Why was Christchurch so devastated by a rather small earthquake?

New Zealand is a very modern and prosperous country in a known earthquake-prone area. The earthquake that hit was a 6.3, not small but certainly not huge either. So why was there so much damage?

I assume that NZ would have strict building codes and seismically stabilized building, such as you would find in California or Japan.

There was another earthquake, at 7.1, less than half a year ago that damaged a lot of buildings in Christchurch even though it was further away than the more recent one. That may have caused damage to buildings that had not yet been repaired or reinforced before the second earthquake.

All earthquakes are not alike, and the seismic measure does not represent all the information.

Where a quake starts, the depth and the wave pattern, duration and type of material the wave travels through all play a role.

Hurricanes and storms measured in wind speed alone pose the same problem for assessing the danger level. A hurricane with 100 MPH winds might be a mere nuisance, but a Nor’ Easter packing 60 MPH winds could be a nightmare. The direction of the wind and the duration of wind over water (and the size of the storm) tell more than wind speed alone.
You need a bunch of information about the two events beyond the just peak magnitude.

Was Christchurch devastated? I’m seeing figures of 75 confirmed dead so far and 300+ missing. I would expect a city that wasn’t built to a better code to have casualties many, many times larger.

It wasn’t that huge a quake, but it was very close to the city centre in terms of both depth underground and distance on the ground.

Fromthe Telegraph:

Read this article:

“Devastated”, in this case, doesn’t just refer to injuries or deaths. It also refers to the amount of structural damage the city sustained.

I’ve also heard that the city is built on sand and gravel that moves quite a bit when an earthquake comes.

Distance, depth and liquifaction.

The September 2010 earthquake was away from the city center and at a greater depth than the earthquake, even though it was a 7.1 quake compared to the 6.3 just experienced. Add into the mix the area is prone to liquifaction (PDF warning but a really good, detailed poster) and the city is prime for devastating destruction.

To borrow a cliche, it wasn’t the size of the ship as much as it was the motion of the ocean.


It was on the same sand as the earlier quake.

See comments above that distinguish what was different about the two quakes, since the city sits on the same soil as it did before.

I watched some of the linked videos too. It appears the city is mostly nearly intact. This looks more like Loma Prieta than San Vicente–let alone Bam.

Not meaning to wave away anyone’s genuine suffering, just taking issue with the idea that the city was “devastated” because of inferior building.

Is Hollywood organizing multiple fundraisers?

My understanding is that this is the ideal set up for a quake-prone area, if I’m remember my geology class correctly. Unconsolidated ground is much better suited to handle regular quakes.
Though I’m certainly willing to accept I might be misremembering :smiley:

Very good article here in which a Canadian civil engineer discusses the quake and the buildings of Christchurch.
Among other things, he said:

Diosa: one problem with unconsolidated ground is liquefaction, which evidently occured in Christchurch (see Duckster’s post #8).

Even Japan has quite a few older buildings - the Kobe quake of 1995 (6.8 MMS) killed over 5000 people.

Add to that the fact that Christchurch is comparatively old as antipodean cities go: the place was founded in the mid-19th century and there are (or were) a lot of heritage buildings in the downtown area that aren’t as quake-resistant as other construction.

And yes, they did take a pretty big hit from the 7.1 quake last September: we didn’t hear as much about it because thankfully no lives were lost, but it trashed a lot of the built environment in the Canterbury Plain.

(I visit Christchurch often and am very sad about this catastrophe, :frowning: although my godson’s family and all their family and friends are okay so I’m really happy. :slight_smile: Simultaneously, which feels a little weird.)

Apparently even the experts were surprised.

" Maurice Lamontagne, a seismologist at the Geological Survey of Canada, said: "What surprised me most was not seeing the damage to masonry buildings like the cathedral’s bell-tower but to see new concrete buildings crumbling down.

“New Zealand has excellent earthquake standards in its building codes, but those standards were much more stringent on the Alpine fault to the west of Christchurch than in the city, where secondary faults are poorly known.”

He added: “Experts have been surprised that the town itself has been hit.”

For comparison, the 1989 Loma Prieta earthquake (San Francisco) (6.9) killed 63 an injured about 3,750 othes. And the Norridge Earthquake (LA) (6.7) killed 33 and injured 8,700


As noted earlier, Christchurch is a (relatively) old city in this young country. It was not built on a seismically active region (unlike Auckland and Wellington).

They had no reason to expect a large quake, and this latest quake is on another, separate and previously unknown faultline.

As has been pointed out by others the Christchurch quake was very shallow (5 km) and very close to the city centre (about 10km).

To complete the comparison:

Northridge was 19km deep and 31km away from the city centre. So while the magnitude was about 4 times greater the earthquake was about 3 times deeper and 3 times as far away.

Loma Prieta was 18 km deep and almost 100km away from downtown San Francisco. So 8 times the magnitude of Christchurch but 3.5 times deeper and almost 10 times as far away.