Effects of light earthquakes on land detectors

Edson Souza
Edson Souza
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Topic 192656

Does anybody knows how people from LIGO or GEO elliminate the influence of shakes on the land from the actual data measured from gravitational waves from the Sky ? An how much of this interference remains in the data filtered ?

Chipper Q
Chipper Q
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Effects of light earthquakes on land detectors

Quote:
Does anybody knows how people from LIGO or GEO elliminate the influence of shakes on the land from the actual data measured from gravitational waves from the Sky ?

It can't be completely eliminated: the alignment of the interferometers is so sensitive that earthquakes in other parts of the world can actually cause the interferometers to loose their lock, and drop out of 'Science Mode', and no data can be collected at all during these events. That's not all: things like trucks and trains are troublesome, too. The sound from a helicopter's blades (or an airplane's prop) beating the air, have an effect on the operation of the interferometers when one flies nearby. Lots of very sophisticated, specialized equipment is required to 'isolate' as much as is possible, the mirrors and optics used in the interferometers, from the many types of seismic vibrations, and other kinds of noise.

Quote:
An how much of this interference remains in the data filtered ?


Hopefully, almost none of it; the scientists tag the data during the times when things like a vehicle is being driven on the grounds, or people are working near sensitive areas while the interferometer is operating in 'Science Mode'. Using interferometers in different locations is also a big help to identify and eliminate a source of local noise at one observatory (and not at the others). The interferometers undergo thorough testing during the calibration runs, and continued testing during normal operation, to assure that they're operating at the level of sensitivity for which they were designed.

Odysseus
Odysseus
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Just chiming in to recommend

Just chiming in to recommend that you check out the “Detector Watch� threads in this forum; there’s a lot there concerning “detector lock�, including interesting graphics galore. (Dialup users beware.)

Ben Owen
Ben Owen
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Edson, I seem to recall

Edson,

I seem to recall anything over 5.5 on the Richter scale anywhere in the world would knock us out. But I haven't been in the control room in a long time; it may be better now.

Then there's microseism: This is a constant background of noise below the frequency band of the detector. So we don't see it directly in the noise curve, though some of it can upconvert into the band. Mainly it's an "environmental" effect - on a bad day (high microseism) the interferometers are squirrelly and drop out a lot. Sometimes we'd reduce the laser power to stabilize at the cost of sensitivity. And on a bad microseism day it could take ages to get back into science mode after every dropout. A lot of that noise comes from waves hitting the beach hundreds of miles away (at least in Hanford which is the only place I've done shifts), so if it's been stormy we know we're in for a rough time.

You can see local traffic too in some bands (a few Hz, if I remember right). There's definitely a rise in the ambient noise during working hours, and it's quieter on holidays. Very rarely you get a big spike that's attributable to a specific (big, nearby) vehicle, and sometimes lose lock from those.

I'll say something related in the "Alternative sources of GW" thread shortly.

Hope this helps,

Ben

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