Natural Hazards

Christchurch Quake Q&As

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Kelvin Berryman (Image: Stuff.co.nz) The following questions were posted by a Christchurch resident on our GNS Science Facebook page. I think they are good questions which will be of interest to many people in the quake affected area.  I have re- posted them here, along with answers provided by Kelvin Berryman, a leading earthquake scientist at GNS Science, and manager of the Natural Hazards Research Platform. Kelvin was awarded the Queen’s Service Order in the 2011 Queen’s Birthday Honours recently for his services to science.  Request on behalf of everyone who lives in Christchurch, we are all so afraid and re-thinking our futures – it would be good if some questions could be answered in plain English for us: 1. Are you aware of ALL the major fault lines in Canterbury – Yes I think the research community knows where the MAJOR faults are. However, the current Canterbury earthquakes are being generated by some quite moderate-sized faults – they are buried beneath many 100’s of metres of gravels or the several million year old volcanic rocks of Banks Pensinsula. We cannot see all of this size of fault. Liquefaction volcanoes dot the beach, June 2011  2. Which faults are the biggest risk for large earthquakes? The faults that are being strained the hardest have the highest chance of producing large earthquakes. In the South Island these are the Alpine, Hope (through Hanmer to Kaikoura), Porters Pass (look to the right the next time you drive over Porter’s Pass toward the West Coast to see the fault line crossing the hillsides), and further north into Marlborough. Unfortunately all faults that are being strained have to break some time, and this is what is happening around Christchurch at present. These are very rare events for Canterbury, although I realise completely this scientific understanding provides no solace for the people who have lost so much.  Ready to topple… Port Hills boulder 3. What are the future implications, area by area e.g. which are the safest areas to live in? In Canterbury the safest areas are probably those farthest from current earthquake activity, and to the west away from the liquefaction susceptible areas are better. In New Zealand areas north and west of New Plymouth and Hamilton have a lot fewer earthquakes than other parts of the country. But remember that other natural hazards like floods, and tsunami have different likelihoods in different parts of New Zealand. 4. What % risk is there of a tsunami – I do understand that there are many faults on our coast line, how sure are you that there is no tsunami risk, vertical or horizontal, and why?  Rockfall at Redcliffs RSA Canterbury does have a risk of tsunami but the principal source is huge earthquakes occurring in South America, and it takes roughly 12 hours for the tsunami to arrive, so there is plenty of time to be safe. The fault lines offshore of Canterbury are small and not capable of producing a major tsunami, but if you are on the beach when you feel a big earthquake and the shaking goes on for 20 seconds or more then it is important to get several metres above the beach. Go quickly walking, perhaps drive if practical, but watch out for being stuck in a traffic jam at low elevation when simply walking or running for 50-100m is all you need to do. If you live near the coast join a local group, obtain readily available information on self evacuation planning, and make a community plan. The local civil defence officer will help you.  Extreme Shaking 5. Are you – (scientists/geologists in Christchurch) afraid when an aftershock hits, if you shared exactly your feelings thoughts on this issue it could give us all some peace on the subject. To be honest I think the residents of Canterbury have now have more experience of earthquakes than most earthquake scientists.  I think most people whether they are scientists or not are apprehensive when an earthquake starts and will often be afraid too. Perhaps we have the advantage of trying to remember our scientific training when in those few seconds we are thinking about how big will it be. I am sure now that with your experience you know that the really big and damaging earthquakes hit so hard that you are thrown down or find it difficult to move. Fortunately these ones are much less common than the smaller but nevertheless worrying ones.                                 ~          ~          ~          ~ For more geoscientist’s answers about the Christchurch Earthquakes, have a look at the ‘Ask an Expert’ page published earlier this week in the Christchurch Press.

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Rockfall impacts from the Christchurch ‘Quake

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Today I have been in the Port Hills of Christchurch with Chris Massey, an engineering geologist in the GNS Science Active Landscapes team. Chris is part of a team undertaking a detailed study of the rockfalls that have been triggered in and around Christchurch as a result of the recent earthquakes. The aim of his research is to gather data from the recent rockfalls to map out the potential danger zones and quantify rockfall risk around the city. His research will help planners decide which areas will require mitigation of rockfall risk before rebuilding can occur. We visited a few key localities which had suffered damage from rockfall during the February 22nd ‘quake. This property in Heathcote  suffered severe damage from a large boulder that travelled roughly 500 metres from the slopes above, bouncing tens of metres at a time, and clearing a 2 metre fence before entering the house through the garage roof. (Photo 1). Later in the day we joined Marty and Mike  of  Solutions 2 Access who are removing unstable boulders from Castle Rock, a popular climbers venue in the Port Hills. This outcrop was shaken and destabilised by the recent earthquakes, sending many boulders flying down slope towards the Lyttelton Road Tunnel entrance. Many other boulders were left precariously perched on the rock face, posing a risk to motorists on the road below, hikers and climbers. Marty and Mike have been contracted by Opus Consultants to remove these rocks which they do by levering them off with a crowbar or by other mechanical methods.(This is known as ‘rock popping’). In the second photo, Marty has just sent large boulder off the edge of the cliff. Chris is interested in analysing the rock fall trajectories as part of the hazard mapping.work. My job was to record video footage of the falling boulders as they were released from the cliff and hurtled down the slopes. This will improve our understanding of how the boulders travel, including  their bounce heights, velocities and angular rotation, which is important when analysing their destructive potential. Here you can see the dent in the hillside caused by a flying boulder impacting on the surface. At the end of the day we went further along Summit Road to the area below the Gondola cable car. The road was covered with rockfall debris that had been shaken off the cliffs just above. The rocks had broken through the metal safety barrier, and some of them had travelled all the way down as far as the lower cable car station about 1 kilometre away. It was interesting to observe the impact craters in the road. The last photo shows a rock deeply embedded in the asphalt – a sobering impression of the power of a falling rock. Check out the video of Chris’s rockfall research in Christchurch:

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Rockfalls and slips in Christchurch

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This week I have been with Garth Archibald, surveying areas in Christchurch that have been affected by rockfalls and slips. These surveys provide data which is used to calculate the stability of cliffs and slopes, and this provides useful information to planners and geotechnical engineers. At Redcliffs, Garth set up his laser scanner to make a 3D scan of the rock face. Houses in this area suffered catastrophic damage from rockfall during the February 22nd quake. Click here to listen to Radio NZ’s Morning Report interview with Garth at work at Redcliffs. The laser scanner sends out about 11000 laser pulses per second. The time it takes for the light to be reflected back to the scanner, gives a very precise measurement of the distance to each point, allowing Garth to make high resolution scan images. He will compare the results with those of a previous survey to see if any areas of the cliff are bulging or tipping over, if cracks are opening up, or if there have been any further rock falls. Another area we worked in was part of Hillsborough where a large area of hillside slipped during the earthquake. This time we used a GPS (Global Positioning System) unit to precisely locate several points. These are being re-surveyed regularly to better understand the nature of the slip. In this photo Garth is setting up the GPS base station at a survey point well clear of the slipped area. In the final photo, Garth is taking a GPS reading at the lower end of the slip. Here the ground has been compressed, and you can see how it has ridged up along the driveway. The fence has also buckled by the compression. .

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New Zealand’s Alpine Fault

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 For the latest on the Alpine fault drilling visit Rupert’s Blog This NASA photo of the South Island of New Zealand shows the green of lowland vegetation contrasting clearly with snow in the mountains of the Southern Alps. The straight edge of the mountains is the line of the famous Alpine Fault. This fault is the boundary between the Pacific and Australian tectonic plates which are sliding past each other in this region at an average rate of about 40 mm per year. The Alpine Fault is a globally significant feature and similar in character to the San Andreas Fault in America or the North Anatolian Fault in Turkey. Every 200 – 400 years the plate movement is accomodated by a violent earthquake of about magnitude 8, and dislocation along a segment of the fault of roughly 8 metres. The last big earthquake rupture occurred in 1717 AD. Most of the fault movement is sideways, but a portion of it is vertical, and has uplifted the mountains on the eastern side to reveal exposures of the rocks along the fault that have been buried and altered over millions of years. The second image shows a slice of this metamorphic rock with white streaks of quartz, black mica and a red garnet crystal that is about 5mm across.   Rupert Sutherland at GNS Science is one of the leaders of the Deep Fault Drilling Project (DFDP) which is about to drill into the Alpine Fault. Many other research organisations are involved in this very large, multi year project. To listen to a short radio interview of Rupert talking about the project go here. From next week, the  DFDP project will start by drilling two shallow (150m) boreholes through the fault near Whataroa on the West Coast. Rocks will be sampled and analysed and instruments will be left in the ground as part of a long term monitoring programme.  In future years this reasearch will be extended by drilling down several kilometres. In the photo of Rupert he is holding a specimen of fault breccia – a bit of rock that has been fragmented by rupturing of the Alpine Fault. In the close up image you can see how the rock is broken up. The dark patches are where some of the rock was melted and then solidified again in the spaces between the fragments.

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Tsunami Video

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New Zealanders know by first hand experience that living on top of a plate boundary makes life unpredictable. The recent earthquake in Christchurch was just the latest example of that. I recently had the privilege of interviewing several Kiwis who had experienced first hand the power of a tsunami. Luckily for them they all escaped with no more than cuts and bruises, but many around them were not so fortunate. These tsunami events were overseas – in Thailand 2004 and Samoa 2009. However, it is worth remembering that New Zealand is one of the most ‘at risk’ countries in the world when it comes to tsunami hazard. In case you haven’t seen it on our GNS Science Youtube Channel here is a video of the vivid tsunami accounts, hosted by Hamish Campbell:

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The Wellington Fault with LEARNZ

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LEARNZ is a unique kiwi organisation that runs ‘virtual’ field trips for primary and secondary schools in New Zealand. Using videos, audioconferences and internet based information, school kids are able to interact with scientists and other expert professionals in different parts of New Zealand. LEARNZ even runs virtual field trips to Scott Base in Antarctica. Last week, Shelley Hersey and Andrew Penny from LEARNZ were investigating the Wellington Fault. Russ van Dissen, Julia Becker and Hamish Campbell from GNS Science joined me to assist them. We looked at the way scientists work with planners and emergency services to understand the earthquake risk and prepare for the possibility of a ‘Big One’ striking Wellington. There is nothing like a detailed description of the potential impact of a natural disaster to remind you to re- check your personal Civil Defence emergency preparedness! In addition to the many other active fault lines in the region that could cause an earthquake, there is a small but real possibility of a Wellington Fault earthquake occurring. This would cause a rupture along the fault line with perhaps 5 metres of sideways movement and one or two metres of vertical dislocation. Houses built across the fault would be ripped apart, and the whole city shaken violently, resulting in severe building damage, streets full of glass and other debris, broken water, gas and electricity supplies, roads, railways and the ferry terminal out of action and communications largely cut off. Did you click on that emergency preparedness link yet? Over three days we visited a number of city viewpoints and structures, the emergency operations centre of the Wellington Regional Council, the fault line itself, and the water supply lakes at Te Marua. It was reassuring to see how much thought and effort has been put into planning for the earthquake risk by the authorities. In this photo of the place where the fault runs right below the Thorndon overbridge and the Wellington Railway, you can see the steel re-inforcement casings around the motorway support pillars and the large concrete slabs that are designed to prevent the motorway segments from collapsing. The take home message is very much that local government and other organisations are doing their bit, and it is up to us individuals to make sure that we have our personal survival plans in place as well. Over one hundred school classes participated in the event. The GNS Science website has a lot of information about the Wellington Fault, including a tour guide, a fault line field trip, a photo gallery , a Google Earth flyby video as well as our Wellington Fault short doco movie:

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White Island 2

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See the video of our visit to White Island: Here’s a bit more about what we did during our day on there: Karen and Agnes set off with their water monitoring equipment, whilst Brad, Steve and I started the elevation survey, measuring height differences between an extended series of fixed points that had been marked by wooden stakes driven into the ground. Whilst Steve held the survey pole, Brad aimed his leveler at it from an adjacent measurement station and was able to read off the height difference between the two points. By sighting between the points in this way, we continued our survey past some very loud and active fumaroles, in a broad area towards the crater lake. Occasionally we stopped to take photographs of interesting features, or discuss the history of the formations around us. Once or twice we were enveloped in steam and gas from the fumaroles, and rained on by acidic water droplets (acid rain) that gave a burning, prickling sensation to my eyes. Past measurements have shown that the ground near the crater has been rising by two or three centimeters every three months for several years, mainly due to an increase in heat in the ground. From our measurements we found that the hottest area of ground near the most active fumaroles had risen up to a maximum of 50mm since the last survey, with the amount of uplift reducing quickly a short distance away. These results show continuity with the long term trend of uplift. Almost towards the end of the survey, we met up with Karen and Agnes, and I watched them sampling the water from a very active hydrothermal spring that was gushing and splashing nearby. To make a variety of measurements of the water chemistry and isotopes, they scooped water out of the spring and put it into various sampling bottles. Once our survey was done, Brad and I walked over to the lower of two webcams to give the glass a wipe, as the photos had been getting quite fuzzy due to a build up of dust. There in front of the camera was ‘Dino’ in real life. He is a small dinosaur, apparently famous the world over for having arrived mysteriously to take up residence in full view of White Island’s Crater Webcam some years ago: see http://www.geonet.org.nz/volcano/activity/white-island/cameras/whiteisland-latest.html Before we returned to the helicopter, we walked through the ruins of the old sulphur mine, where there were rusted machines and derelict buildings. Finally we were ready to leave and as we turned in a wide loop above White Island, I was very impressed to have been able to have had such a close encounter with such a remarkable place.

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White Island

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Last week I visited the GNS Science office at Wairakei, just outside Taupo. This is where a lot of research is done into New Zealand volcanoes and geothermal fields. First up this morning was a trip to White Island, One of the most frequently active volcanoes in New Zealand, where I assisted a small team of volcanologists on one of their routine visits. The purpose was to test the chemistry of the groundwater appearing out of numerous springs around the crater area, as well as to survey the ground surface elevation to check for sinking or uplift. In the team were GNS scientists Karen Britten, Agnes Mazot, Brad Scott and Steve Sherburn. White Island is 50km north of the Bay of Plenty coast, visible from nearby towns and often seen to be emitting a plume of steam. From the mid seventies to the year 2000 it was frequently in a state of eruption. Since then it has quietened down to become relatively peaceful for the last few years.For our visit we flew by helicopter from Rotorua, first across beautiful farmland and large pine forests, then out to sea where White Island soon loomed up in the distance. I had seen many photos of the island before but was excited to have the opportunity to actually set foot on it in reality. It is a horseshoe shaped island, with a high surrounding ridge around the inner crater area that includes a large yellow greenish crater lake. This lake formed after the most recent eruption phase and is only about 6 years old. On the South East side the ridge is breached in a couple of places, where the land slopes gently to the sea shore at a low angle. On our arrival we flew in from this side, and landed in the hummocky area a couple of hundred metres in from the shore.Our pilot switched off the engine, and immediately the sound of hissing and gushing fumeroles dominated. There was a strong smell of sulphur and clouds of steam wafting up from numerous points further in towards the centre of the main crater. The ground was littered with blocks of scoria and lava bombs from past eruptions. The photo shows a lava bomb that was molten when in landed on top of another rock, before it solidified.

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