Homestake Meeting Minutes, 07/14/16

Attending: Gary, Ross, Levi, Vuk, Daniel, Pat, Tanner

Agenda:

• Homestake array status
  • RR cabling issue: probably rodent activity. Fix would most likely require replacing cables.
  • WTP mass rail issue.
    • Gary suspects that the platform has tilted in one direction, so that the instrument is not leveled any longer. We would probably need to have a spare sensor ready just in case though.
  • Do we need a maintenance trip asap?
    • Gary: Cost roughly $20 per station per day, so next 50 days would cost us $2000, which is about the same as the cost of a trip to fix these.
    • Gary/Vuk: On the other hand, do we gain much from the extra 2 months of data from these 2 stations. Gary and Vuk feel that we do not, given how much data we already have. Others agree.
    • Decide not to worry about these two stations, our next trip to Homestake will be to decommission the surface stations in September.

• Planning the September trip to remove surface stations:
  • Vuk: have to leave each site in the state we found it. We have to extract the insulation from the vaults, and we have to remove the pole.
  • Gary: The pole might be hard in some cases, in most cases just pulling one guy wire could do it (since they are shallow, may have to dig a bit). A couple of sites may be harder since they are deeper - for them, may have to dig more and maybe hit the concrete.
  • Gary: could decommission up to 5 stations per day. But have to service the balers in parallel with this. And we have to check the orientation of the sensors, to get another data point.
  • Also have to clean all of the equipment (remove mud etc), pack them into their boxes. We should ship them in December, along with all the underground equipment.
  • We should allow a full week for at least 3 people: arrive on Sunday and leave on Friday or Saturday.
  • Dates in September: Gary would prefer the second half of Sept. Pat OK. Daniel: weeks of Sep 19 and 26 are ok. Ross: will be taking classes, but could miss some. Vuk: teaching, but will try to join for at least a part of this trip.
  • Pat: What about the tools at Homestake? let's take inventory in Sept, and decide what to leave in the lab and what to ship back to UMN in Dec.
  • Week of Sep 26 looks like the best choice. Follow up via email, Vuk will check with the lab.
  • Email from Jaret (after the meeting):
    • Maintenance days: Sep 23,26 and Oct 7,10. The Lab also observes the Native American Day holiday on Oct 10.
    • Tom's availability: Sep 24-26 (weekend), traveling say Fri Sep 23 (there is another group earlier that week and Tom needs to manage his hours). Also, week of Oct 3 looks good.

• Data analysis updates
  • Preliminary Love Wave Recoveries: pdf
    • Vuk: next step would be to implement the actual Homestake array. Will have to worry about topography?
    • Gary/Daniel: at low frequencies the wavelengths are very long, so the topography effects would be small. At frequencies ~1 Hz and above, the wavelength is similar to the topographical features, so the waves may bend and follow the topography. Theoretically not clear how to deal with this, and it would depend on the actual geology at Homestake (whether the inner layers also bend, or only the surface).
    • Vuk: how do we verify this algorithm with data? Maybe compare to other techniques?
    • Gary: could look for noise from a nearby mine, there is a lot of activity there. But this is at higher frequencies, 1-10 Hz.
  • Gary: working on the active source data from the surface weight drops. Now at the stage of measuring arrival times at different stations from individual shots. Had to rearrange the data to make sure the shots are matched at different stations, have to do it interactively. Hoping to get something together for an AGU abstract, Aug 1. Estimating ~30,000-40,000 measurements so have to do it efficiently.
  • Ross: trying to study the elliptical particle motion, debugging an older piece of code to do it. More next time.
  • Daniel: have visiting summer student who spent 2 weeks at Boise working on the inversion problem for the near-surface structure. Should be able to show it next time. Trying to decide now how to push this further.
  • Daniel: Boise state group has tools to estimate directions from active source data, which may help Ross/Gary in their efforts. Gabe is the graduate student to talk to.
  • Try to think more about what what papers we should publish. Plan to have a discussion at the next meeting. Vuk will email about this.