After last years events, the populous and civil defense know exactly what to do – and have done and are doing it. With all sympathy to the devastated individuals, it still could have been even worse had the building standards not been as high as they were.

Buildings built 100+ years ago, 99+ years before Christchurch was considered a quake zone – have not fared well, that’s true.

What gives? The foundations, that’s what.

The issue with the Richter scale is valid – which is why folk who care nominate a replacement measure (Mercalli) that apparently takes into account real intensity, not just magnitude. Last years 7.1 (Richter) was bigger to the Haiti one on paper, but had no casualties. Now a 6.3 (Richter) at a much closer depth, distance and speed has a *much* different effect.

This is different from the Modified Mercalli Intensity scale (MMI) you mention. Both are in current use. Mercalli scale does what you suggest, it rates the intensity for a given location.

But you can’t assign a single MMI number to an earthquake, because the rating depends on the location. You’d give different numbers for different affected regions – it’s higher close to the epicenter, and lower as you get further away (with many variations possible depending on the geology, naturally). Thus you see the “Shake Maps”, with color-coded areas showing where the most shaking occurred, based off of the MMI for each area.

I have an MS in geology, and I went to grad school in Southern California and took courses specifically on seismology and earthquake physics :)

My first day and hour of teaching up the hill at varsity was swinging in an 8 storey building because of the earthquake to the east of us, http://www.geonet.org.nz/earthquake/historic-earthquakes/top-nz/quake-10.html

The images of the CTV building are hard to view. The blanket declaration that no one is alive there was callous in the least. Glad to hear today that others continue to search for survivors (and at least one was found).

We lived in Canoga Park and got out just before the ‘Big One’. All those ground floor apartments with big sliding glass doors were pancaked by upper floors, and that lack of structural integrity, including the ground floor apartment we had been living in. Same goes for apartments with garages fronting on alleys, you’ll lose the car in the garage, and anything in the room above the garage as the apartment pancakes down, why, kinda like a house of cards!

Forewarned is forearmed: but against such a foe, it is often not enough.

I hope the New Zealanders recover quickly: I am sorry for their losses.

Building standards in NZ are very high with regards to earthquake proofing. In last September’s earthquake many modern houses suffered cracks but did not collapse; this contributed to low injury levels.

However, my partner works in the construction industry and over the past 25 years has often had to mediate between architects and engineers over design issues, with the architects pushing the engineers to reduce structural strength features that interfere with aesthetics. He tells me that many commercial buildings in Auckland NZ (where we live) would not survive a major earthquake.

Fortunately Auckland is not on a faultline – but then again, until last September’s earthquake, no one knew Christchurch was on one either.

The Mercalli scale quantifies the violence of shaking at specific locations. Mercalli VIII and IX (or above) are the dangerous levels for well-built, seismically-resistant structures. (Vulnerable structures like unreinforced masonry – brick, stone, adobe – are also susceptible to Mercalli VII.)

As you can see on the PAGER maps and charts, many more people were exposed to dangerous levels of shaking in the current quake, even though it had a smaller magnitude and its shaking affected a smaller area than the September quake.

Location, location, location.

Sympathies to everyone trying to get their lives back together for the second time in less than a year.

How much of Chch is on unconsolidated sediments (like those of Northridge (?), CA) so damage might be worse? Also, any idea why some buildings look fine and others are rubble (photo bias, sediments, building standards)?

Christchurchquakemap, New Zealand)

The worst part is that you couldn’t really tell, in the first couple of seconds, whether this was a typical aftershock, usually a full order of magnitude lower than the mainshock; or if it might be a repeat of the mainshock. The first second or two are pretty much identical either way.

(Aftershocks as large as or larger than the mainshock are unusual in plate-margin quakes – but not impossible).

Much was made in the immediate aftermath of Northridge about how cheerful and helpful and cooperative everyone was, working together to help each other cope with the disaster.

But, I’ll tell you: by about three or four days later, when the initial novelty had worn off, and no one had had a decent nights’ sleep due to the hourly-or-so aftershocks, people were a LOT less cheerful. :-)

It’s really odd to be stumbling around among several million people, every one of them cranky and tired and sleep-deprived.

My advice is to be generous in giving each other the gift of slack; and remember that, like all things, this too shall pass.

Christchurch has seen a lot of liquefaction (we learned that word last September) and I gathered from last time the way the waves bounce around in the sandy ground mean a very uneven shake depending where you are.

The ground and the building will have been unevenly undermined in September (and since) too.

Self-promo: We’re working hard on from-the-horses mouth coverage at scoop.co.nz/

Fortunately Auckland is not on a faultline

It is on a volcanic field though.

Ian Wells

also live just north of baja, CA. Last week we had a 5.5 during a meeting. Dude didn’t skip a beat.

Now, I realize the scale is logarithmic. But the range from ‘can’t be bothered to miss a slide’ to ‘ZOMG panic’ is STILL more than 10.

So I don’t think maggie’s original question–why is this a problem?–has been answered.

Christchurch doesn’t have tall buildings, though I suppose it has older buildings it holds on to to seem more English. I’m sorry, but when a small earthquake kills people–that’s a human disaster, not a natural one.

But NZ…I genuinely do think they expect quakes and are prepared. So what gives?

The issue with the Richter scale is valid – which is why folk who care nominate a replacement measure (Mercalli) that apparently takes into account real intensity, not just magnitude.

But even the Mercalli won’t answer the most critical questions – namely, “How much damage, how many casualties?” – because intense shaking that occurs in empty quarters or lightly populated areas with only a few lightly-built, quake-resistant structures will still cause less far damage and fewer casualties than identical (or even less-intense) shaking that strikes densely-populated areas packed with vulnerable buildings.

Both the September Mag. 7.0 and the current Mag. 6.3 produced maximum Mercalli Intensities of IX – and the 7.0 produced those intensities over a much larger area.

But the Mercalli VIII-IX areas -the ones where the bulk of the damage will occur – from the 6.3 affected far more people and many more vulnerable buildings, because it struck directly under the city center, where, not only is the population density much greater, but there are many more vulnerable buildings, especially late 19th/early 20th C. multistory unreinforced masonry
buildings.

Look at the PAGER population exposure charts linked above. The estimated Mercalli VIII-IX exposure in the 7.0 was only about 22k people, while the estimated VIII-IX exposure in the 6.3 was about 317k people.

Combine that with more vulnerable buildings in the city center, and it’s easy to see why the smaller quake did more damage and resulted in more casualties.

(And that, by the way, is the whole purpose of the PAGER estimates – to try to get an early, reliable estimate of just how serious a quake is in terms of damage and casualties, rather than relying on numbers that can only tell you how much total energy was released or how intense the shaking was.)