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 »
The recent magnitude 6.5 Cook Strait and 6.6 Lake Grassmere earthquakes were comparable in size to the ‘quakes that rattled Canterbury in 2010 and 2011. This map of peak ground accelerations for the Lake Grassmere Earthquake shows recordings of up to about 0.75g.(or 0.75 the acceleration due to gravity). One of the notorious and extremely damaging effects of groundshaking in Christchurch was the widespread liquefaction and flooding that affected large areas in the eastern suburbs. This occurred in areas where the land was made up of soft low lying sediments by the river or near the coast such as Bexley and Avonside. (photo by Dick Beetham, GNS Science)The most significant damage in Wellington was long the edge of the port where a large section of the road collapsed into the sea. This photo by Graham Hancox of GNS Science, shows the scene after the combined effects of the two recent earthquakes. So what were the effects on the ground near the earthquake epicentres? Are there any areas of soft, waterlogged sediments beside an estuary or river in Marlborough that might be expected to compare with those severely damaged parts of Christchurch? A team from GNS Science went to look at the ground damage alongside the Opawa River, near its confluence with the Wairau River. Dougal Townsend took these photos during their visit: Near to the river, there were several long cracks created by lateral spreading. Sand boils and sand volcanoes had left their mark over the paddocks beside the river. With the help of a spade, one of the sand volcanoes was sliced vertically to show a clean cross section through it. You can see the thin crack in the soil that was opened up during the earthquake, that allowed the sand loaded water to ‘erupt’ at the surface. Compared to Christchurch, these liquefaction effects from the recent Cook Strait and Lake Grassmere Earthquakes are relatively minor. This is an important finding as it shows that the extreme level of liquefaction in Christchurch was not necessarily a typical example of what to expect from future earthquakes in the rest of the country. Scientists now have some more useful data to help to differentiate between the impacts of ‘quakes in apparently similar environments.
Liquefaction Effects from the Cook Strait / Lake Grassmere Quakes Read More »
Dougal Townsend of GNS Science was part of a team that flew over Marlborough to assess the impact of the recent earthquakes on the landscape and infrastructure. Although relatively minor compared to those that impacted the Christchurch area in 2010 and 2011, there were nonetheless some isolated, but significant effects. All these photos were taken by Dougal: Here you can see damage (cracking) to State Highway 1 between Seddon and Ward (near Caseys Road turnoff) following the Lake Grassmere Earthquake. Large landslide in the Flaxbourne River catchment (about 8.5 km west of Ward). Another Large landslide. This is in Miocene mudstone, just south of Cape Campbell. A whole section of the hillside has slipped Bell’s dam near Seddon. Damage (cracking) was sustained during the Cook Strait Earthquake and was exacerbated during subsequent aftershocks and also during the Lake Grassmere Earthquake. The channel was dug to partially drain the dam, to lessen potential flood risk to the town of Seddon, which is 10 km downstream to the NE. A closer view of the cracks along the top of Bell’s dam. alongside the vehicle track This image shows rock fall on a farm track about 2 km southeast of Ward (track goes up to Weld Cone). The rock is Late Cretaceous sandstone and siltstone. Ground damage in Needles Creek, west of Ward. Cracking of the farm track (centre left) is from the Lake Grassmere Earthquake, whereas the minor landsliding of the terrace gravels on the right may be from a combination of storm (rainfall) and earthquake (ground shaking) damage.
Earthquake impacts in Marlborough seen from the air Read More »
Following the earthquakes in southern cook straight, the GeoNet rapid response team left immediately to place seismometers around the area, to allow more detailed monitoring and get better information with which to model the fault ruptures. This meant that when the Mag 6.6 occurred, the enhanced array of seismometers was already in place. Here is a screen shot of the Mag 6.6 Grassmere Earthquake and immediate aftershocks over the following hours: This GeoNet video gives an idea of the number and locations of aftershocks from the 16th to19th August
Lake Grassmere Quakes Read More »
This is a screen shot of the Wellington seismometer from very early on Monday morning 22 July Following the earthquakes in Cook Strait over the weekend, it was impressive to arrive at work on Monday morning, and watch how the GeoNet team, many of whom had been busy right through the weekend, were in full action mode again. Ken Gledhill, the head of GeoNet, co-ordinated two meetings of the scientists and technicians during the day. There are lots of different things involved with understanding earthquakes. These include getting accurate locations and magnitudes, modelling the position and orientation of the fault and the type of fault rupture from the seismic wave patterns of the aftershocks, working out the adjusted stress on nearby active faults and then trying to calculate probabilities of future quakes to inform an ‘awakened’ public… Here is the aftershock map from Sunday evening that shows the relative magnitudes of the quakes and their initial locations in 2 dimensions. Up to today there have been nearly one thousand aftershocks already. As more and more occur and get analysed, a more precise 3D image of the fault(s) involved will be built up. To help get more precise seismic data, the GeoNet fast response team are already in Marlborough, setting up some extra temporary seismometers at carefully chosen locations to ‘fill in the gaps’ between existing permanent stations. Here is a photo of one of the team yesterday, packing one of the seismometers for the trip. To see more photos of what these guys do, have a look here. This is a computer simulation of the seismic waves from the M6.5 ‘quake propagating across the North Island and the adjacent sea floor: New Zealand’s background risk of earthquake probabilities has been calculated for the whole country. Once a reasonably large earthquake has occurred, these background risks of a larger quake increase for a while in the local area, and a sequence of aftershocks follows that typically fits into a fairly predictable pattern of decreasing intensity over time. In the video below Matt Gerstenberger explains how these calculations are made to produce probability tables and maps for future aftershocks. For the latest information about the number and magnitude of aftershocks that have occurred in Cook Strait, as well as forecast probabilities for future quakes, have a look at this GeoNet page
Earthquakes in Southern Cook Strait Read More »
Photo: J.Thomson The windswept coastline between Wellington Harbour and Palliser Bay forms the southern tip of the Rimutaka Ranges. These hills themselves are an extension of the axial ranges that stretch the length of the North Island. This is the view east from Baring Head towards Turakirae Head. In good weather, this rugged environment isthe best place in the Wellington area for bouldering (low level rock climbing), but it is also a spectacular place to witness the effects of tectonic uplift on a coastline. From the end of the Wainuiomata Coast Road, follow the track to Turakirae Head seal colony, which is about 40 minute’s walk. On the way you may notice that there are gentle steps in the landscape running parallel to the shoreline. Photo L.Homer / GNS Science The lines that you can see in this aerial photo are ridges of washed up rocks that have been gradually piled up during many southerly storms. The reason that there are several storm ridges is that the coast has been uplifted by successive earthquakes, thus pushing the shoreline further out and causing the creation of a new ridge after each event. Photo L.Homer / GNS Science At least 5 ridges have been identified. Carbon dating of shells and plant material in the ridges shows that the oldest one (furthest from the sea) is over 7000 years old, with others (shown in the image) dating back to 5000, 2300, 158 years and present day. These are not thought to represent all the uplift events that have affected the area over that time, but simply the ones that have been well preserved. The most recent uplift was during the 1855 earthquake. This involved a massive rupture along the Wairarapa Fault that passes very close to Turakirae Head. It was New Zealand’s largest historic ‘quake, with an estimated magnitude of 8.2. It caused widespread damage, such as numerous massive slips in the Rimutakas, but fortunately few fatalities. A similar magnitude earthquake in Wellington nowadays might be a different matter simply because of the denser population and more developed infrastructure.. For more information on the Wellington earthquake hazard check out the GNS website here Turakirae Head featured on the Coasters programme recently, hosted by Steve Logan who met me there with his film crew from Fisheye Films on his way along to Palliser Bay. The flat path like line extending into the middle distance is the top of the pre 1855 storm ridge. Although very rocky it makes for a reasonable 4WD or walking track. Steve came along on his pushbike and interviewed me about the geological features of Turakirae Head, as well as about its rock climbing attractions.In case you missed the programme on TV1 on Saturday 22nd June, you can watch it online here. As well as Steve and the crew from Fisheye Films, we were accompanied by Sophie and Frank (right in photo) – two local Lower Hutt climbers who were part of the support team. Here is the GeoTrip information for you if you would like to visit Turakirae: www.geotrips.org.nz/trip.html?id=249
GNS Science is very proud to support the NZ ShakeOut earthquake drill on September 26th. Watch the video if you don’t already realise why being aware and prepared for an earthquake is a good idea. The event, which will run right across the country at 9.26am, will prompt all of us to check our plans and preparations against the possibility of a damaging earthquake. New Zealand ShakeOut has been created to help people and organisations get better prepared for major earthquakes, and practice how to be protected when they happen. Everyone will practice “Drop, Cover and Hold”—the right action to take in an earthquake. If you haven’t already registered, help the ShakeOut reach over 1 000 000 participants by clicking here
NZ ShakeOut – why all New Zealanders should participate Read More »
How to Respond to an Earthquake in New Zealand This article has been compiled by Karen Hayes at GNS Science with the help of experts including Julia Becker and David Johnston from the Joint Centre for Disaster Research at Massey University, and Adrian Prowse from the Ministry of Civil Defence and Emergency Management (now the National Emergency Management Authority). All photos are by Julian Thomson. Information about the ‘Triangle of Life’ has been disseminated via a chain e-mail that has been in circulation since the 1990’s. The claims regarding the “Triangle of Life” earthquake response are widely discounted. The “Triangle of Life” is not an advocated approach to responding to earthquakes and has been internationally dispelled as being unsound practice. In modern countries such as New Zealand, most buildings are constructed well and you are more at risk of getting hurt from objects flying around rooms. Therefore people should “drop, cover and hold on” in an earthquake. The New Zealand Ministry of Civil Defence and Emergency Management includes the recommended “drop, cover and hold on” advice on their webpage that you can download: I recommend you print the fact sheet and stick it on your fridge to remind yourself and your family of how best to respond in an earthquake. Let’s just take a quick moment to consider one of the claims in the “Triangle of Life” chain e-mail. It states that children have been killed in past earthquakes because they were under their school desks and these were flattened when the building collapsed. It states that they would have been safe had they been lying beside the desk, instead of under it, where a supposed ‘void space’ should be. Realistically speaking, if the desk was not substantial enough to protect the child under it and was flattened by the collapse of a building, then any void space wouldn’t have been large enough to protect the child lying on the floor next to it either. A child is better off getting under the desk to prevent them from being struck by falling items. In the Christchurch earthquake on 22 February 2011, when children did “drop, cover and hold on” under desks, there were no significant injuries reported from any school in the Christchurch area. Building codes designed to reduce earthquake risk will ensure that buildings are unlikely to collapse in the first place. Why Rescuers and Experts Recommend Drop, Cover, and Hold On (the following is taken directly from the earthquakecountry website) Trying to move during shaking puts you at risk: Earthquakes occur without warning and may be so violent that you cannot run or crawl; you therefore will most likely be knocked to the ground where you happen to be. On that basis, it is best to drop before the earthquake drops you, and find nearby shelter or use your arms and hands to protect your head and neck. “Drop, cover, and hold on” gives you the best overall chance of quickly protecting yourself during an earthquake… even during quakes that cause furniture to move about rooms and even in buildings that might ultimately collapse. The greatest danger is from falling and flying objects: Studies of injuries and deaths caused by earthquakes over the last several decades show that you are much more likely to be injured by falling or flying objects (TVs, lamps, glass, bookcases, falling masonry, etc) than to die in a collapsed building. “Drop, cover, and hold on” (as described above) will protect you from most of these injuries. If there is no furniture nearby, you can still reduce the chance of injury from falling objects by getting down next to an interior wall and covering your head and neck with your arms (exterior walls are more likely to collapse and have windows that may break). If you are in bed, the best thing is to stay there and cover your head with a pillow. Studies of injuries in earthquakes show that people who moved from their beds would not have been injured had they remained in bed. You can also reduce your chance of injury or damage to your belongings by securing them in the first place. Secure top heavy furniture to walls with flexible straps. Use earthquake putty or velcro fasteners for objects on tables, shelves, or other furniture. Install safety latches on cabinets to keep them closed. Building collapse is less of a danger: While images of collapsed structures in earthquakes around the world are frightening and get the most media attention, most buildings do not collapse at all and few collapse completely. In earthquake-prone areas of New Zealand, as in many other countries, strict building codes have worked to greatly reduce the potential of structure collapse. However, there is the possibility of structural failure in certain building types, especially unreinforced masonry (brick buildings) and in certain structures constructed before the latest building codes. Rescue professionals are trained to understand how these structures collapse in order to identify potential locations of survivors within “survivable void spaces”. The main goal of “drop, cover, and hold on” is to protect you from falling and flying debris and other non-structural hazards, and to increase the chance of your ending up in a “survivable void space” if the building actually collapses. The space under a sturdy table or desk is likely to remain even if the building collapses – pictures from around the world show tables and desks standing with rubble all around them and even holding up floors that have collapsed. Experienced rescuers agree that successfully predicting other safe locations in advance is nearly impossible as where these voids will be depends on the direction of the shaking and many other factors. If you receive the email in future…If you receive the “Triangle of Life” email, you should reply to the sender and let them know the advice is wrong, and point them in the direction of correct information about how and why to “drop cover and hold on”! Summary: Do: • Identify safe places at home and
“Drop, cover and hold on” is the best advice… 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 »