Monday night’s 5.5 earthquake rattled many people across the district. For some, the memories of Christchurch came flooding back, but for others it was a portent of what scientists say is set to happen any time from now. In regards to Monday’s rattle, AF8 said, “[Monday’s] earthquake is best thought of as a reminder to be prepared. An earthquake can only be considered a precursor or foreshock to a larger event retrospectively. An event like last night’s shake can’t be used to predict future earthquakes, but they do remind us that we need to be prepared for them.”
The quake was first posted as 6.2 but was reduced to 5.5. Geonet reported, “The Magnitude 6.2 was a preliminary location posted shortly after the shaking, once we had more information we were able to give a more accurate size, depth and location. With larger earthquakes such as this one, you do have to wait a bit longer to get a reliable magnitude as more data is required.” Monday’s quake had 63 aftershocks, with 16 being magnitude three and above, which is considered normal aftershock behaviour following an event of this size.
Of most interest was whether the quake affected the Alpine Fault to which Geonet said, “Probably none, or at least not that we could quantify at present.”
According to scientists who work on the AF8 project (Alpine Fault Magnitude 8) “...scientists have established that the Alpine Fault has ruptured 27 times over the last 8000 years. That’s every 300 years on average. The last significant quake on the Alpine Fault was in 1717. There is no reason why the pattern should change now: in other words the next severe earthquake on the Alpine Fault is likely to occur within the lifetime of most of us, or our children.”
AF8’s Scenario Report is informative but also sobering; “It is expected that a large earthquake in the Southern Alps will lead to a ‘cascade’ of hazards including aftershocks, landslides, landslide tsunami, landslide dams, landslide dambreak outburst floods, debris flows, river aggradation, river avulsion and exacerbated river flooding.”
The report warns of tens of thousands of landslides (i.e. mass movements, including falls, slides, topples, avalanches) will be triggered by the shaking during the main shock and major aftershocks.” Those landslides then dam rivers, causing flooding with debris flows that could last for several years.
Potential tsunami sources could generate waves of several metres high that could produce run-up heights of approximately double the wave height, causing water to inundate lake-shore areas within minutes of the initiating earthquake. AF8 has described Lake Wanaka being like a tea cup that tips from side to side causing tsunamis on both shores — so immediate evacuation is a definite possibility.
To find out more about the Alpine Fault go to AF8.org.nz.
Advice on preparedness is available at www.getready.govt nz and www.otagocdem.govt.nz.
Light up: Your emergency supplies don’t have to be in a kit, but you might have to find them in the dark. Make sure everyone knows where the torches and batteries are.
Stock up: Have a stock of food that doesn’t need to be cooked (canned is good) or something to cook your food on (gas BBQ or camp stove). Don’t forget food for babies and pets.
Fridge first: If the power goes out, eat the food from your fridge first, then your freezer, before you eat the food in the cupboard or your emergency kit.
Water: Keep three days of drinking water stored safely. Additional non-drinking water for cooking and cleaning needs to be stored.
Know your neighbours: Get to know your neighbours. In an emergency they may need your help or you may need their help, and you may be able to band together to get through.
Stay informed: Keep up to date with emergency information by listening to a radio — get one with batteries.
Second meeting place: Agree on a meeting place if you can’t get home. It might be a school, a friend’s place or with whānau.
Pack a grab bag: Have a grab bag at work or in your car. It should have walking shoes, warm clothes, some snack food and a bottle of water. A torch, some batteries and a radio are useful too.