Actually, Godzilla not to get in this fight but....lol Yeh, right, sure ;)
I can see (given the quality of the image)I see what could be harmonics beginning at about 14:45 and continuing to about 17:19 with increasing sharp, short seisimic events superimposed.
The following makes a comparison between common seismic forms
Now the issue is whether or not the seismographs at Ystone are seeing magma moving or only tectonic quakes (or the very similar shallow volcanic quakes - both involve rock movement) - the evidence points to tectonics. With all the study of harmonic tremors since Mt. St. Helens, this is one wave form that would get the notice of the seismologists.
All that out of the way?...lol
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.