PSN-L Email List Message

Subject: Re: Detecting micro-earthquakes
From: Roger Sparks rsparks@..........
Date: Thu, 09 Feb 2006 17:27:00 -0800

Hi All, 

Hi Jon,

I took a look at your files.   Thanks for making them available.

While I have become familiar with my own seismometer and capabilities, I 
am looking at a different world when looking at your files.   First is 
the 200 samples per second which provides resolution of events as high 
as 100 Hz.    That is very good.

Next is the 4.5 Hz geophone which has a peak response at about 4.5 Hz.   
I expect  it to detect local quakes very well.   The expectations for 
large distant quakes are less.

What surprised me was the large amount of energy found at 10 Hz, 
declining up to about 20 Hz.   I did not expect to see that when I 
applied the FFT algorithm from Winquake to each file, and for the most 
part, to each subdivided time period within each file.   What I expected 
to see was the ocean wave noise at 0.2 Hz but at a much reduced peak 
compared to my own seismometer which has a natural period of about 3 1/5 
to 4 seconds.   I am curious to know if you can explain the 10 Hz energy 
source?   Also ocean waves?  Maybe a nearby flag pole and flag waving in 
the wind?

The second surprise was the large noise count, up in the +/- 300 unit  
range.   It is nothing to be alarmed about, only different from my 
system.   I wonder what the noise floor is when the seismometer is 
disconnected from the electronics?

After looking at the files, the trace that most looked like a quake to 
me, occurred at about 36:11.    I have a lot of local (people walking) 
quakes and occasionally see a trace like the 36:11 trace that is not a 
quake, so I would not go so far as to say it was one.   I always check 
to see if other stations have also recorded the event before having 
confidence in my own results.

It takes a while to learn the capabilities and limits of new equipment.  

Best wishes,  Roger

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>| Message 2                                                           |
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>Subject: Re: Detecting micro-earthquakes
>From:    =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= 
>Date:    Mon, 06 Feb 2006 17:54:03 +0000
>Hi all
>To Roger.
>I have 4.5Hz geophone, becose of that i don't detect the ocen wave most
>of the time (maybe during storm). 
>Other matter.
>I think that i might have recorded a small earthquake, but there was a
>mining expotion at distance of 119km away from me around the same time,
>that i might have been able to pickup. However the p and s wave are so
>close to gether that i doubt that i was recording the mining explotion
>as i did first think, becose if i apply that timeing of the subspected
>mining, the p and s wave are behind the top that i see. There is a other
>option regarding this, this event might have been created when the earth
>freezes over and it cracks when that happens. But the current temp is
>-3.5C and the ground is freezing over. This might also just be noise.
>Here are the files for those intrested.
>Thanks and regards. (sorry for spelling errors)

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