corey.gray@LIGO.ORG - posted 15:53, Thursday 01 December 2016 - last comment - 09:53, Friday 02 December 2016(32084)
Earthquake Report: 6.3, Peru, H1 Lockloss
- Magnitude of EQ (according to Terramon): 6.3
- Location of EQ (according to Terramon): 43km NE of Huarichancara, Peru
- Starting time of Event: 22:49UTC (started seeing 0.03-0.1 BLRMS increase
- Lock Status: H1 Lockloss at 23:25UTC
Corey, Sheila, Jim W
TerraMon and LLO warned Corey that this EQ was coming, with a predicted R wave velocity of 4.8 um/second (it showed up in our EQ band BLRMS peak at about 1 um/second RMS at about the time predicted). Our useims blrms is around 0.3-0.4 um/second right now.
Since Corey had a warning he consulted with Jim W who suggested trying BLEND_QUIET_250_SC_EQ for both end station ISIs (one at a time). The attached screenshot shows the transition from BLEND_QUIET_250_SC_EQ back to our normal windy configuration BLEND_QUIET_250_SC_BRS, which is much quieter at 50-70 mHz.
Jim explans that this sensor correction has a notch at around 50mHz (he will attach a plot), and that this worked OK durring the summer when the microseism was verry low. However, it will reduce the amount of isolation that we get at the microseism, which was fine when Jim first tested it in the summer months.
If an EQ moves the whole site in common, we can lock all the chambers to the ground at EQ frequencies to reduce the common motion. Our problem this time was probably that we switched only the end stations without changing the corner.
For now, the recomeneded operator action durring earthquakes is:
If the IFO is locked, don't do anything. We want to collect some data about what size EQ we can ride out with our normal WINDY configuration.
If the IFO unlocks, and the earthquake is going to be large enough to trip ISIs (several um/sec) switch the ISI configuration node to LARGE_EQ_NOBRSXY. This just prevents tripping of ISIs
Once the BLRMS are back to around 1 um/sec you can set the SEI_CONF back to WINDY, and ask ISC_LOCK to try LOCKING_ARMS_GREEN. If the arms stay locked for a miute or so, you can try relocking the IFO.