I play about with creating sound files from earthquake waveform files. I do it quite a lot actually and I have got used to being able to identify events from the sounds rather than the image of the seismogram.
Now I have no doubt a seasoned seismologist would take a look at the seismogram below and give you an instant answer as to what was causing it. This was the one I was asked to take a look at as the person asking was concerned about volcanic activity. (All seismogram images in this post were provided by IRIS and are (C) University of Washington Seismic Network)
Not being a seasoned seismologist, well let’s be honest not being a seismologist, my initial thoughts were not earthquake related, not volcanic even though this site is near Mount Baker.
There are many and varied patterns of interference that can be seen on seismograms from telemetry errors, to solar influences, generators, irrigation machinery, even the heaters on the seismographs themselves. I will dig out a few examples of these sometime and post them.
Ordinal day 150 was a Monday (May 30th) (very useful ordinal date calculator) The pattern at the bottom of the seismogram is very reminiscent of cultural noise, mainly because of it’s sharp onset and consistent signal.
Bear with me and look at these:
From those 4 you might be seeing a pattern, not in the furry lines but in the cultural noise starting at 1300 hrs and finishing around 2300 hrs. Clear on Monday and Friday, not so clear on Saturday and pretty much absent on Sunday.
This animated GIF shows the picture more clearly. It runs from Saturday through to Monday – SSMTWTFSSM – so you can clearly see the cultural noise. 1300 hrs – 7hrs is 0600 hrs, and it finishes around 2300 hrs – 7 which is 1600 hrs. Note that the first Saturday it goes on much longer.
So where is PAYL? Answer it is at a school. This probably explains the fixed times of the cultural noise adequately, so what about the furry things?
12 Jun 2013: Unfortunately since I wrote this post in 2011 the sound files appear to have been lost but I do still have a FLAC file of the sound. This is the 100 samples per second (Hz) HHZ channel played at 2000 sps, so 20 x speed. FLAC files can be played with WinAmp (free) if your current audio player does not play them.
Listen, and you hear a sound approaching passing and then fading away. This has to be either road traffic, or aircraft, or trains.
Is there a railway near the school?
There is indeed! (Actually I did not measure the shortest distance as you can see.)
That Saturday one showing there may have been a ‘do’ on at the school on the Friday evening which finished at or just before 10pm local time.