PSN-L Email List Message

Subject: Re: What is an earthquake?
From: Thomas Dick dickthomas01@.............
Date: Sat, 19 May 2012 13:01:37 -0500


On 5/19/2012 11:14 AM, Brett Nordgren wrote:
> Thomas,
>
> No problem.
>
> First thing I looked at was what amount of energy would go into the 
> earth in the pumping process.  Using an extreme case of 1.1E7 liters 
> at 100MPa pressure gives 1.1E6 Joules.  More typical values, I 
> suspect, are at least 10x less.  If all that energy, 1.1 MegaJoules, 
> could somehow be released as a quake, it would still be significantly 
> below 'magnitude' 1.0, more typically much below.  For quakes larger 
> than that, it implies that the energy was already there, apparently 
> stored as strain in the rocks and that the quakes are probably just 
> being triggered.
> *Disregard using pressure;**just a column of liquid several 1000ft in 
> height has pressure itself* *---even if there isn't any "chemicals" in 
> it. They claim to be considering putting carbon dioxide in salt water 
> reservoirs to reduce carbon emissions at electrical generating 
> plants....I can't believe under pressure acids wouldn't develop that 
> dissolve rock and even produce gases.  And I am told wells as deep as 
> 15000ft will be drilled in the next five years. Gad, I sound like an 
> environemtalist ... I am far from that!*
> For one discussion of mid-continent Intraplate Triggered Quakes see 
> BSSA October 2003 v. 93 no. 5 p. 2212-2221  in which the author 
> presents evidence that the big New Madrid quakes and the Charleston 
> quake may have been triggers for a number of quakes in the Midwest on 
> previously unknown faults.

*Yes*
> My suspicion is that there often are stresses on unknown, dormant 
> faults which in the normal course of things might never rupture, but 
> which can and do when they are helped along.
*The geological history of Arkansas and Missouri* *supposedly had this 
area as a series of volcanic islands in a shallow sea*.

*When the "earthquakes" started in Arkansas, a USGS scientist suggested 
the possibility that there was a fault system longer than the San 
Andreas starting In Arkansas and extending at right angles through the 
New Madrid system all the way across Kentucky and ending in the 
Knoxville area*
>
> I'm not arguing that these are naturally occurring quakes, just that 
> their shake energy comes from the same source as ordinary ones.  They 
> would almost certainly not occur naturally, at least not for a very 
> long time, if they weren't triggered by pumping water into them.
> *But, if you are right, wouldn't the same phases be displayed as for a 
> "normal" earthquake.*
> To really understand what's happening would probably require a good 
> number of short-period instruments planted nearby.
> *That brings up another subject; did you see during a recent seminar 
> (podcast) at the USGS Menlo Park the speaker claimed that some 
> teleseimic earthquakes give off strong energies in the 1-2 Hz range? I 
> had noticed that occasionally I get good copy on distant earthquakes 
> on my 4.5 Hz geophones that I couldn't understand. This happened this 
> morning in the Chile quake.*
> Brett
>
> At 09:35 AM 5/19/2012, you wrote:
>>> 
>> Brett,
>>  Your opinion is logical. But....at least two "quakes" listed as 
>> occuring in Indiana this month are not on faults. The Timpson quake 
>> was described as "poor" in quality. Who/what is studying such 
>> earthquakes? What can be gained from the data where much of the wave 
>> phases are missing or distorted?  Of the last ten quakes listed (at 
>> the present) for the middle states on Memphis website, only three 
>> are(more likely) naturally occurring quakes. I am not wanting to 
>> appear belligerent sounding.  I am raising the question not in an 
>> argumentative way but trying to understand the scientific value.
>> __________________________________________________________
>
>
> __________________________________________________________
>
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>


  
    
  
  
    On 5/19/2012 11:14 AM, Brett Nordgren wrote:
    
Thomas,

No problem.

First thing I looked at was what amount of energy would go into the earth in the pumping process.  Using an extreme case of 1.1E7 liters at 100MPa pressure gives 1.1E6 Joules.  More typical values, I suspect, are at least 10x less.  If all that energy, 1.1 MegaJoules, could somehow be released as a quake, it would still be significantly below 'magnitude' 1.0, more typically much below.  For quakes larger than that, it implies that the energy was already there, apparently stored as strain in the rocks and that the quakes are probably just being triggered.
Disregard using pressure; just a column of liquid several 1000ft in height has pressure itself ---even if there isn't any "chemicals" in it. They claim to be considering putting carbon dioxide in salt water reservoirs to reduce carbon emissions at electrical generating plants....I can't believe under pressure acids wouldn't develop that dissolve rock and even produce gases.  And I am told wells as deep as 15000ft will be drilled in the next five years. Gad, I sound like an environemtalist ... I am far from that!
For one discussion of mid-continent Intraplate Triggered Quakes see BSSA October 2003 v. 93 no. 5 p. 2212-2221  in which the author presents evidence that the big New Madrid quakes and the Charleston quake may have been triggers for a number of quakes in the Midwest on previously unknown faults.

Yes
My suspicion is that there often are stresses on unknown, dormant faults which in the normal course of things might never rupture, but which can and do when they are helped along.
The geological history of Arkansas and Missouri supposedly had this area as a series of volcanic islands in a shallow sea.

When the "earthquakes" started in Arkansas, a USGS scientist suggested the possibility that there was a fault system longer than the San Andreas starting In Arkansas and extending at right angles through the New Madrid system all the way across Kentucky and ending in the Knoxville area

I'm not arguing that these are naturally occurring quakes, just that their shake energy comes from the same source as ordinary ones.  They would almost certainly not occur naturally, at least not for a very long time, if they weren't triggered by pumping water into them.
But, if you are right, wouldn't the same phases be displayed as for a "normal" earthquake.
To really understand what's happening would probably require a good number of short-period instruments planted nearby.
That brings up another subject; did you see during a recent seminar (podcast) at the USGS Menlo Park the speaker claimed that some teleseimic earthquakes give off strong energies in the 1-2 Hz range? I had noticed that occasionally I get good copy on distant earthquakes on my 4.5 Hz geophones that I couldn't understand. This happened this morning in the Chile quake.
Brett

At 09:35 AM 5/19/2012, you wrote:
<clip>
Brett,
 Your opinion is logical. But....at least two "quakes" listed as occuring in Indiana this month are not on faults. The Timpson quake was described as "poor" in quality. Who/what is studying such earthquakes? What can be gained from the data where much of the wave phases are missing or distorted?  Of the last ten quakes listed (at the present) for the middle states on Memphis website, only three are(more likely) naturally occurring quakes. I am not wanting to appear belligerent sounding.  I am raising the question not in an argumentative way but trying to understand the scientific value.
__________________________________________________________


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