On 12/13/2012 7:56 AM, chrisatupw@....... wrote:
> From: Tiago A. 
> Sent: Wed, 12 Dec 2012 23:20
> Subject: Missing clear S wave from local event
>
> Some months back i recorded a Ml1.8 event (epicenter at 22km), the P 
> wave is perfectly noticed, but the S wave is somewhat lost.
>
> This is a picture of the earthquake (no filter applied)..i can get the 
> sac file if anyone is interested. A IDA station located more near from 
> the epicenter also have this "issue" in this earthquake, clear P wave, 
> S wave bit lost.
> http://imageshack.us/a/img252/2303/12102012.png
>
> I´ve this video from another event (Ml2.9) near that area, also doesnt 
> have a clear S wave.
> https://www.youtube.com/watch?v=j0P2y2ahDNg
>
> Hi Tiago,
> Two thoughts. The noise level on the .png looks high for a quake only 
> 22 km away. Since you didn't send a digital trace, I can't analyse it 
> / expand the time scale / apply filters for P & S waves of 
> TWOfrequencies. What are the frequencies that you actually see ?
>     Also, the orientation of the slip direction with respect to the 
> observer effects the amplitudes of the waves received. Are you sure 
> that it is the S wave that is missing ?
>     Regards,
>     Chris Chapman
Let me contribute to this discussion. I have two strip mines that are 
active within fifteen miles of my location. It is easy to 
detect/recognize multiple blast occasions but occasionally they do 
single blasts. Usually they occur at specific time of the day. They look 
just like those that Tiago posted. In fact, one occurred last Sunday 
afternoon at about 3 pm local time with rain in the area (not a normal 
situation). As part of a discussion with Memphis, the "event" was 
examined and declared a mine blast. But that is not all that can give 
you such results. There are other events that are not as regular like 
the collapse of bridges, grain storage structures and as is happening 
right now the progressive destruction of a large field house/sports 
arena near me....some large pieces of concrete are allowed to fall. 
Don't neccessarily ignore these events. I detected a small earthquake 
about 9 miles away that was missed by USGS several years ago. Mother 
Nature slips in the real thing once in a while just to keep you alert.

  
    
  
  
    
On 12/13/2012 7:56 AM,
      chrisatupw@....... wrote:

    
    

          

            

              From: Tiago A.
                <tiagoagre@.........>

                
                  
Sent:
                    Wed, 12 Dec 2012 23:20

                    Subject: Missing clear S wave from local event

                    

                    

                      Some months back i recorded a Ml1.8 event
                      (epicenter at 22km), the P wave is perfectly
                      noticed, but the S wave is somewhat lost. 

                      

                      This is a picture of the earthquake (no filter
                      applied)..i can get the sac file if anyone is
                      interested. A IDA station located more near from
                      the epicenter also have this "issue" in this
                      earthquake, clear P wave, S wave bit lost.

                      http://imageshack.us/a/img252/2303/12102012.png

                      

                      I´ve this video from another event (Ml2.9) near
                      that area, also doesnt have a clear S wave.

                      https://www.youtube.com/watch?v=j0P2y2ahDNg

                      

                      Hi Tiago, 

                              Two thoughts. The
                          noise level on the .png looks
                          high for a quake only 22 km
                      away. Since you didn't send a digital trace, I
                      can't analyse it / expand the time scale / apply
                      filters for P & S waves of TWO frequencies. What are the
                          frequencies that you actually see ? 
                      

                          Also, the
                          orientation of the slip direction with respect
                          to the observer effects the amplitudes of the
                          waves received. Are you sure that it is the S
                          wave that is missing ?
                      

                          Regards, 

                              Chris Chapman

                        
                    
                    
                  
                
            
            
          
        
    
    Let me contribute to this discussion. I have two strip mines that
    are active within fifteen miles of my location. It is easy to
    detect/recognize multiple blast occasions but occasionally they do
    single blasts. Usually they occur at specific time of the day. They
    look just like those that Tiago posted. In fact, one occurred last
    Sunday afternoon at about 3 pm local time with rain in the area (not
    a normal situation). As part of a discussion with Memphis, the
    "event" was examined and declared a mine blast. But that is not all
    that can give you such results. There are other events that are not
    as regular like the collapse of bridges, grain storage structures
    and as is happening right now the progressive destruction of a large
    field house/sports arena near me....some large pieces of concrete
    are allowed to fall. Don't neccessarily ignore these events. I
    detected a small earthquake about 9 miles away that was missed by
    USGS several years ago. Mother Nature slips in the real thing once
    in a while just to keep you alert.