New Zealand City Earthquake Risk Estimate

[Patrickrh]

This is an interesting article that I read at another forum. It provides an easy way to estimate the earthquake risk at New Zealand Cities.

Both New Zealand and Aussie building standards predominantly use a Z value to estimate the earthquake risk at locations. The higher the Z value is, the more earthquakes there are in the location and the higher magnitudes they will be.

For example, at Wellington, Z = 0.4, and at Auckland, Z = 0.13, which indicates that the earthquake risk at Wellington is much higher than that of Auckland. This is consistent with our common sense: at Wellington, people are often shaken by earthquakes, while most Aucklanders never experience a noticeable earthquake during their lifetime.

The New Zealand Z values varies from 0.13~0.6, while at Australia which is commonly recognized as a non-seismic country, the Z values of most cities are no higher than 0.12.

It need to be mentioned that at the locations being north to Pukekohe (Z=0.13), the earthquake risk is lower than that of Pukekohe, according to seismic research. But because of the legal requirement, Z =0.13 is assigned to those cities for seismic design, e.g. Auckland, Whangarei.

The Z values of NZ & Aussie locations are as below:

• Kaikoura: 0.42
• Wellington:0.40
• Napier and Palmerstone North 0.38
• Christchurch：0.30 (temporarily After 2011 earthquake)

• Taupo: 0.28
• Nelson: 0.27
• Rotorua：0.24
• Tauranga：0.20
• Cambridge：0.18
• Hamilton： 0.16
• Huntly：0.15

• Pukekohe: 0.13

• Auckland：< 0.13
• Whangare: < 0.13
• Adelaide：0.10
• Geelong: 0.10
• Perth： 0.09
• Melbourne/Sydney： 0.08

[Kbkiwi]

This is an interesting article that I read at another forum. It provides an easy way to estimate the earthquake risk at New Zealand Cities.

Both New Zealand and Aussie building standards predominantly use a Z value to estimate the earthquake risk at locations. The higher the Z value is, the more earthquakes there are in the location and the higher magnitudes they will be.

For example, at Wellington, Z = 0.4, and at Auckland, Z = 0.13, which indicates that the earthquake risk at Wellington is much higher than that of Auckland. This is consistent with our common sense: at Wellington, people are often shaken by earthquakes, while most Aucklanders never experience a noticeable earthquake during their lifetime.

The New Zealand Z values varies from 0.13~0.6, while at Australia which is commonly recognized as a non-seismic country, the Z values of most cities are no higher than 0.12.

It need to be mentioned that at the locations being north to Pukekohe (Z=0.13), the earthquake risk is lower than that of Pukekohe, according to seismic research. But because of the legal requirement, Z =0.13 is assigned to those cities for seismic design, e.g. Auckland, Whangarei.

The Z values of NZ & Aussie locations are as below:

• Kaikoura: 0.42
• Wellington:0.40
• Napier and Palmerstone North 0.38
• Christchurch：0.30 (temporarily After 2011 earthquake)

• Taupo: 0.28
• Nelson: 0.27
• Rotorua：0.24
• Tauranga：0.20
• Cambridge：0.18
• Hamilton： 0.16
• Huntly：0.15

• Pukekohe: 0.13

• Auckland：< 0.13
• Whangare: < 0.13
• Adelaide：0.10
• Geelong: 0.10
• Perth： 0.09
• Melbourne/Sydney： 0.08

Im laughing - no one ever thought Christchurch had a high risk of earthquake (which is exactly what people think about Auckland today, despite its obvious numerous volcanos)

[Patrickrh]

Im laughing - no one ever thought Christchurch had a high risk of earthquake (which is exactly what people think about Auckland today, despite its obvious numerous volcanos)

Those people didn’t think about the earthquake risk in Christchuch must regret when their houses were damaged or their family member are injured or even killed.

This article enable any people to learn something new instead of regretting again.

[eri]

Im laughing - no one ever thought Christchurch had a high risk of earthquake

after many years in ak

the first quakes i felt were in chch

and was only there 18months in the 80s..........nz not called the "shakey isles" in oz for nothing

people who think auckland, 0.13, safe

should keep in mind the newcastle quake in supersafe oz

The 1989 Newcastle earthquake occurred in Newcastle, New South Wales on Thursday, 28 December.^[2] The shock measured 5.6 on the Richter magnitude scale and was one of Australia's most serious natural disasters, killing 13 people and injuring more than 160. The damage bill has been estimated at A$4 billion (including an insured loss of about $1 billion).^[2]

[sidinz]

Im laughing - no one ever thought Christchurch had a high risk of earthquake (which is exactly what people think about Auckland today, despite its obvious numerous volcanos)

That's just plain wrong. I was a member of a Civil Defence rescue team in the late 90s and we used to train for the eventuality of a sizeable earthquake. Even back then, we knew that we were overdue for a big one, and it was a matter of 'when' not 'if.' We also had maps of which parts of the city would liquefy. (I suspect, from memory, that these zones turned out to be an underestimate.)

Admittedly, it was thought that the epicentre would be in the Alps, but it was always known that Chch would get a good shake.

[Courham]

That's just plain wrong. I was a member of a Civil Defence rescue team in the late 90s and we used to train for the eventuality of a sizeable earthquake. Even back then, we knew that we were overdue for a big one, and it was a matter of 'when' not 'if.' We also had maps of which parts of the city would liquefy. (I suspect, from memory, that these zones turned out to be an underestimate.)

Admittedly, it was thought that the epicentre would be in the Alps, but it was always known that Chch would get a good shake.

Yep, CHCh has a long history of sizeable shakes, 1865 (or thereabouts). Also one late 1800s which knocked the top off the cathedral. People's memories are short though and in 20-40 years all will be forgotten by most people and once again they'll build on inappropriate land.

Craig

[Patrickrh]

after many years in ak

the first quakes i felt were in chch

and was only there 18months in the 80s..........nz not called the "shakey isles" in oz for nothing

people who think auckland, 0.13, safe

should keep in mind the newcastle quake in supersafe oz

The 1989 Newcastle earthquake occurred in Newcastle, New South Wales on Thursday, 28 December.^[2] The shock measured 5.6 on the Richter magnitude scale and was one of Australia's most serious natural disasters, killing 13 people and injuring more than 160. The damage bill has been estimated at A$4 billion (including an insured loss of about $1 billion).^[2]

You are right, no cities are absolutely safe because no locations in the world can be fully immune to earthquakes. But with the scientific data based on research, we can know which locations are probabilistically safer.

Certainly, the cities like Whangarei and Auckland could have intensive earthquakes in future. But the possibility is similar to win powerball prize soly, while that possibility of Wellington, is like winning $30 lotto prize. The difference is significant, isn’t it.

Newcastle has the highest earthquake risk among all Austrlian cities (population>5000). Z = 0.11. But the earthquake magnitude is not high, though shallow. The intensive damage is mainly because the buildings are not designed properly for the earthquake. At that time, Aussie did not follow the kiwi earthquake standard, which they do follow now. If that earthquake occurred at NZ, the damage would be much less.

[PTILoveYou]

[McDuck]

It's an interesting pattern.
Almost , I don't know, as if there was something under there.
Some sort of rift, almost as if two giant plates floating on a sea of molten rock were running against each other. Ha.

[donna]

New fault lines along (North Canterbury - up to Seddon) have been found since Monday's quake. Geez as if we need more!

[PTILoveYou]

New fault lines along (North Canterbury - up to Seddon) have been found since Monday's quake. Geez as if we need more!

Based on the GNS graph, I won't be surprised there are more undiscovered fault lines under all those red dots!!!

[eri]

also from GNZ

10 years of deep quakes

[Patrickrh]

Hi Gary, thanks for the graph. It well shows the risk distribution. Nice and easy to tell.

[marklowes]

Looks like east of the ranges get all the really devastating shallow quakes. Makes sense e.g. Napiers devastating quake in 1930s? Wairarapa quake in 1800s that lifed up welly sea bed, chch quake, these recent ones.

Would a 50k+ deep quake be equivalent to being 50k from the epicenter of a very shallow one I wonder?

Wooden houses seem hard to level in any case, just these dodgy buildings with corners cut seem to be the death traps.

[Wayne]

Re Christchurch - earthquakes were expected a lot.
What wasn't expected was a large one so close.
They live beside the Alpine fault - the big one.

As for new faults - all faults were new faults at some time in the past. NZ is really one big fault - that's what produced most of the country.
We always look back at the earthquakes over the last 100 years or so - on a geological time scale that is but a blink of the eye.