Hi Martin,

Dave Nelson sent the following, which alludes to the geology:

Hey Jerry,
                  its a pretty complex subject,  and the amount of shaking 
and liquefaction is proportion to a number of  things, including....distance 
from the quake  ....  attenuation of the waves magnitude of the quake  .... 
size affects the period of severe shaking soil type   ....  soft, hard, 
gravels etc etc

I know Christchurch city very well, having worked there, visited there many 
times over the years and my 2 kids (early 20's) still live there and went 
through  this quake.  A large portion of Christchurch is basically built on 
a swamp, it is very
soft wet soils being an estuary area of 2 rivers.  When I worked for telecom 
there and were doing cable laying,  you only had
to dig down a couple of feet and you holes/trenches started to slowly fill 
with water.

So the 3 factors above and others not mentioned all play a part in how much 
damage is going to occur.
Magnitude therefore period of intense shaking is very signif. as they found 
out in that huge quake in Mexico in 1985  the M8.1 was a long way from the 
city,  but the combination of the alluvial basin the city sat on,  the 
period of shaking  are what contributed to the horrific numbers of deaths 
and severe damage (not to mention the crappy building construction)REMEMBER 
.... New Zealand is pretty anal about earthquake preparedness...very strict 
building codes  etc etc

cheers
Dave Nelson
Sydney
Ex New Zealand

Regards,
Jerry

--------------------------------------------------------------------------------



  ----- Original Message ----- 
  From: Tangazazen@.......
  To: psnlist@..............
  Sent: Monday, September 06, 2010 2:19 PM
  Subject: New Zealand earthquake



  Hi All,


  There has been some discussion  on the latest New Zealand earthquake and 
considering the magnitude, luckily no loss of life but considerable damage. 
Most earthquake damage is due to the surface wave. The attenuation of 
Rayleigh waves is significantly less than that of a body wave, approximately 
1/ root of distance.  For gravel and sands though, seismic velocity are low 
but the dispersion can be quite high, that is the energy appears in lower 
and lower frequency with distance. Certain types of clay particularly when 
wet can exhibit thixotropic properties, that is a fall in viscosity with 
shear stress as at Mexico city. Does anybody know of the geology of the 
area?

  Resonance can be damaging to building and as a general rule of thumb is 
about 10 c/s divided by the number of floors.  Given the distance from the 
epicentre one would expect the taller building to have sustain the most 
damage.
  Is there anybody in Christchurch who can though some light on any of this?


  Martin Page 







Hi=20
Martin,
 
Dave Nelson sent =
the following,=20
which alludes to the geology:
 
Hey=20
Jerry,
          &nb=
sp;      =20
its a pretty complex subject,  and the amount of shaking and =
liquefaction=20
is proportion to a number of  things, including....distance from =
the=20
quake  ....  attenuation of the waves magnitude of the =
quake =20
..... size affects the period of severe shaking soil type   =
..... =20
soft, hard, gravels etc etc

I know Christchurch city very well, =
having=20
worked there, visited there many times over the years and my 2 kids =
(early 20's)=20
still live there and went through  this quake.  A large =
portion of=20
Christchurch is basically built on a swamp, it is very 
soft wet =
soils being=20
an estuary area of 2 rivers.  When I worked for telecom there and =
were=20
doing cable laying,  you only had 
to dig down a couple of feet =
and you=20
holes/trenches started to slowly fill with water.

So the 3 =
factors above=20
and others not mentioned all play a part in how much damage is going to=20
occur.
Magnitude therefore period of intense shaking is very signif. =
as they=20
found out in that huge quake in Mexico in 1985  the M8.1 was a =
long=20
way from the city,  but the combination of the alluvial basin the =
city sat=20
on,  the period of shaking  are what contributed to the =
horrific=20
numbers of deaths and severe damage (not to mention the crappy building=20
construction)REMEMBER ... New Zealand is pretty anal about earthquake=20
preparedness...very strict building codes  etc =
etc

cheers
Dave=20
Nelson
Sydney
Ex New Zealand
 
Regards,
Jerry






  
----- Original Message ----- 
  From:=20
  Tangazazen@....... 
  
To: psnlist@.............. =

  
Sent: Monday, September 06, =
2010 2:19=20
  PM
  
Subject: New Zealand =
earthquake
  


  
 
  
Hi All,
  
 
  
 
  
There has been some discussion  on the latest New Zealand =
earthquake=20
  and considering the magnitude, luckily no loss of life but =
considerable=20
  damage. Most earthquake damage is due to the surface wave. The =
attenuation of=20
  Rayleigh waves is significantly less than that of a body wave, =
approximately=20
  1/ root of distance.  For gravel and sands though, seismic =
velocity are=20
  low but the dispersion can be quite high, that is the energy appears =
in lower=20
  and lower frequency with distance. Certain types of clay particularly =
when wet=20
  can exhibit thixotropic properties, that is a fall in viscosity with =
shear=20
  stress as at Mexico city. Does anybody know of the geology of the =
area?
  
 
  
Resonance can be damaging to building and as a general rule of =
thumb is=20
  about 10 c/s divided by the number of floors.  Given the distance =
from=20
  the epicentre one would expect the taller building to have sustain the =
most=20
  damage.
Is there anybody in Christchurch who can though some light =
on any=20
  of this? 

  
 
  
Martin Page