Why New Zealand's Earthquake Was So Deadly

By Andrew Moseman | February 22, 2011 10:24 am

At least 65 people died in an earthquake that struck New Zealand’s second-largest city, Christchurch, yesterday. As the city digs out from the rubble created by the magnitude 6.3 quake, some there are worried the death toll could climb into the hundreds. And as seismologists unravel the details, it’s becoming clear why this quake was so much deadlier than previous seismic events in New Zealand.

Photographs and video from Christchurch, a metropolitan area of nearly 400,000 residents, showed people running through the streets, landslides pouring rocks and debris into suburban streets and extensive damage to buildings. Witnesses told of watching the spire of the iconic Christchurch Cathedral come crashing down during an aftershock. One witness called it “the most frightening thing of my entire life,” and television footage showed a person clinging to a window in the cathedral’s steeple. [The New York Times]

This is the second major earthquake to hit the Christchurch area in five months. The one last September was larger, but caused much less damage. It’s another reminder that the depth and location of a quake—and not just its magnitude—make a great difference in how deadly it is. In addition, this one’s epicenter was merely a few miles away from the city center.

Last year’s 7.1-magnitude earthquake was more than 10 times as strong as today’s but caused no deaths, probably because it occurred at greater depth and further away from Christchurch: its epicentre was 70 kilometres west of the city. And the focus of September’s quake was some 10 kilometres below ground – today’s was half as deep. “The ground motion [of the previous quake] had significantly attenuated by the time it reached Christchurch,” says Adam Pascale, a seismologist at Environmental Systems & Services in Richmond, Australia. [New Scientist]

New Zealand occupies a precarious location at the intersection of the Pacific and Australian tectonic plates, seen here. The stresses between those two have created broken fragments beneath the islands. The Alpine Fault, which carries much of the stress beneath South Island (where Christchurch sits), has seen its fair share of major quakes before.

It may take seismologists some time to sort out the specifics of the quake, but a few are already speculating that it happened along the same fault line as the one that caused last September’s event.

Related Content:
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80beats: China Earthquake Increased Stress on Other Faults
DISCOVER: The Next Big Quake

Image: Wikimedia Commons

  • Pubali Batash

    I show all those pictures at http://blogs.sacbee.com/photos/2011/02/dozens-trapped-by-new-zealand.html and videos at http://fms.nu/gnfRcJ. it is really very much shocking. God must help all those people.

  • scott

    Obviously there is not a strong enough building code. I was watching a report last night and someone was talking about how strict NZ is..really? Its not a 3rd world country. This same story plays out all over the world…the steps taken to make quake proof buildings/reftrofit old ones, is very lax. Also, the delays in repairs should be seen as a crime. There were many buildings damaged from the Sept quake that crumbled right away. These should have been torn down immediately, or the government should have implemented a massive, well organized retrofitting. After the 89 quake in SF, there was a large, very damaged brick mid rise building that was fenced off and remained standing for years…busy streets packed with people were all around it..after all the who knows what kind of red tape, it was finally removed.

    It all comes down to cost, here in LA, SF, Tokyo, etc. Yes, you could say 100 people dead out of 400,000 is actually pretty good for the NZ quake, but the death toll could be zero (save someone dying from a heart attack from fear).

    We/I have seen this in 89 in SF, in 94 in LA, sloppy engineering mixed with lowest bidder building, mixed with beating deadlines and you get too many buildings that fail in a quake. The technology IS there to withstand these quakes, shallow or not, its cities, taxpayers, governments, etc that dont want to spend the time and money to build things as they should be, so instead, they get ruined city blocks and dozens of dead people on their hands as well as a bunk economy for a long time. However, there is always enough money around for fancy convention centers, ball parks, new malls, etc.

    There are dozens of highrises in LA that were damaged in the 94 quake that have not been repaired for monetary reasons as well as tenants who dont want to have to move out so work can be done. Many of these buildings were built “quake proof” but with 60’s and 70’s technology..we can remove them now, or remove them, and the bodies inside, after the next 6.5+ quake in the area. Same with historic places like Chinatown in SF…charming, historical societies would balk at removing the charm, but it will be removed, by the earth along with the dead underneath. I have engineer friends and we go Chinatown sometimes when I am in SF…the subject always comes up, its already a disaster, because it will happen.

    A quake like this will happen in many areas, eventually, possibly even the midwest or east coast of he US. People keep ignoring and delaying action that needs to be taken..maybe it is easier to just bulldoze piles of rubble after a disaster than to retrofit and hope it happens when the buildings are empty at an odd hour..

    Pubali – God could have helped them before the quake by preventing it in the first place…face it, God is neutral bud, “he” made a crazy universe that plays out randomly, he does not watch over and control random disasters that occur all around the world. Like watch a mudslide kill hundreds in Bolivia and then swoop in with his might and help save a few left in the mud..or come help with clean up after an F5 sweeps through a Dallas burb.

  • M Burke

    As a survivor of the 89 quake in Santa Cruz, CA, I can only say that the images of NZ look a lot like Santa Cruz in that day. We fortunately didn’t have as many brick constructed buildings.

  • Philip

    Scott, you are talking without full knowledge there. New Zealand does have a pretty strict building code and earthquake proofing is one of the priorities. However Christchurch and Dunedin both have a healthy number of historic buildings that significantly predate the building code and while strengthening generally has been carried out there are limits to what can be done.

    In this latest quake the lateral motion, due to the proximity and shallowness of the quake, hit and possible exceeded a G. That is tough to safely withstand and many newly constructed buildings that were nominally earthquake proof didn’t cope. It didn’t help that many buildings were still in the process of being repaired from the effects of the primary quake and thus in a weakened state.

    It is going to be quite a while before the full analysis of exactly what happened and why the failure rate was as high as it was. Speculation like yours isn’t wildly helpful right now.

  • Shooman

    Okay – a bit of flawed intelligence in that article. The first quake – back in September did A LOT of damage. Yes, it wasn’t so violent because of the reasons stated, but the damage that, that quake did, still wasn’t repaired to this day. Also, and here’s the major reason there were no deaths – the time in which it occured. Around 4am. Very little people are out and about during this time. This was sheer luck. Had it been during the day – we would have been seeing what we are right now. A combination of severe aftershocks also caused the integrity of many standing buildings to become weakened. This quake was just the (extremely heavy) straw that broke the camels back.

  • Jon

    Scott, to my knowledge as a civil engineer, the building codes are designs based on previous large earthquakes all over the world. It is kind of hard to say that the building codes are strong enough or adequate. It is never 100% earthquake proof. It is all based on probability and chance of a certain type of earthquake occurring. Even though this was a 6.3, it was really shallow, which is pretty rare. Also, the building codes are there so that there is adequate time for people to evacuate a building and not for structural survivability.

    Buildings are also difficult to retrofit, especially historical buildings. This would require excavating and creating base isolation systems without damaging the historical structures, or a contractor can provide external retrofitting, which makes the building look ugly. Fortunately in LA, there’s money to create these damage reduction systems for historic buildings.


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