With that said, Steve, I think what you are noticing on the YSB helicorder is a surface response to a geyser or a steam release of some sort. You can note the same captures on the Old Faithful recorder if they ever get it up and running again....lol!
Now as for recordings of true magma flow on the YMR. There were loud bursts of to me what appeared to be harmonics over the last few weeks. When I went back and noticed the times on these type of recording they were remarkably close to the same times on each day. So I have discounted these note on graph at the 17:00 hour as radio transmissions of some sort or vehicular traffic right next to the station.
http://www.quake.utah.edu/helicorder/ymr_webi_5d.htm
However, there have been other responses that make me think indeed we did have harmonics on the YMR. 18:51 period is inclusive of a bona fide harmonic tremor.
http://www.quake.utah.edu/helicorder/ymr_webi_6d.htm
They are not using the YMR as their library recorder, not sure why but the are using one called the Plate Boundary for supposed reduction in noise reasons. However, just like on redoubt, not all recorders were able to pick up the nuances of a Harmonic Tremor and some did not even show a reflection at all.
So that being the case and Layman study of the history is tampered by their choice in webicorders to library.
So if I am learning to read these correctly, there are several instances of harmonic tremors on the ymr recorder between 15 and 1900 today (using the timescale on the left)
Why didn’t you just say they look like fine V tach? ;-)