Homestake Meeting Minutes, 08/11/16

Attending:

Agenda: Andrew, Gary, Jan, Michael, Victor, Voon, Zhi, Vuk, Pat

• Tanner graduated - Congratulations!!!
  • Gary/Vuk: post his disertation on the wiki.
• Homestake Status
  • Daniel (email): I am on DQ shift this week, and while the data seems to be OK (with the known exceptions, RRDG, etc), it seems Tanner's DQ page is missing most of the links. Maybe a directory was moved around or permissions changed? In any case, the Caltech DQ page is still OK (same links and everything else).
  • Pat: transitioning from Tanner, will have to update the links.

• September trip to Homestake,
  • Sept 23-28
  • Gary, Daniel, Vuk (partly), Voon
    • Gary: giving a talk on Sep 20th and was planning on driving, so can't make it to Homestake before 09/23. Will have a pick up truck, so we need small car rental.
    • Victor: safety training for Voon?
    • Vuk: will check, but for surface work we should probably be OK.
    • Would be good for people flying in on 23rd
    • Daniel (email): still on board for the trip in September – just waiting to hear finalized dates before booking anything.
  • Tom should be OK throughout
  • Preparatory work: RR, contact private owners
    • Gary: the week before, will call the private owners to schedule the times preferable during the weekend. Also will have to call the school - maybe do it during the week, do some outreach. Gary will contact the teacher.
    • Vuk will have to develop the workplan and will have to schedule RR maybe for Monday.
    • Gary: will have to go to the roof to take down the radio, sometime during the week. Last time Jamey used the one-person crane to install it. Schedule it for monday so that we have time to react on problems.

• Data analysis
  • Levi (email): Tanner, Pat, and I met on Wednesday of last week to go over Tanner's parameter estimation routine. He mentioned that it was available on the SVN, but I haven't been able to access it. Either I am having troubles with SVN update, which would be unsurprising) or I need to checkout something which I don't have the name for. Anyway, I will talk to Pat about this to see if he is having any issues.
  • Michael/Jan pdf
    • Michael: initially did the analysis with 4 stations and got 50x suppression at 0.2 Hz, with some residual structure left over. Now trying to repeat it with the larger array: more channels and larger area. For coherence, using all stations including surface and far-away ones.
    • Improved to 100x subtraction at 0.2 Hz, no left-over structure in the residual. Using only sub-surface stations for the filter, adding the surface stations did not make much difference. Some excess noise was included at low frequencies - not sure why, in principle the filter should not get worse if you include more data (but in practice, numerical issues could cause a difference).
    • Michael: will also try to make the filter based on the surface stations only, for comparison.
    • At 1 Hz still have 5-10x subtraction, and higher frequencies less suppression (2-3x), affected by local disturbances. Might be able to improve at high frequencies. Have 1.3 Hz and its harmonics which are not plane waves.
    • Jan: looked at the k-f maps, produced using the phases between stations and fitting a 3D plane wave to them, averaged over some time. Trying to understand if there is body-wave component in the microseism, which might explain why the initial Homestake data subtraction was not fully successful.
    • Victor: a number of papers now confirm that body waves contribute to the microseism, typically small contribution and pointed to the storm.
    • Jan: now we fully subtract the microseismic peak, so wanted to look at the k-f maps. But turns out to be hard, the maps seem useless. The wavelength at 0.2 Hz is very large compared to the array size. Possibly the reason may be that there are likely two main contributors, one from Greenland and one from the Pacific/Alaska, which cannot be resolved with a simple k-f map.
    • Vuk: should try to look at the radiometer algorithm, may be able to separate two sources.
    • Jan: For the Wiener filter paper this is it. We would like to determine if there is a sign of body waves in the microseism, would demonstrate that the body waves could be overcome by a 3D array, which would be a good result.
    • Victor: could try to look at different times of the year, they should give different data and different source.
    • Jan: maybe try to use spherical wave models to deal with the local sources at 1.3 Hz. Not soon, but would like to do.

• Zhi Li 113442_deep.pdf, 113442_surface.pdf, 113522_deep.pdf, 113522_surface.pdf
  • Study of an EQ in Japan, looking at the structure of scattering. Looking at the direction of the incoming wave at different depths. Doing the fk analysis at a specific frequency at the first arrival (P-waves) and then 40 seconds later (well before the surface waves arrive). Using the vertical component of the wave, plotting the horizontal directionality (slowness). Divided the stations into deep (4850+4100) and shallow ones (surface + 300). Using 20sec of data for Fourier transform. Direction near vertical, ellipses peak near the origin.
  • Zhi: Strong difference between deep and surface stations suggests that the shallow structure modifies the wave.
  • Victor: think that the deep plots are stretched by the geometry of the stations.
  • Jan: there is a strong local peak at 1.3 Hz. Why this frequency?
  • Zhi: searching 1.2-1.4 Hz band and choosing the highest signal within this band.
  • Victor: during the EQ, the signals is orders of magnitude above the noise.
  • Zhi: for future, will look at how much station geometry matters, look at the incident angle