Robert, Tony

My beating shaker data from Thursday commissioning was ruined by large scattering glitches in DARM. We also saw these glitches on Friday. I found that they were coincident with brief seismic and microphone signals (Figure 1). The coupling site has to be EX because the signals appear in DARM before they reach any other station (Figure 2). I was able to determine that they could be coming from the direction of one crater-marked site on the east side of YTC, but not a more central location that Tony and I had found. The propagation velocity of the 5-20Hz signal is the same for both seismic and acoustic sensors and about 337 m/s indicating that the dominant propagation is through the air not the ground, though it couples to the ground locally. The linear attenuation in the ground at these frequencies is much greater than it is in the air.

The scattering noise produced at EX in DARM has harmonics of about 10 Hz (Figure 1, page 2). This is about the frequency of one of the worst resonances of the cryobaffles (9.7 Hz here: 56857 ). This is a reminder that we did not reduce the light reflected back into the interferometer from the cryobaffles, we just reduced their usual velocity by damping them. The explosions apparently kick the EX one pretty hard. It would be interesting if Detchar could keep track of the YTC glitches and also see if they ever knock us out of lock.