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 i=
s perfectly noticed, but the S wave is somewhat lost.=20

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 epic=
enter also have this "issue" in this earthquake, clear P wave, S wave bit l=
ost.
http://imageshack.us/a/img252/2303/12102012.png

I=C2=B4ve this video from another event (Ml2.9) near that area, also doesnt=
 have a clear S wave.
https://www.youtube.com/watch?v=3Dj0P2y2ahDNg

Hi Tiago,=20
    Two thoughts. The noise level on the .png looks high for a quake only 2=
2 km away. Since you didn't send a digital trace, I can't analyse it / expa=
nd the time scale / apply filters for P & S waves of TWO frequencies. What =
are the frequencies that you actually see ? =20
    Also, the orientation of the slip direction with respect to the observe=
r effects the amplitudes of the waves received. Are you sure that it is the=
 S wave that is missing ?=20
    Regards,=20
    Chris Chapman

=20
=20







From: Tiago A. <tiagoagr=
e@.........>






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 i=
s 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 epic=
enter also have this "issue" in this earthquake, clear P wave, S wave bit l=
ost.





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









I=C2=B4ve this video from another event (Ml2.9) near that area, also doesnt=
 have a clear S wave.




https://www.youtube.com/watch?v=3Dj0P2y2ahDNg










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 / ex=
pand the time scale / apply filters for P & S waves of TWO frequencies. What are the frequencies that you ac=
tually see ?  



    Also, the orientat=
ion of the slip direction with respect to the observer effects the amplitud=
es of the waves received. Are you sure that it is the S wave that is missing ? 



    Regards, 



    Chris Chapman