Andy, Beverly

There was an interesting event pointed out by Corey in alog 37882. Beverly identified it as a 1.9 earthquake at 60 km from the site. At that distance, the higher frequencies (a few Hz) had a big effect, and caused a lot of noise in DARM very similar to the blue mountains noise. It seems like this motion rang up a baffle with a very long damping time, so maybe it'll give us some new information about how ground motion couples to the baffles.

The first plot shows the earthquake in the HAM2 seismometer. It lasts about 60 seconds. The second plot shows how IMC_F is affected - it has a lot of scattering during the quake, but that only lasts during the earthquake. The effect in DARM (third plot) lasts much longer. It seems like the ground motion ends around 75 seconds into the plot, after which it takes more than 60 seconds for the scattering to die down by a factor of 2.

The fourth plot shows that the IMC has fairly regular scattering arches coming from a motion with a frequency around 2.5 Hz. We should be able to confirm that one of the resonances of the MC mirrors is rung up.

The last two plots are a comparison of the start of the motion in IMC and DARM. IMC seems to respond immediately, while it seems that the baffle takes some time to build up enough motion to make scatter that shows up in DARM. The observed damping time doesn't seem to match the Swiss cheese baffle either before or after the damping, though this needs further checking. Is this something else getting rung up?