Also, Simply To Be Verbose,
It is my understanding that Eigen mode is simply a fancy
way of saying There is a fundamental sympathetic SYSTEM resonant frequency.
It applies to any mechanical system regardless how complex its physical makeup.
It has always seems so silly to me that people don't just say
resonates instead of always having to give credit to
people who in the past have simply stated the obvious.
If you need to cite a genuine mathematical set of equations
then I understand the reference to Eigen who was most probably
some famous dead person from the distant past.
So like the earth/ground showed a natural resonance at whatever period or frequency.
Resonance means so much more to me than Eigen anything which requires
a university degree to understand. If you are a history buff then I understand
all those references to peoples of the past.
Ill bet [speculatively only] if you could give planet earth a shove into the sun
Then, let it go,
then it might have a resonant frequency as it re stabilizes in
its orbit, Now what would you call such a thing as that ???
Earth Eigen Mode or some kind of resonance for the
Earth/Moon/Sun System. You get a wavelike motion
as the Earth/Moon orbits the Sun.
Mother Nature has done everything man has done
a billion years before man came along.
Why give credit to man any more than the Dollars of pay for his work.
Please, Just call it, "Resonance" Then I don't need to look up anything else.
If you do that,  I will not have to say "Lee De Forest Electron Valve" when talking about a simple Triode vacuum tube.

Although I have heard of Earthquake accelerations in excess of 32F/s^2 which makes two ton boulders hop out of
their places and move quite a good number of feet,  I have never heard of well dampened
soil such as youse-guys have talked about in that recent NZ EQ. It [The Ground ]
seems to have functioned like a giant automobile shock absorber.

Best Regards, 
geoff



--------------------------------------------------
From: "Kay Wyatt" 
Sent: Monday, September 06, 2010 2:26 AM
To: 
Subject: Re: Now I Am Confused - AGAIN

> Mark,
> 
> Can you explain the following sentence from your email...
> 
> "Eigenmode activity was observed sporadically over the week leading up to 
> the
> main quake."
> 
> Sorry for my ignorance.  Thanks muchly!
> 
> Kay
> 
> 
> ----- Original Message ----- 
> From: "Mark Robinson" 
> To: 
> Sent: Sunday, September 05, 2010 3:51 PM
> Subject: Re: Now I Am Confused - AGAIN
> 
> 
>> NZ's geological service has a page up on the quake at
>>
>>> http://www.geonet.org.nz/news/article-sep-4-2010-christchurch-earthquake.html
>>
>> It includes maps and photographs showing the surface rupture which is 
>> variously reported as 13 and 22km in length. Lateral displacements up to 
>> 4m have been measured and are evident in the photographs.
>>
>> The main event report is at
>>
>> http://www.geonet.org.nz/earthquake/quakes/3366146g.html
>>
>> while the following link provides felt reports from the general public as 
>> well as measured peak ground accelerations and velocities
>>
>> http://www.geonet.org.nz/earthquake/quakes/3366146g-shaking.html
>>
>> There have been in excess of 80 significant aftershocks (>mag3) since the 
>> main event and the rest of the country is showing high levels of 
>> background activity with significant volcanic tremor in the volcanic 
>> plateau of the North Island and unusual levels of seismic noise across the 
>> country.
>>
>> Eigenmode activity was observed sporadically over the week leading up to 
>> the main quake.
>>
>> The damage has been compounded by heavy rain and strong winds.
>>
>> The army has been deployed to enforce a cordon around the Christchurch CBD 
>> while isolated disorder is being reported as people try to access 
>> supermarkets and pharmacy services.
>>
>> Official instructions to not attend the hospitals except in cases of 
>> serious emergency leave residents in a Catch-22 as doctors and other small 
>> businesses are instructed not to open until their premises have been 
>> inspected by structural engineers.
>>
>> There is considerable damage to the water and sewerage systems with 20% of 
>> Christchurch having no water supply. This will take a long time to repair.
>>
>> All schools are closed until at least Wednesday.
>>
>> A selection of local media
>>
>> http://www.nzherald.co.nz/?c_id=1502981
>> http://www.scoop.co.nz/
>> http://www.stuff.co.nz/
>> http://tvnz.co.nz/national-news
>> http://www.3news.co.nz/
>> http://www.radionz.co.nz/news
>>
>>
>> On 06/09/10 09:20, GPayton wrote:
>>> Dave, I am so glad that you answered, being from NZ. I was hoping that
>>> you would.
>>> When the quake occurred, I looked at Google Earth and it appeared that
>>> the area was mountainous, but that software can be misleading sometimes.
>>> Thank you for the input. I suspect the ground acted like a "wet sponge"
>>> then.
>>> Best regards,
>>> Jerry
>>>     ----- Original Message -----
>>>     *From:* Dave Nelson 
>>>     *To:* psnlist@.............. 
>>>     *Sent:* Sunday, September 05, 2010 4:04 PM
>>>     *Subject:* Re: Now I Am Confused - AGAIN
>>>
>>>     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 
>>> prepardness...
>>>     very strict building codes etc etc
>>>
>>>     cheers
>>>     Dave Nelson
>>>     Sydney
>>>     Ex New Zealand
>>>
>>>     At 12:21 AM 6/09/2010, you wrote:
>>>      >I was just reading an article about damages from the recent New
>>>     Zealand
>>>      >EQ. I saw the following quote which seemed to be a contradiction
>>>     to the
>>>      >California EQ where soft ground cause liquefaction of the ground.
>>>      >
>>>      >The quote is as follows: "Euan Smith, professor of Geophysics at
>>>     Victoria
>>>      >University, speculated that the very soft soils of Christchurch
>>>     had "acted
>>>      >like a shock absorber over a short period ... doing less damage to
>>>     smaller
>>>      >buildings."
>>>      >
>>>      >Is this just a matter of less water content in the soils?
>>>      >
>>>      >Jerry
>>
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