Webicorder reliability?


In my first post to this blog I noted what appeared to be some exciting readings from the webicorder at station BKE V on Mt. Vesuvius, which appeared to show elevated seismicity at times and at other times seemed to show intense harmonic tremor of the kind one would only expect to see immediately prior to or during an especially violent plinian eruption, and yet there was nothing at all in the media about it, even though 2 million people live around the base of Vesuvius.

There are two web accessible seismographs on Vesuvius, and the other one on the western flank of the volcano showed no such activity, so just what was going on there? It took me some time to figure it out, because writing the seismologists there at Vesuvius got me no responses at all. I guess they don’t care to bother with the public and don’t want to be pestered by we who take an interest in their field of expertise.

What I eventually figured out was that the seismograph stations transmit their readings to radio receivers back at the monitoring station over the air, and what was being picked up as output from BKE V was not it’s output at all, but local radio noise. I wrote their team about this, repeatedly, but again, no response at all from them, and the problem goes merrily on with nothing at all being done about it while we volcanogeeks out here get totally wrong readings from a useless station.

Oh well, at least I was able to figure it out.

More recently I ran into the same thing at Mt. Augustine, which seems to be showing elevated seismicity and harmonic tremor at one station, and again, the second station on the web shows no such activity. At station AUH_EHZ_AV we see this:

Above we see from station AUH_EHZ_AV what might excite us were it real, however when we take a look at the other online webicorder for Augustine we see:

Other than a couple of calibration pulses just about nothing.

Well I wrote the team there at AVO, and unlike their colleagues and contemporaries in Italy they actually wrote me back and confirmed that the readings online for AUH_EHZ_AV were in fact generated by radio noise.

Cheryl Cameron at avo.alaska.gov was kind enough to tell me:

“The Augustine stations are plagued with electronic noise and telemetry issues. (AUI and AUH are particularly bad right now.)

Another problem with seismographs in the Aleutian arc has been wind, especially at the far western end of the arc, at Gareloi, the seismograph there having been subject to strong winds generating vibrations that registered online as apparent seismic activity to those less familiar with seismograms. Cheryl Cameron was again kind enough to verify this for me.

So the point here is that what we are seeing online is sometimes not what’s actually going on with the volcano and cannot always be interpreted as seismic activity. Seismographs are extremely sensitive instruments and pick up vibrations of all kinds from all sources, like vehicular traffic, wind, rockfalls, mining operations, industrial activity, and even animal activity.

And then there is radio noise, which is perhaps the worst issue, and can look like a major eruption in progress if you don’t know what you are looking at. If there is more than one station at the volcano in question you can check one against the other, but if not you are left with whether or not there is publicity online about it, or whether those administering the seismic network are willing to share information with you, which in some cases they are not. Kudos to AVO on this matter.

So folks, when you see something that looks exciting or alarming on a webicorder don’t immediately jump to conclusions and trumpet alarms all over the web and slather it all over abovetopsecret.com claiming the government is covering it up. It might well be nothing at all. Take the time to check it out and know what you are looking at. If you can get an answer back from those administering the seismic network that’s the best way to go.

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About Martina Vaslovik

Volcano nerd and seismogeek
This entry was posted in Uncategorized, Volcanology. Bookmark the permalink.

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