reply to post by AuntB
OK LA09 looks like the pumps/venting and the normal traffic. Nothing strange on that one.
LA03 however is odd. Two signature are curious and in many respects identical. They are symmetrical and definitely not earthquakes. At this time I am
having a problem identifying what they might be. I will get back to you on that.
This is the trace directly from the SAC file for all three channels for the event ~19:45
First of all let me say I do not believe it is seismic as in earthquake. The next question is could it be collapse of walls in the sink hole. No I do
not believe it is mainly because there are two virtually identical signals and for that to happen in a pit wall collapse would be odd to say the
This is the spectrogram of the three channels.
The next problem is that IF this was a wall collapse there would not be the pattern that you see there. It would be progressive. I also suspect that
it would be much quicker than 8 minutes of more that this sequence takes. * minutes however excludes traffic for these two events.
We were talking about venting earlier. Could this be venting.? That would explain the symmetrical pattern and the length of time.
One other point the signal is 'bent' as you can see on the first traces. This only happens to the E and N channels and not to the Z channel which is
odd except that (and here I cannot swear by this) the electronics of the seismo for those two elements would be in the same plane but at 90 degrees to
each other I would imagine. If they are in the same plane they could be affected by a signal that did not affect the Z channel which would be in a
plane at 90 degrees to them and possibly shielded by it's casing. Just my thoughts out aloud on that.
I have seen similar, but not identical, signals where seismos are sited in sub stations or by generators (yes it happens) and are affected by the
electrical fields. The latter part of the signal has the sharp look of a seismic signal but bear in mind that this signal is ONLY seen on LA03 and
that 100% makes it something specific to that instrument.
I have to be honest and say that I cannot definitely pinpoint what this is for these two signals. I am still playing with the sound files so if I come
up with anything I will let you know.
ETA: Have a listen for yourselves
. 92Kb flac file.
edit on 27/11/2012 by PuterMan because: part of the comment removed as it brought nothing to the discussion.