Link to all those helicorders is
here
I see what you mean, OP. They are really messy looking traces. We see stuff like that on some of the Yellowstone ones too at times, and in some other
places as well. In the case of Yellowstone we referred to them as going "Pollock" because they look like Jackson Pollock paintings.
The cause? Generally, where the helicorder traces are all over the place all day like that but there is not actually any notable seismic activity
going on -- and we'd sure hear about it if there was -- it typically is the result of wind effects. Yes, wind can affect the helicorders, especially
if there are trees nearby. This is because the wind moves the trees and that, in turn, causes movements in the tree roots. These movements get picked
up as vibrations through the ground and make it look like major quakes going on for hours and hours, even when it's obvious there aren't.
If the traces go crazy only during normal working hours (at a given location), it's often "cultural noise", meaning things like snow ploughs and snow
grooming machines if the area is under heavy snow. Or sometimes just heavy traffic. A couple of the LA seismos show very clear increases in activity
when it's busiest on the nearby main roads. They can also be affected by portable generators that are used to supply power to some seismo stations,
but these tend to have a pretty distinctive pattern as they cut in for a short while to charge the batteries then shut down again. So what you're
seeing there is not typical for generator interference.
These crazy traces cover almost the whole day in some cases, so I'd go for wind being the culprit here rather than just cultural noise. You'll find
there are several other days that show very similar traces, besides the specific dates you mentioned.
Fortunately the people who watch these things for a living are well aware of the things that can disturb the helis and they allow for this. Where the
things get swamped, they'll check others within the general region and study those that are less affected by weather factors or cultural noise.
Some seismos, even well inland, can also get affected by ocean waves pounding the beaches, even many miles away. But again, that has a fairly
distinctive pattern, not like the (probable) wind effects we're seeng on those helis.
edit on 20/3/13 by JustMike because: (no reason
given)