Some images I took this morning, on an early walk through Christchurch City Centre. I offer my best wishes to the folk of Christchurch and other Canterbury towns who are still patiently rebuilding their livelihoods, three years on from the 22nd February 2011 aftershock. We Remember:
Christchurch City Centre, Three Years On Read More »
We have a new GNS Science video today that explains how scientists locate the source of an earthquake and then calculate the magnitude. John Ristau, from GNS Science’s GeoNet programme talks through the steps of the process… And in case you missed this earlier video, here is Matt Gerstenberger, describing how earthquake forecasts are made using statistics derived from global aftershock sequences:
Where was that earthquake and how big was it? Read More »
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.
Christchurch Quake Q&As Read More »
There has been a lot of ongoing scientific work recenlty to assess Christchurch’s future geological risks. In our latest video Vaughan Stagpoole explains the esoteric arts of Geophysics and what the surveys can help us to find out.
Christchurch Geophysical Surveys Read More »
In this video Garth Archibald explains the use of a laser to monitor rockfall hazards in built up areas around Christchurch City: In the second video, Chris Massey analyses rock fall trajectories in the Port Hills to calculate future risks to housing:
Videos of Christchurch Rockfall Research Read More »
There are a number of urgent scientific studies being carried out around Christchurch to help inform decision makers involved in the repair and recovery process following the recent earthquakes. These projects are being co-ordinated under the Natural Hazards Research Platform which is a collaboration of many of New Zealand’s research institutions (universities and Crown Research Institutes). One of these thirty ‘recovery projects’ is aiming to gain a more detailed understanding of the subsurface geological structure of the area using geophysical methods such as seismic reflection, magnetism and gravity measurements. Although we usually think of the gravitational force of attraction at the Earth’s surface as being something uniform wherever our location, there are actually subtle variations in different places. These depend on our distance from the equator (latitude), our altitude above or below sea level, the nearby landscape topography, and also the density of underlying rock masses in the crust below us. Last week I joined a small GNS Science team who have been making a gravity survey over a wide area around Christchurch City and Canterbury. In the second photo, Vaughan Stagpoole, Jiashun Yu and Dan Barker are setting up the GPS base station at a survey mark, to calibrate the GPS location measurements of the gravity survey. Measurements are made using a gravity meter that contains a very precise spring scale and weight. Minute changes in the force of gravity on the weight result in changes in the extension of the spring and gives a measure of the gravity at a particular location. This is read off on an electronic gauge and verified on a tiny scale in the meter that is observed using a magnifying lens. When readings are taken over a wide area, and latitude, and altitude, as well as local topography are factored in, areas of anomalous gravity can be mapped and interpreted in terms of geological structure. For example, faults completely hidden beneath the sedimentary strata of the Canterbury plains, that have offset underlying high density rocks, will have a distinctive gravity characteristic that is different to areas where the underlying rocks are uniformly flat. The mapped gravity is used in conjunction with other geophysical observations to get a 3D picture of the subsurface. Data from different geophysical surveys or other sources (such as aftershock locations) are then overlaid on top of the gravity map to help distinguish significant features. We can look at some earlier surveys to illustrate this:. This is the present geological map of the Christchurch area, with different colours denoting the different rock types that occur immediately below the surface soil. The pink colours show volcanic rocks such as old lava flows that make up the Banks Peninsula, whilst the yellow and buff colours are sediments such as gravels that have been eroded off the mountains and laid down by rivers across the Canterbury Plains. Red lines are surface rupture faults, including the Greendale Fault in centre left, that ruptured during the September 4th earthquake. (The fault under the Port Hills that moved on February 22nd is not shown here as it is a ‘blind’ fault that did not extend to the surface). This diagram is a gravity map of the same area. It was compiled recently from data collected some years ago. The colours show gradients of gravity intensity. You can see that quite a number of features become visible that are not seen on the geological map. Several of the linear structures are caused by fault lines criss-crossing through the basement rocks underneath the superficial rock deposits. If you click on the image to enlarge it, you will see many little red dots. These are the measurement stations where the actual gravity readings were taken. You will notice that there are significant gaps in some places where data from adjacent stations is extrapolated to fill in the map, rather than actual readings.These are the places where the present gravity survey is being carried out in order to add to this pre-existing data and fill out the missing details. The last image shows the distribution of aftershocks superimposed on the previous gravity map. (The aftershock data is derived from the GeoNet website Quake Search facility). This helps us to find relationships between basement rock types, their distribution and structure, and the fault ruptures that have been causing the recent earthquakes. These diagrams were compiled by Bryan Davy who is a geophysicist at GNS Science, specialising in the use of gravity and magnetic data and the use of interactive mapping software. When the present gravity survey is completed, along with the seismic and magnetic surveys, the added information will further our knowledge of the distribution, length and alignment of fault lines in Canterbury. This information will be included in models that will help evaluate the potential size and frequency of future earthquakes.
Canterbury Gravity Survey Read More »
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:
Rockfall impacts from the Christchurch ‘Quake Read More »
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. .
Rockfalls and slips in Christchurch Read More »
If you are in Christchurch and need basic information and updates about the emergency response go to the Environment Canterbury Earthquake Website. Whilst many scientists are busy at GNS Science with seismic data and interpretation of the physical and social impacts of the earthquake in Christchurch, everyone here is feeling sympathy for those still struggling to cope with the aftermath and continued aftershocks. The image shows the ground shaking intensity across New Zealandas measured by the GeoNet network of seismometers during the magnistude 6.3 quake yesterday. (Click on the image to enlarge.) For an updated time lapse map of the aftershocks have a look here.
Christchurch Earthquake Feb 22 Read More »
Julia Becker is one of the Social Scientists at GNS Science. Her role is to understand the human response to natural hazards, and she works with other scientists and organisations to help plan for future disasters. I asked her to write a diary of her experiences of working in Christchurch in the week following the Darfield ‘Quake: 06/09/2010We arrive in Christchurch, two days after the earthquake. Driving into the city from the airport, much of the city looks quite normal. There are a few chimneys down and damaged brick fences. As we approach the city you start to see more damage, mostly to older brick buildings. Some are just a bit damaged with a few bricks fallen off while others’ facades have completely collapsed. There is quite a wide area around the city that is cordoned off and the cordons are blocked by police officers and military personnel. We have to take a big detour all the way around the city to reach our hotel. Many shops and supermarkets we pass seem to be operating. We drive past a clock tower and it has a big crack in it. At our hotel we drop our gear and then head to visit the city and regional emergency operation centres. They are very busy with many people coming and going, working away hard to respond to the earthquake. After having a few meetings with people to let them know we are here and providing offers of science and research support, we head back to our hotel for dinner and bed. 07/09/2010Small aftershocks in the night occasionally wake me from sleep. I wake at about 6.00 am. While the water is working there is uncertainty over potential contamination so I have to remember to brush my teeth with boiled water. All drinking water needs to be boiled as well. In the morning we reconnect with the regional emergency operations centre and begin to set up an office there from which the scientific research response can be coordinated. I speak briefly to Red Cross volunteers at the regional emergency centre and they say the welfare centres are being well used, with more people turning up after the aftershocks in the night. A little later two of us from GNS obtain official passes to enter the cordoned-off city centre and inspect the buildings from the outside. Many new buildings look like they have stood up well to the earthquake. The Christchurch Cathedral seems pretty sturdy too. There are a number of buildings scattered throughout the centre that have red placards indicating that they cannot be entered due to structural damage. In the afternoon we head out to the suburbs and see the impacts of liquefaction. A few suburbs have experienced significant liquefaction, and sand volcanoes have popped up out of cracks in ground. Residents have already begun to clear away the sand by shovelling it up and placing on the grass verge in front of their houses, and the council is driving by and collecting it in trucks. Port-a-loo toilets have been set up for residents who don’t have working sewerage systems.08/09/2010Sleep is again disrupted by aftershocks throughout the night. This morning before breakfast we are also rattled by a large 5.1 aftershock (scary!), followed by several smaller ones. After breakfast we visit the town centre to observe more of the building damage. We see a whole row of shops made of bricks where the front of the building has simply fallen away on to the pavement in front. Luckily the earthquake happened at approximately 4.30 am so there were few people on the streets at that time and people were not hit by the falling masonry. A restaurant is housed in one of these buildings, and as you look through the gaping hole left by the fallen bricks you can still see the tables set up and ready for customers. In the afternoon we visit the newly ruptured fault near Darfield. You can see where the fault has torn through several roads and fields. The rupture has offset the roads sideways and vertically. Initial repairs to the roads have been made to make them drivable again. You can also see where the fault has offset power pylons, trees and fences. At the very western end of the fault, an electricity substation is perched directly over the rupture and the surrounding fences and gates are twisted, but because the fault is quite distributed at this location the substation appears to still be intact and in working order. At the eastern end of the fault a house-owner is not quite so lucky, with the fault causing building damage to a resident’s home. 09/09/2010 Today we visit a couple of land use planners in Christchurch and discuss issues related to recovery. We discuss having a strategic vision for Christchurch when going into the rebuilding and recovery phase. Following our meeting we take a drive out to Pegasus township, a new subdivision located approximately 30 minutes drive north of Christchurch. Previous studies have shown the site has liquefaction potential. There are a number of houses built there already, and also some empty lots. Pegasus seems to have survived remarkably well and our untrained eyes could not see any significant cracking or liquefaction. It is suggested by the planners we speak to that geotechnical engineering works were undertaken when the subdivision was set up to try and avoid such problems. In the evening I attend a com munity meeting in Darfield. The meeting was set up with the aim of to giving residents information about the earthquake, providing discussion on how they might feel after the earthquake, and providing advice on practical issues that might need addressing (e.g. water pumps, insurance, finance, government support). At the end of the meeting two guest speakers tell a couple of funny tales to provide some light humour to the meeting. The meeting is well attended with nearly 400 people coming along. On our way ho me, driving down Riccarton Road we
Julia Becker’s Observations following the Darfield Earthquake Read More »