Homestake Meeting Minutes, 07/27/17

Attending: Pat, Andrew, Daniel, Ross, Victor, Vuk

Agenda:

• Next Meeting: Aug 24.
• Data analysis topics
  • Data corrections, frame production (Gary/Daniel/Pat)
    • Pat: Frames ready at Caltech.
    • Daniel: Some timing hiccups, especially when a station is reset, timing off by 1/4 of a second. Have to chase it further, may be ignorable. Doesn't happen often. We could flag the times/stations when this happens. (See also below)
    • Don't know if IRIS updated the data yet, should check with Gary…
  • Event catalog (Gary/Ross)
  • Radiometer updates (Pat, Andrew)
  • Parameter estimation for Rayleigh and Love (Pat) - pdf
    • Velocity estimate is close to the local phase velocity, estimated using local displacements as a function of depth.
    • Homogeneous half-space is not a good approximation, don't get good fits to the depth data.
    • H/V ~ 1.3 - Victor: this is normal/common.
  • Teleseismic events and Wiener filtering (Daniel, Michael)
    • Vuk: making progress, will try to present at the next meeting.
  • Very-long-periods (Ross) - pdf, pptx
    • Putting a paper together. Large section written up. Expect to circulate it in a month or so.
    • Next try to remove tides alone, see how that affects the data.
  • Velocity from noise correlations (Daniel): pdf
    • see timing glitches at some times.
    • Pat: seems to be related to bad timing, maybe due to network problems.
    • Ross: may be an issue with the 800 station, had a large number of mass re-centerings.
    • Daniel: Also see slow drifts in RRDG, know that we lost the clock in this station towards the end of the run.
    • Find time-shift between two stations to match the waveforms, this gives the group velocity. Do it for each station pair individually, works well for some cases and not for others.
      • Similar to Pat's analysis, but using the noise instead of transients.
    • Concern regarding uncertainty for station pairs that are close in horizontal plane. Maybe not seeing Rayleigh waves, will follow up on this.
    • Results in velocity estimates and eigenfunction profiles. Can compare to Pat's approach.
    • Vuk: Maybe we can combine these measurements with Pat's and do model selection for eigenfunctions.
      • Victor: there are many models out there, may have to constrain them a bit before launching into it.
    • Gary: active data may also constrain these, some of the models are definitely not supported by the data.
    • Daniel, Ross, Gary, Pat: will try to pull together all velocity measurements to start making comparisons. Pat will send the link again.

• Papers
  • Homestake Array Summary paper: pdf
    • Leads: Vuk, Gary, Victor
    • target: Seism. Research Lett., 6000 words, 10 figures.
    • Gary almost done with updates in the paper.
    • Vuk will send it for internal LIGO review when Gary is done. No objections to this plan.

• Active excitation overview paper
  • Leads: Gary, Ross
  • Others: Victor, Daniel,…
  • Will discuss at the next call.

• Surface Active Excitation
  • Leads: Victor, Boise
  • Others: Gary, Ross
  • Victor talked to Lee - they are planning a more general paper on H/V etc, will include the landstreamer data in it. Timeline: next couple of months to write it up. Happy to have input from us.
  • Vuk: it seems this would be decoupled from any papers we want to pursue.
  • Gary/Victor: Agree.
  • Vuk: let's invite them to give us a presentation in a couple of months, when they are ready.

• 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
  • Novel, but maybe insufficient for a publication. Could use the eigenfunction measurement for Rayleigh and assume something about Rayleigh field to make preliminary estimates of the Newtonian noise.

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

• Wiener filter application
  • Leads: Jan, Michael
  • Aim for late August.

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

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

• Very low frequency harmonics (Ross)