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Magnitude 6.3 Earthquake Strikes New Zealand

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A 6.3 magnitude earthquake struck the south island of New Zealand near Christchurch on February 21, resulting in 75 lives being lost. This earthquake was an aftershock from the Sept. 4th magnitude 7.0 earthquake that occurred in nearby Darfield last year. So why did this lesser magnitude earthquake result in more damage and lives lost? 

Jennifer LaVista spoke with U.S. Geological Survey seismologist Robert Williams, who spent time in New Zealand after the Sept. quake.




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[Intro Music]

Jennifer LaVista: A 6.3 magnitude earthquake struck the south island of New Zealand near Christchurch on February 21st, resulting in 75 lives being lost. This earthquake was an aftershock from the September 4th 7.0 magnitude earthquake that occurred in nearby Darfield last year. That earthquake resulted in 1 person dying from a suspected heart attack.

So why did this lesser magnitude earthquake result in more damage and lives lost? I’m Jennifer LaVista, joining me is U.S Geological Survey seismologist Robert Williams who spent time in New Zealand after the first September quake.

Rob, can you please tell us why this recent earthquake was more destructive?

Robert Williams: It’s about distance and depth of earthquake locations. The magnitude 6.3 earthquake was much closer and much shallower than the magnitude 7 that happened last September. So Christchurch experienced much stronger shaking from the magnitude 6.3 and thus more damage.


Jennifer LaVista: Can we expect to see more aftershocks?

Robert Williams: You can. The aftershocks sequence from the magnitude 7 could last for a year or more. It wasn’t surprising to get a magnitude 6.3 aftershock. And now that quake in itself has generated a new sequence of aftershocks that will go on for months.

Jennifer LaVista: So is it possible that we could see more aftershocks for another year from now?

Robert Williams: It certainly is. Typically, there is a decline in the number and frequency after the main shock hits but they could last for months and months.

Jennifer LaVista: And will they probably be lesser magnitudes?

Robert Williams: Yes, typically they are. The main shock 7.0, and then the biggest aftershock you would expect would be about 1 point smaller and so the 6.3 fits roughly in that scenario.

Jennifer LaVista: Now you went to New Zealand after the September quake.


Can you shed some light on what some of the buildings look like around that area?

Robert Williams: Christchurch is the second largest city in New Zealand and it looks like a small U.S. city. It’s got a variety of buildings from modern skyscrapers to 75 to 100 euro brick buildings so there’s a full range of building types. It reminded me a lot of U.S. cities especially areas of brick buildings and those, in fact, suffered the most damage in that magnitude 7 and then the magnitude 6. 3.

Jennifer LaVista: Can we learn anything from these observations of the buildings as far as maybe building codes?

Robert Williams: We can and a lot of people are studying that now – engineers, they have been looking at the performance of buildings using the seismic network that the New Zealand geologists and seismologists had deployed prior to the earthquake to measure ground motions and engineers can then use that information knowing what the buildings experienced.


So it’s really helpful to have that network to help them figure out future performance of buildings.

Jennifer LaVista: What would happen if there was a similar earthquake here in the U.S.?

Robert Williams: If it happened in California, I think you could expect similar consequences. If it happened in the Eastern U.S., close to a big city, then it could be worse, I think.

Jennifer LaVista: And you’re talking about the New Madrid fault line in that area?

Robert Williams: For example – that’s right. The magnitude 6.3 really damaged a lot of brick buildings in Christchurch and those types of buildings are the ones that you see up and down Main Street in the Central United States so it’s a type of building we’re very concerned about. It was constructed without any consideration of seismic hazard 75 or 100 years ago.


Jennifer LaVista: Now where can folks go if they’re interested in learning more about earthquake preparedness or maybe building codes in their area?

Robert Williams: The Red Cross is a good source for earthquake preparedness from what to do as a family unit to community level and there are guidelines on the Web and literature there. The USGS has information about earthquake hazard and then reproduces some of the information from the Red Cross about preparedness.

Jennifer LaVista: OK.

Robert Williams: FEMA is another place to go to get information about building preparedness for businesses and mitigation.

Jennifer LaVista: Now I understand there’s some events that will be taking place over the next few months that communities and families can participate in. Can you tell me some more about that?

Robert Williams: That’s right. Coming up on April 28th is the Great Central U.S. ShakeOut. It’s being sponsored CUSEC out of Memphis as well as the USGS. And in that event, they’re encouraging people to sign up beforehand, go to their website –


Sign up, learn about preparedness and mitigation as well as participating in the event on April 28, which will emphasize a drop cover and hold and when an earthquake happens. 

And I know that people in New Zealand during the magnitude 6.3 event a couple of days ago reported that they ducked under their desk and it helped them survive… earthquakes as the buildings collapsed.

Jennifer LaVista: Wow.

Rob, is there anything else you’d like to add?

Robert Williams: Yeah, I would. The magnitude 6.3 near Christchurch a couple of days ago, you saw a lot of damage to buildings especially older brick buildings. We’ve seen this over and over throughout my lifetime. Damage to buildings like this, engineers will tell you they know how to make buildings that won’t fall down on people right now.

They know how to do seismic upgrades and retrofits to older buildings which would go in and strengthen the brick frames and help them to survive earthquakes.


It’s a matter of cost and commitment by the communities to decide to do this. So it is an option. It’s a tragedy these things happen. Every time they do happen, we do learn a lot and going forward, I know that this earthquake will also be a learning experience for us.


Jennifer LaVista:  Rob, thanks so much for being here.

Robert Williams: OK, you’re welcome

Jennifer LaVista: I’m Jennifer LaVista and this is USGS CoreCast. CoreCast is a product of the U.S. Geological Survey, Department of the Interior.

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