PSN-L Email List Message

Subject: Re: Missing clear S wave from local event
From: Dave Nelson dave.nelson@...............
Date: Sun, 16 Dec 2012 08:16:00 +1100



Dunno about anyone else but I cannot open your .sac files
WinQuake refuses to look at it  ??
can you not save them as standard Winquake files ?

Dave


At 03:32 PM 15/12/2012 -0100, you wrote:
>Hi.
>
>Sorry for the late reply.
>
>The sensor is a L4 1Hz, i do have a noisy system due to several factors=20
>(some already discussed here in PSN Listing Mail).
>
>Here is the SAC file of the event:
>http://dl.dropbox.com/u/15=
802004/12_10_2012.sac
>
>This the SAC file of the IDA station located +-10km of the event (much=20
>better recording than mine).
>http://dl.dropbox.com=
/u/15802004/cmla_12_10_2012.sac
>
>I do not know if this is a "natural" event, while i do receive some=20
>"blasts" every month, at 4am i dont believe to be a blast.This event is=20
>located near a dormat volcano, that 10 years back had high seismic crisis.=
=20
>Some believe that the geothermal exploration on that system turned the=20
>system a bit unstable ( coincidence when they started the exploration back=
=20
>in the 80s, the area had a big seismic crisis). This event was classified=
=20
>with Ml1.8, 5km depth.
>
>So the hypothesis are:
>-Only S wave was recorded, P wave is missed between the noise.
>-Only P wave is clearly recorded.
>-Due to short distance to the epicenter, P and S waves are mixed together.
>
>But except this event and 1/2 more, i can always understand if a P is=20
>recorded or not. Comparing my SAC file with the CMLA IDA station, what do=
=20
>you think?
>
>Best Regards,
>Tiago.
>
>
>
>
>
>2012/12/13 Bob Hancock <raptor@.......>
>One other thought, the peak amplitudes of the P & S waves are 90 degrees=20
>out of phase.  Also the classification of the focal mechanism of the event=
=20
>could have contributed to one wave being much more visible than the other=
=20
>wave.
>
>The amplitude of body waves such as the P & S waves, are dependent upon=20
>the focal mechanism of the event.
>
>Another factor is the sensitivity range or band width of your=20
>receiver.  If it is either a high frequency receiver or of minimal band=20
>width, you could see the P wave and the S wave would not be visible,=20
>whereas with a broader band receiver both waves would be visible.
>
>Your email does not define the scale at the bottom of the chart, minutes=20
>or seconds, but in either case no surface waves are visible.  Again this=20
>could be related to the frequency range of your receiver.
>Bob Hancock
>
>On Dec 12, 2012, at 4:20 PM, Tiago A.=20
><tiagoagre@.........> wrote:
>
>>Hi.
>>
>>Some months back i recorded a Ml1.8 event (epicenter at 22km), the P wave=
=20
>>is perfectly noticed, but the S wave is somewhat lost.
>>
>>This is a picture of the earthquake (no filter applied)..i can get the=20
>>sac file if anyone is interested. A IDA station located more near from=20
>>the epicenter also have this "issue" in this earthquake, clear P wave, S=
=20
>>wave bit lost.
>>http://imageshack.us/a/im=
g252/2303/12102012.png
>>
>>I=B4ve this video from another event (Ml2.9) near that area, also doesnt=
=20
>>have a clear S wave.
>>https://www.youtube.com/wat=
ch?v=3Dj0P2y2ahDNg
>>
>>In the Ml1.8 event the lack of a clear S Wave is more evident, what=20
>>happened to the S wave? This events occured near a volcanic region, but=20
>>i=B4ve recorded earthquakes from other volcanic regions, and i have always=
=20
>>a clear P, S wave.
>>
>>I apreciate any thought on this.
>>
>>Regards,
>>Tiago.


Dunno about anyone else but I cannot open your .sac files
WinQuake refuses to look at it  ??
can you not save them as standard Winquake files ?

Dave


At 03:32 PM 15/12/2012 -0100, you wrote:
Hi.

Sorry for the late reply.

The sensor is a L4 1Hz, i do have a noisy system due to several factors (some already discussed here in PSN Listing Mail).

Here is the SAC file of the event:
http://dl.dropbox.= com/u/15802004/12_10_2012.sac

This the SAC file of the IDA station located +-10km of the event (much better recording than mine).
http://dl.dro= pbox.com/u/15802004/cmla_12_10_2012.sac

I do not know if this is a "natural" event, while i do receive some "blasts" every month, at 4am i dont believe to be a blast.This event is located near a dormat volcano, that 10 years back had high seismic crisis. Some believe that the geothermal exploration on that system turned the system a bit unstable ( coincidence when they started the exploration back in the 80s, the area had a big seismic crisis). This event was classified with Ml1.8, 5km depth.

So the hypothesis are:
-Only S wave was recorded, P wave is missed between the noise.
-Only P wave is clearly recorded.
-Due to short distance to the epicenter, P and S waves are mixed together.

But except this event and 1/2 more, i can always understand if a P is recorded or not. Comparing my SAC file with the CMLA IDA station, what do you think?

Best Regards,
Tiago.





2012/12/13 Bob Hancock <raptor@.......>
One other thought, the peak amplitudes of the P & S waves are 90 degrees out of phase.  Also the classification of the focal mechanism of the event could have contributed to one wave being much more visible than the other wave. 

The amplitude of body waves such as the P & S waves, are dependent upon the focal mechanism of the event.

Another factor is the sensitivity range or band width of your receiver.  If it is either a high frequency receiver or of minimal band width, you could see the P wave and the S wave would not be visible, whereas with a broader band receiver both waves would be visible. 

Your email does not define the scale at the bottom of the chart, minutes or seconds, but in either case no surface waves are visible.  Again this could be related to the frequency range of your receiver.
Bob Hancock

On Dec 12, 2012, at 4:20 PM, Tiago A. <tiagoagre@.........> wrote:

Hi.

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=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

In the Ml1.8 event the lack of a clear S Wave is more evident, what happened to the S wave? This events occured near a volcanic region, but i=B4ve recorded earthquakes from other volcanic regions, and i have always a clear P, S wave.

I apreciate any thought on this.

Regards,
Tiago.

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