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: {{:groups:homestake:meetings: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)