The seismograph on the north west flank of Shastina consistently show activity like this, over 24 hours. I wanted a pro to clue me in as to their significance, if any. Here's what I see and what she said.
These seismic records look like harmonic tremor or low-frequency volcanic tremor, normal volcanic activity associated with normal fluid (magma) migration.
"Harmonic tremor, or volcanic tremor, is the name for the continuous, rhythmic seismic energy associated with underground magma movement."
They are likely originating from Shasta, since the two stations you picked are the closest to Shasta. The smaller "heartbeat" like pulses are likely also associated with fluid movement which can get "stuck" as it moves through the volcanic plumbing and causes these shorter, spikier events (akin to water moving through your ear canals after swimming, you hear short jumpy sounds!).
I think the red is indicating that the seismometer is reaching the edge of its dynamic range and is thus just recording the maximum amplitude.
I am, however, not a volcano seismologists (i'm an EQ seismologist!) so I do not do regular volcanic monitoring and am not up on the current activity at Shasta.
Under ground magma movement does not make me feel more secure. Sooner or later it might find a way to the surface, and then....