island over an approximately two minute period early in the morning of November 14th

Because Geonet’s seismic network had numerous seismic stations situated very close to the rupture (just like its Canterbury Seismic Network during the 2010-2011 earthquake sequence), the data from these sensors allow us to essentially travel back in time and watch the event unfold.  Computer simulations of the seismological data (using two very different methods—see figures below) suggest that the rupture started in the south, on a fault at approximately 15 km depth near Culverden. The initial rupture near Culverden subsequently triggered a domino effect, as the earthquake rupture jumped from fault to fault, essentially “unzipping” along a 150 km length of the northeast coast of the South Island.  The data suggests that many faults were involved in the rupture. 

Chronological evolution of the fault rupture as the earthquake progresses. Colour scale in metres of slip.

Data (seismograms) show the vertical acceleration at GeoNet strong motion stations. 

Movie showing migration of maximum energy released during the earthquake.

Coloured circles represent progression with time (in seconds following the main shock) of the energy release.

 

The earthquake rupture picked up a head of steam as it passed Kaikoura, with the largest fault movements occurring between Kekerengu and Cape Campbell.  This pattern is confirmed by GPS and satellite radar observations. Near the end of the earthquake’s runaway journey, it jumped onto a series of faults offshore. NIWA has found clear evidence of large earthquake displacement on one of these--the Needles fault (NIWA story).  The earthquake rupture terminated abruptly just before reaching Cook Strait.  There is no evidence at this time that the Hikurangi subduction zone was significantly involved in the rupture.

The Kaikoura M7.8 earthquake is arguably the most complex earthquake rupture ever to be observed in this level of detail with modern instrumentation (seismic sensors, GPS instruments, and satellite radar data).  Multiple datasets (seismology, geodesy, and surface observations of faulting, uplift, and tsunami) are rapidly converging to give us a single, consistent view of exactly what happened in the earthquake. Preliminary models, will of course be refined, as new information continues to come in.

Science contacts: Caroline Holden and Bill Fry, GNS Science

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. 

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.

 

Porangahau Earthquakes

 

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

Monday morning’s M7.8 earthquake near Kaikoura has caused massive permanent displacement of the land in the northern half of the South Island (GeoNet Story on Coastal Uplift). Detailed knowledge of these land displacements provide us with critical clues to help determine which faults ruptured during the earthquake, and how much movement occurred on them. Although many GNS and GeoNet scientists are currently “on the ground” trying to obtain information about the earthquakes and its impacts, sometimes we can get an even better picture of what happened in the earthquake by stepping back and viewing it from space. 

To do this, we must turn to specialized satellites that collect radar data that can be used to track these land movements in great detail. A technique called InSAR, which stands for ‘Interferometric Synthetic Aperture Radar’, utilises radar satellites orbiting ~700 km above the earth to precisely measure the distance between the ground and the satellite. If the ground moves between two subsequent satellite passes, due to an earthquake or volcanic eruption, then the distance between the ground and the satellite changes. Observing these changes in the positon of the land with InSAR enables us to generate detailed maps of ground movement, often with centimeter-level accuracy.

The InSAR images that have been coming out from the European and Japanese satellites are astonishing, and give us the most detailed view yet of what happened in the M 7.8 quake.  The satellite images reveal huge changes in land movement across the Hope and Kekerengu faults, as well as several other faults in the region.  To the east of these faults, the land went mostly southwest (see blue area in the figure on the left). In contrast, to the west of these faults the land moved mostly northeastwards (see red area in figure on left). Sharp changes in land movement are visible on the InSAR images, and show us where the faults ruptured to the Earth’s surface.

The satellite images clearly show that Monday’s M7.8 earthquake is one of the most complex earthquakes that has ever been observed. Consistent with observations from geologists of fault displacements on the ground, the InSAR results suggest that the earthquake ruptured at least four different faults, and probably more. The biggest displacements are seen on the Kekerengu, Hope, Hundalee, and Papatea faults.

Scientists at GNS have done computer simulations to replicate the ground displacements observed by the satellites and GPS measurements (GeoNet Story on GPS). To fit the InSAR and GPS displacement data, the computer simulations require up to 10 metres of slip across the Kekerengu fault north of Kaikoura. Our scientists are working hard to pull all of the details that they can out of these exciting and important satellite images to better inform our understanding of what happened in the massive quake.

 

 

A perspective 3-D view towards the east coast of the South Island of the results from the computer simulation to determine the amount of movement on faults in the earthquake.  The model shown fits the InSAR and GPS displacements well. The faults are shown as a mesh of rectangles. The colors show the amount of slip on the faults in the model (in meters).  Some portions of the faults (representing the Kekerengu fault) accommodated up to 10 metres of slip

 

Contact Scientist: Ian Hamling, i.hamling@gns.cri.nz


After the Kaikoura Earthquake, the GNS landslide and paleoseismology teams were quick to take to the air on the 14th November to find evidence of the earthquake effects in the landscape. The team were fascinated by the sights they saw from the helicopter. The effects were widespread over an area of 7,000 km2 with estimates that there has been between 80,000 to 100,000 landslides triggered by the earthquake and subsequent aftershocks.

Along the coastline damage became apparent south from Cape Campbell, becoming more intense south of the Clarence River, with several large (100,000 – 500,000 m3) landslides disrupting both SH1 and SIMT 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 SH1 and SIMT. 

Landslide Dams

Since Tuesday, GNS has been working to compile a complete inventory of landslide dams in the area affected by landslides after the earthquake. This work has two parts. The first involves using remotely sensed imagery to locate landslide dammed lakes in inland areas. The second involves a systematic search of vulnerable areas. 

A satellite image from WorldView-2 image was received and processed. This image covers part of the area north of Kaikoura and has identified 12 landslide dams. Only one was known prior to processing this image.

GNS has also started systematically flying landslide affected areas to visually identify landslide dammed lakes. The southeast flank of the Seaward Kaikouras, was flown on the 16th November and seven landslide dams were found. These flights will continue over the next three or four days. The purpose of these flights is to systematically cover affected areas where no data is currently available. The second purpose is to photograph the landslide dams to allow assessment of the hazard at each site.

As the data comes in it is being forwarded to NIWA to undertake dam-break modelling, which will help determine what will happen if the dam-breaks. From this people and assets at risk can be identified.  

 

Safety around Landslides

Please take precautions and stay away from regions of landslides and landslide dams. Avoid rivers or streams that have been blocked by landslides. Stay away from steep cliffs and slopes in the Kaikoura and Marlborough region. 

Director of the Ministry of Civil Defence and Emergency Management, Sarah Stuart-Black, advises that people in those areas to be especially vigilant and to keep clear of river valleys and outlets. Landslide dams can break quickly, and release large volumes of water and sediment as a flood wave. Homes at potential risk have been advised to evacuate.

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

 

GeoNet, with funding from LINZ (Land Information New Zealand), operates a large network of continuously recording GPS sites in New Zealand to track land movements on a daily basis.  Within a couple of hours of the M7.8 earthquake, GeoNet was able to use the GPS data to estimate the initial displacements of the Earth’s surface that occurred during the earthquake.  Tracking these types of land movements as the result earthquakes is a critical piece of the puzzle needed to determine which faults ruptured, and by how much.

Shifting of the land near the earthquake

 

 

What the GPS revealed was astonishing. It turns out that the earthquake shifted the land at Cape Campbell (the northeast tip of the South Island) to the north-northeast by more than 2 m, and up vertically by almost 1 m. This means that Cape Campbell is now more than 2 m closer to the North Island than it was before the earthquake. Similarly, Kaikoura has moved to the northeast by nearly a metre, and has been lifted upwards by 70 cm. Hanmer Springs, which was our closest GPS site to the quake epicentre, jumped eastward by approximately 50 cm. All of this movement happened during the earthquake in a matter of seconds.
Movements of the Earth’s surface near the earthquake recorded from GPS have been incredibly important to help diagnose what motions were involved in the earthquake. A key observation is that although the earthquake fault rupture began near Culverden, by far the largest motions of GPS sites occurred at Cape Campbell. This supports the idea that the ruptured north over a very long distance from where it started.

A lot of New Zealand has moved

 

Not only did the earthquake shift landmasses in the northern South Island, but it also caused movements across most of the country.  In the lower North Island, the east coast has shifted west by 1-5 cm, while the Wellington and Kapiti regions were shunted 2-6 cm to the north. Christchurch and Banks Peninsula didn’t miss out on the action, either—they are now approximately 2 cm further south than they were the day before the quake. Some parts of the west coast of the South Island have been shifted eastward by as much as 10 cm. The northern North Island and southern South Island only moved a few millimeters.

 

Updated 1pm, 21/11/2016

UPDATE Monday 21st November

Over the weekend we conducted further reconnaissance trips via helicopter to refine how the Kaikoura Earthquake uplifted areas of the East Coast of the upper South Island. This is a map of preliminary coastal uplift measurements along the Kaikoura coastline from the Conway River to Cape Campbell. We have compiled three sets of uplift observations for this map. The most accurate information is from the tide gauge (green dot), but we only have one tide gauge in the area, located at Kaikoura. The measured points (red dots) show locations where GNS Science and University of Canterbury teams surveyed the coastal uplift. Biological markers of pre-earthquake tide levels were surveyed relative to the post-earthquake tide levels. The range in values reflects the elevation range of the biological markers and the uncertainty in surveying methods and the tidal correction. The helicopter points (blue dots) represent areas where we estimated the amount of uplift from our helicopter observations during high tide and low tide survey flights, these have the largest amount of uncertainty. Survey teams will revisit the area again this week to increase the density of our observations.

Our preliminary insights from this work is that coastal uplift is highly variable along the Kaikoura coastline. The startling uplift of ~5.5 m at Waipapa Bay is a localised block pushed up between two traces of the Papatea Fault and is thankfully not representative of the whole coastline. The surveys teams would like to thank the residents of the Kaikoura coastline who have been so welcoming to scientists, hearing the resident’s observations of the coastline and the impact of the earthquake has been hugely valuable and we hope that our post-earthquake science survey can contribute to our knowledge base of these very rare, but hugely impactful events.

Much of the northeastern coast of the South Island was uplifted during the 14th of November 2016 earthquake. We know this from photos of rock platforms covered in seaweed and marine animals such as crayfish and paua stranded above tide levels. Our records measured the tide gauge at Kaikoura was lifted up by 1 m, and continuous GPS monitoring sites at Kaikoura and Cape Campbell were also raised by 0.7-0.9 m. At this stage we can estimate that the coast was raised between 0.5 m and 2 m from about 20 km south of Kaikoura all the way north to Cape Campbell. Scientists plan to find out more about this coastal uplift.

What is coastal uplift?

Coastal uplift is when the land is raised above the sea by tectonic forces. It can happen gradually over geological timescales or suddenly by an earthquake.

How does it happen?

Sudden coastal uplift happens as the result of large earthquakes. Vertical movement on a fault can cause land to be pushed up. This is the type of movement that has built many of the mountain ranges in New Zealand. When such vertical movement on a fault happens near the coast, land is raised above sea level. Sea level is a powerful horizontal marker for measuring tectonic movement because it is very obvious which land used to be under water before the earthquake!

 

 

Is coast uplift normal?

Coastal uplift is normal for large earthquakes near the coast that include some vertical movement on a fault. Most movement on the faults that ruptured in the Kaikoura M7.8 earthquake was horizontal, but there was some vertical movement too, so it is not surprising that there has been some coastal uplift from this event.

In New Zealand there is evidence preserved in the landscape that shows many parts of the coast have been repeatedly uplifted through time. For example, raised marine beaches and terraces along the Kaikoura Peninsula, Wairarapa coast, Cape Kidnappers, Mahia Peninsula, north of Gisborne and East Cape, are evidence of former beaches that were uplifted from the sea by earthquakes in prehistorical times. Many of these have been or are currently being studied to find out the size and age of past earthquakes.

 

 

Historical examples

In historical times we have had several examples of earthquakes causing coastal uplift that, although devastating in the short term, have led to some benefits. For example, in 1931 the M7.8 Hawkes Bay earthquake raised land around Napier by 1-2 m above sea level. Land that used to be estuary now provides space for Napier airport. In 1855 the M8.2 Wairarapa earthquake raised much of Wellington by 1-2 m. The road from Wellington city to the Hutt Valley became viable as a result of the new land around the harbour’s edge.

Will the land go back down?

Probably not. The newly raised coastline of the Kaikoura coast is most likely a permanent feature. Historical and pre-historical examples show that in many parts of New Zealand these raised beaches remain high above sea level. However, in some parts of the world, raised beaches have been known to gradually drop down again (over centuries) or be dropped down suddenly in a large earthquake with a different sense of movement.

What will happen to all the sea creatures?

There will be a major shift in the community of marine species. Many seaweeds and animals that would normally be permanently covered by water will now be struggling to exist in a zone of transition between air and sea. Some of the animals that have been raised will be accustomed to air exposure for short periods of time, but not the full tidal cycle that they will now experience. As the animals not suited to this environment die from the reef, they will be replaced by seaweed and animals appropriate for the new tidal level. 

What are scientists doing to study the coastal uplift and its impact? 

There are several studies being planned by geologists and biologists. Over the next weeks and months geologists will be undertaking surveys along the coastline to measure the amount and extent of coastal uplift that has occurred. Recording this information will help us to understand which faults ruptured in the earthquake, and how much slip occurred on those faults. Over the coming weeks marine ecologists and fisheries scientists will be surveying areas on the rocky shore to understand the sequence of change. The surveying will continue for in the long-term for changes to be captured.

The information collected by scientists will be publicly available.

Can the public contribute their photos and observations?

YES! The coastal uplift covers a long stretch of coastline and the scientists will not visit every location. We are interested in photographs of: 

  • displaced coastal features such as the uplifted reefs and rock platforms;
  • displaced marine life especially before and after photos if animals are being rescued and removed from the reefs;
  • uplifted man-made structures such as jettys and boat ramps particularly if they have tide level markers on them.

We are also interested in people’s observations, particularly residents who have familiarity with the coastline pre- and post-earthquake. To be of most use, we would like to know the location, date, time of the photograph and if possible, context and scale.

As always your safety comes first, please do not put yourself at risk to collect this information.

Photographs and information can be sent to: k.clark@gns.cri.nz

Citation for map: Clark KJ, Goldstein S, Villamor P, Berryman KR, Gerrity S. 2016. Preliminary coseismic coastal uplift measurements from the 2016 M7.8 Kaikoura earthquake. GNS Science. http://dx.doi.org/10.21420/G2H59W

Maps updated with additional station data 11am,  

I think we can all agree there has been a lot of shaking over the past few days. Scientists from GNS Science and University of Auckland, GeoNet field technicians and our platform team, have been busy at work collating the data to figure out exactly how much shaking occurred. While we still haven't retrieved all of data, here is what we have so far.

Ground shaking caused by the Kaikoura Earthquake reached over MMI VIII near the fault rupture, on the Modified Mercalli Intensity Scale and is considered severe. In Wellington, some areas experienced shaking up to MMI VI-VII, which is considered strong. This is based on the current Shakemap calculation, which includes both measured data and estimated values. This may be updated as more information is acquired.

PGA Information

The strongest ground shaking measured by GeoNet instrumentation so far was a peak ground acceleration of (PGA) 1.3g in Ward. Since publishing this story, data has come in from the WTMC station in Waiau with a vertical PGA over 3g. As yet, we're unsure if this is a reliable value, it may have been contaminated by other effects.

 

 

The highest ground accelerations extend in a band trending northeast from the epicentre. This aligns with where the largest fault movements have occurred, based on field surveys.

In the Wellington region, PGAs exceeded 0.2g in parts of the CBD and Lower Hutt. This is similar to that experienced during the Cook Strait sequence (earthquakes of M6.6), however the duration of shaking was significantly longer (around four times) and there was more long period energy.

In Christchurch, the recorded PGAs were lower (less than 0.1g) even though the city is closer to the epicentre. This is related to the fault rupturing from the epicentre northwards away from Christchurch. This is our understanding based on what we know so far about the faults.

We are still acquiring strong motion data from the closest stations to the rupture.

 

 

Shakemap

Shakemap is a combined model of the estimated ground shaking based on instrumental observations from GeoNet sites and ground motion predictions based on the current fault models. As we get more information from InSAR (Interferometric Synthetic Aperture Radar) the fault models are likely to be updated.

Shakemap also takes into account soil conditions that can amplify shaking in certain areas. This can be seen on the map as areas experiencing higher shaking despite being further from fault rupture.

 

Before the foul weather set in, a team of GNS Science geologists, Nicola Litchfield and Pilar Villamor, went out on helicopter flights trying to pin down exactly which fault lines ruptured in the Kaikoura Earthquake.  Their observations confirmed what our seismologists have been saying – that this was a very complex earthquake. On their trip they observed several different faults rupturing the land. They mostly followed State Highway 1 as we flew down the east coast of the upper South Island. Roads are very useful markers for telling how much a fault has moved.
 

The trip in their own words:

 

Kekerengu and Waipapa Bay

“The first fault rupture we saw was the Kekerengu Fault. The fault shifted State Highway 1 and the railway line by at least 2.3 m horizontally and 1 m vertically. We followed the fault rupture from the beach inland for 2km to Bluff Station. Here, the earthquake had dislocated hills, fences, roads, buildings and the river bed, some by as much as 10m horizontally. A house was also spectacularly moved off its foundations - the occupants were shaken up, but otherwise okay. This was as far as we flew along this fault so the surface rupture could well have continued past this point.

We continued flying south. At Waipapa Bay the road and railway line were shifted by 1m. Further south, we came to the Hope Fault. From the air it looked like this has offset the road by about 1m. We didn’t follow the Hope Fault inland on this flight, but we’ve heard from other scientists who did fly along here earlier, that they didn’t see any disturbance of the land

 

 

Hundalee, Emu Plains, and The Humps fault zone (yes, someone long ago named a fault 'The Humps')

Then it was on to the Hundalee Fault. Again, we saw the fault had disturbed State Highway 1 and the railway line as well as the beach south of Kaikoura.

We then flew to the epicentre area (The Humps fault zone and Emu Plains) and found some fault ruptures on the north side of the Waiau River, some on previously unknown faults. It was less clear exactly how these faults had moved compared to the others further north, but it looked like some horizontal movement had occurred. At the western end these ruptures had affected some small streams.”

Field trips like this one can only find where fault lines have broken through to the surface. It’s likely that other faults below the surface (or longer lengths of the faults mentioned above) have also moved. Other investigations including satellite images will help to show any subsurface fault movements.

What Next?

Now that the wind and rain have subsided, additional teams are out in the field - they’re hoping to cover areas that Nicola and Pilar didn’t get to.


Fault Map by: Litchfield NJ, Barrell DJA, Begg JG, Benson A, Berryman KR, Clark KJ, Cochran UA, Cox SC, Gasston C, Glassey, PJ, Heron DW, Howarth JD, Langridge RM, Little T, Lukovic B, Nicol A, Pettinga J, Ries WF, Rowland J, Stirling MW, Townsend DB, Upton P, Van Dissen RJ, Villamor, P. 2016. 14th November 2016 Kaikoura Earthquake. Preliminary earthquake geology observations. GNS Science. http:dx.doi.org/10.21420/G2MW2D

Update , 13.30

The Kaikoura earthquake on Monday 14th November was the largest recorded in New Zealand since the M7.8 Dusky Sound earthquake in 2009. But, given its location, it was more widely felt and more damaging. This earthquake unsettled many, many people and that is perfectly normal; earthquakes can be upsetting events. The best advice we have is to be prepared for earthquakes.

Future aftershocks

More earthquakes will occur in future as part of the Kaikoura earthquake sequence.   We understand that aftershocks can be upsetting for some people.  These feelings are completely normal. Seek support with friends and family, and if you need additional support please see the information at the bottom of this page.  

To help understand the earthquakes and what to do about them, many people what to know what will happen next? While we can’t predict earthquakes we can provide some forecasts of future aftershocks and possible scenarios.

Probabilities have been calculated and scenarios have been developed and presented over the past few days.  With our current information the most likely scenario (Scenario One: Extremely likely: >92% probability within the next 30 days) is that aftershocks will continue to decrease in frequency over time.  We describe this scenario below, after some specific information about Wellington and Christchurch, along with two other scenarios that have much lower probabilities of occurring alongside Scenario One.

Wellington and Christchurch 

Aftershocks of Monday's M7.8 main shock are occurring throughout a broad area that surrounds the faults that ruptured in that earthquake. Most of these aftershocks are occurring near these faults, but a small number of aftershocks have occurred as far away as the lower North Island. Our current forecasts indicate that it is likely for that aftershocks near these faults will continue, but for the frequency of aftershocks to decrease with time.  We are already seeing this happen.

These maps show the distribution, based on our forecasts, of the probabilities of damaging shaking within the aftershock region, which includes Wellington. The area nearest the faults has a probability of 80% or more for damaging shaking in the next 30 days. In comparison, the probability of damaging shaking in the Wellington area (the darker blue tones) is less than 10%.  While this probability is considerably lower than in other regions, it is possible for shaking similar to what occurred on Monday to happen again in Wellington.  The forecast is for the next 30 days. Be aware that Wellington is already a high seismic risk area and Monday's earthquake has increased this risk, as illustrated in the forecasts. 

Christchurch's aftershock probabilities are not greatly affected by the M7.8 Earthquake.  The most recent update of the Christchurch aftershock probabilities are here. We update the Christchurch aftershock probabilities annually, due to the relative stability of the aftershock decay.

 

General information about the probabilities and scenarios

Most earthquake aftershock sequences decay over time, with spikes of activity and occasional larger earthquakes. Today's revised probabilities have decreased since the previous calculations. We use probabilities as we cannot predict earthquakes. The probabilities in the table below describe the likely progression of the sequence within the next day, week and month. The scenarios specifically address what we expect within the next 30 days, however, we expect aftershocks to continue for months to years.

Within this sequence, aftershocks will most likely occur anywhere in the box on the map (see image). It is this geographical region for which the modelling is done. It is important to understand that earthquakes can and do happen outside this box but the box represents the most likely area related to this sequence.

 

 

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 7 days

4.1

0 - 11

94%

0.38

0 - 2

32%

0.04

0 - 1

4%

within 30 days

12.2

4 - 23

>99%

1.2

0 - 4

69%

0.12

0 - 1

11%

within 1 year

40.6

24 - 60>99%3.61 - 898%0.350 - 230%

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, Monday, 5 December. * 95% confidence bounds.

For example, there is a 32% chance (down from 38% on 30 November) of one or more M6.0-6.9 earthquakes occurring within the next week. We estimate there will be between 0 and 2 earthquakes in this magnitude range within the next week. The current rate of magnitude 6 and above for the next month is about 45 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.

The next forecast will be issued around midday on Monday 5th December, unless there is a large aftershock that reinvigorates the sequence.

Scenarios

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: Extremely likely (>99% within the next 30 days)

The most likely scenario is that aftershocks will continue to decrease in frequency (and in line with forecasts) over the next 30 days. Felt aftershocks (e.g. over M5) would occur in the area from North Canterbury to Cape Palliser/Wellington. This includes the potential for aftershocks of between 6.0 and 6.9 (77% within the next 30 days). Scenario one will continue to play out, even if either scenario two or three also occurs.

Scenario Two:  Unlikely (approximately 20% within the next 30 days)

An earthquake smaller than the mainshock and between M7.0 to M7.8 would occur. There are numerous mapped faults in the North Canterbury, Marlborough and Cook Strait 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 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 M7.3 aftershock occurred approximately 2 weeks after the initial M7.8 earthquake.

Scenario Three:  Extremely unlikely (<1% within the next 30 days)

A much less likely scenario than the previous two scenarios is that recent earthquake activity will trigger an earthquake larger than the M7.8 mainshock. This includes the possibility for an earthquake of greater than M8.0, 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 M7.8 earthquake. 

Aftershock shaking forecasts

The maps presented here forecast the intensity of shaking from aftershocks (for the next 30 days from 5 December 2016) for shaking intensity MM7. This is represented by the Modified Mercalli Intensity (MMI) scale which is a different measurement to Magnitude. The MMI scale focuses on the intensity and impacts of the shaking. MM7 shaking is described as: “General alarm. People experience difficulty standing. Furniture and appliances are shifted. Substantial damage to fragile or unsecured objects. A few weak buildings are damaged.” It can also generate liquefaction.  In reading the maps you could say the probability of MM7 shaking (in the next 30 days) around the wider Kaikoura/northern East Coast of the South Island (reflected by the red colour) is over 60%.  In comparison, the probability of MM7 shaking in the Wellington region (the darker blue tones) is less than 10%. 

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

Other hazards

The earthquake activity has caused tsunami and landslides.  As a reminder, if an earthquake is too strong to stand up in, or lasts longer than a minute, move inland or to a higher point immediately; don’t wait for a siren or further information.

Extensive landslides have occurred as a result of the earthquake, and these remain dangerous. Material can move at any time. Please exercise caution when in the vicinity of landslides and cracks in the ground on slopes. If it is raining, the threat rises as the water can remobilise the landslide material as debris flows and debris floods (flash floods).  Landslides have also dammed rivers, which can breach, particularly after rainfall. Please avoid landslides in wet weather, and rivers downstream of dams.

Take care of yourselves and others – physically and mentally

Earthquakes can be very upsetting. Our scientists have also been pretty shaken up and have felt many aftershocks.

Please follow our friends at the Ministry of Civil Defence & Emergency Management on Twitter and Facebook for the latest in preparedness and tsunami information. Also, keep updated with your local and regional Civil Defence and Emergency Management Groups.

Beyond physical preparedness is the emotional and psychological support for these earthquakes. There is nothing wrong with being upset about the earthquake, it is a perfectly normal feeling. 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.

Further, two lives were lost due to this earthquake. Our thoughts go out to the family and friends of those people.

Updating you regularly

We will be updating as regularly as we can about this evolving situation.

A sustained but small swarm of earthquakes has occurred in Ngakuru Valley south of Rotorua in the Bay of Plenty over the last 36-38 hours. The most active part of the swarm lasted about 4 hours overnight 29-30 October.  We have recorded 132 earthquakes that are large enough to get locations in the last week. The earthquakes range from Magnitude 1.0 to Magnitude 2.9, while the depths ranged between 3 and 9 kilometres. The majority of these earthquakes are about five kilometres deep. Small shallow earthquakes like these will be well felt by local residents. We have received many felt reports from the area.

This swarm is typical of the earthquake activity in the greater Ngakuru-Waikite area south of Rotorua. The distribution of earthquake size is often variable during a swarm, in the case of this one the three larger events are spread through the sequence. One near is near the start, the second about 4 hours later and the largest (M 2.9) about 30 hours after the start. The Ngakuru area is in the centre of the Taupo Fault Belt, a zone of faulting between Rotorua and Taupo. The area is one of crustal extension, where the Taupo Volcanic Zone is getting wider.  Hence earthquake activity in this area is common been related to the faulting, not volcanoes or geothermal activity. They often occur as swarms. 

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. Forty of the earthquakes in this swarm are between M 1.5 and 2.0, while another 36 are between M 2.0 and 2.4. The largest is M 2.9 and occurred near the end of the activity. Some earthquakes are so small we can’t locate them with our equipment.  

Many local residents have reported feeling these earthquakes. These earthquakes are too small to be widely felt or cause any significant damage.  The Ngakuru area is about 17 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, but that lies 7 km east of Ngakuru. Many earthquakes occur in this area. GeoNet continues to monitor all activity throughout the Taupo Volcanic Zone.

 

 

Scientists here at GNS Science are still trying to unravel the details of the East Cape M7.1 earthquake. To add to this mix, both before and after this month's East Cape earthquake, there have been multiple silent earthquakes (also called slow-slip events) offshore from East Cape and the Mahia peninsula.

The recent spate of silent earthquake activity started at the end of August, around a week before the magnitude 7.1 earthquake. A silent earthquake was picked up on a few of GeoNet's GPS stations off the coast of Anaura Bay (area 1 on the map). It looked as though it was tapering off when the magnitude 7.1 quake struck, kicking the silent earthquake back into life and extended the area of movement further to the north (area 2 on the map). Judging by previous silent earthquakes in the area, this current one has moved the equivalent of a magnitude 6.5 earthquake. In the last few days, while this silent earthquake is coming to an end, another one is starting up offshore of Mahia peninsula (silent earthquakes happen so gradually it's tricky to pick exactly when they start and finish).


Auto-updating graph showing two years of movement at two of GeoNet's GPS stations at Anaura Bay and Mahia Penninsula.
The big jumps up are the silent earthquakes.

How do silent earthquakes relate to traditional earthquakes?

How traditional earthquakes and silent earthquakes interact is still a relatively new area of study - there have been many examples of small earthquake swarms associated with silent earthquakes, as well as a few examples of larger quakes and silent quakes happening around the same time. The Gisborne M6.7 earthquake in December 2007 triggered a silent earthquake. With silent quakes happening about once a year off the East Coast of the North Island, they are much more frequent than large earthquakes.

This area of New Zealand is very interesting to other scientists around the world, Japan's Kyoto University currently have sensors on the ocean bottom offshore of Gisborne. Researchers hope that these instruments will build a more complete picture of what happened in both the East Cape M7.1 quake, as well as these silent quakes. Unfortunately scientists are in for a long wait, as these instruments aren't due to be collected until mid-2017.

What are silent earthquakes?

Silent earthquakes are undetectable by both humans and GeoNet's seismographs but they can move faults the equivalent of magnitude 5+ earthquakes. A normal earthquake is over in less than a minute, but these East Coast silent earthquakes take anywhere from a week to a month to unfold. We can detect silent earthquakes only with GPS stations, which track land movement. The East Coast of the North Island is slowly pushed west. When a silent quake occurs, the land jumps back towards the east. Silent earthquakes happen at many of the subduction zones around the world - where one tectonic plate dives beneath another.

Want more info?

Have a look at the Science Learning website's animation of silent earthquakes

Listen to a podcast interview of one of GNS's awesome research scientists Laura Wallace talk about everything slow-slip related.

A small swarm of earthquakes has occurred near Kawerau in the Bay of Plenty over the last 24 hours. The busy part of the swarm lasted about 18 hours over night 19-20 September.  We have recorded 20 earthquakes that are large enough to get locations in the last week. The earthquakes range from Magnitude 1.8 to Magnitude 3.1, while the depths ranged between 2 and 10 kilometres. The majority of these earthquakes are about five to six kilometres deep. Small shallow earthquakes like these will be well felt by local residents.

This swarm is typical of the earthquake activity near Kawerau. Earthquake activity in this area often occurs as a swarm which is very typical of earthquake activity in the Taupo Volcanic Zone, where 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. Sixteen of the earthquakes in this swarm are between M 1.8 and 2.2, while the other 4 are larger. The largest is M 3.1 and occurred near the middle of the activity. Some earthquakes are so small we can’t locate them with our equipment.  

Many local residents have reported feeling these earthquakes. These earthquakes are too small to be widely felt or cause any significant damage.  The Kawerau area is about 25 km from Whakatane and is characterised by many active faults and a large geothermal system. GNS Science geologists have mapped numerous active faults in the area. The most famous is the Edgecumbe Fault which moved in March 1987. Many earthquakes occur in this area. GeoNet continues to monitor all activity throughout the Taupo Volcanic Zone.



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

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