Homestake Meeting Minutes, 12/08/17

Attending: Andrew, Jan, Pat, Ross, Vuk, Daniel, Michael, Gary

Agenda:

• Next Meeting: Jan 12?
• Data analysis topics
  • Data corrections, frame production (Gary/Daniel/Pat)
  • Event catalog (Gary/Ross)
  • Radiometer updates (Pat, Andrew)
  • Parameter estimation for Rayleigh and Love (Pat)
  • Teleseismic events and Wiener filtering (Daniel, Michael)
  • Very-long-periods (Ross)
  • Velocity from noise correlations (Daniel)
    • Model selection?
  • Pull together all velocity measurements to start making comparisons (all)

• Papers
  • Homestake Array Summary paper:
    • Leads: Vuk, Gary, Victor
    • Submitted to Seism. Research Lett.

• Active excitation overview paper
  • Leads: Gary, Ross
  • Others: Victor, Daniel,…
  • Draft of the paper exists, as a report for IRIS. Gary will be adopting it to a publication. Don't have a particular date in mind.
  • Vuk: Gary reports via email that he expects to be working on this paper over the holiday break.

• Surface Active Excitation
  • Leads: Victor, Boise
  • Others: Gary, Ross
  • Plan to invite the Boise group to give us a presentation in Sep or Oct 2017, when they are ready with their paper.

• Underground Active Excitation:
  • Lead: Gary, Ross

• Parameter estimation for the Rayleigh and Love eigenfunctions (amplitude vs depth dependence).
  • Leads: Pat, Daniel
  • Also contributing: Victor, Vuk, Levi

• Estimating directional and modal composition of the seismic noise. (Pat, Levi, Vuk)
  • Leads: Pat, Vuk, Levi

• Wiener filter application
  • Leads: Jan, Michael
  • Latest version: wiener.pdf. Needs minor modifications of figure 6, and still need to rewrite conclusions.
  • Vuk: Why can't you measure seismic speed below 1.2 Hz.
  • Jan: Not clear, the method should work, it looks like there is a lot of variability around 1Hz, potentially different wave modes.
  • New point in the paper: evidence of the presence of body waves at 0.2 Hz, based on the speed measurement. Body waves seem to dominate on some days. In fact, it seems there is a continuous body wave background and on some weeks a stronger Rayleigh background overcomes it. Important for GW detectors.
  • Vuk: suggest to emphasize this to Victor and Gary via email, their response could help place this result in existing geo literature. ALso suggest to plot Fig 6 as a scatter plot, which should appear as -45 degree line.
  • Daniel: where would body waves come from?
  • Jan: not sure.
  • Jan: also have very good Wiener subtraction. Should we try a more visible journal, like Nature geophysics?
  • Vuk: worth considering, depends on what is known about body vs Rayleigh background. Also, it seems we don't need the depth aspect of this array is not needed for Fig 6.
  • Jan: correct, could try another array like Sweatwater.
  • Vuk: Could we use an estimate of Rayleigh wave speed from elsewhere? And plot lambda/4 on the Figure 5.
  • Ross/Pat: could try to estimate the speed from mining blast data. Pat working on this now, Ross did a study in the past.
  • Jan: Could use shear wave speed, which was measured, and convert based on some assumption on the poisson ratio. This could be a value for now, that could be updated later from other analyses.
  • Gary: could use the mine blasts. Have very solid data on shear wave speed from the active excitation at 2000. But this is on the scale 10-100m, but don't know it at a larger scale, but wouldn't expect it to very much. You can also get uncertainty on these velocity measurements.
  • Jan will send an email summarizing these results. We should discuss how to proceed via email, if necessary we'll schedule another call before the winter break…

• Teleseismic EQs and near-surface scattering
  • Leads: Daniel, Victor

• Time-variable velocity changes
  • Lead: Victor, not started yet

• Very low frequency harmonics (Ross)