David's blog

Today is my last day working at Virginia Tech; tomorrow I fly back home. In the last three weeks since getting back from the field, I've been helping to get the GPS data in order, working on my abstract and poster, and then looking at the actual seismic data from the experiment and doing some preliminary analysis. The first two weeks were a bit slow, especially once the GPS stuff was mostly done and I was still waiting for the seismic data to be ready. Then when the data did come in last week, we had some trouble getting everything working in Promax and whatnot. I finally got started picking a few points and doing some simple 1D calculations last Friday and have been working on that this week. Although I looked a little at the refractions too, I've mostly been concentrating on the reflections while Michelle is doing models based on refraction. Many of our data sets have pretty clear Moho reflections, but I still found it could be rather difficult to pick the exact point of their arrival, since they are mixed in with the noise of the refracted first arrivals. Nonetheless, I made some picks and then plotted the squares of the time and distance in order to fit to the formula T^2 = x^2/v0^2 + 4*h0^2/v0^2, where h0 is the depth to the moho and v0 is the crustal velocity. Obviously, this is a pretty simple model, assuming constant crustal velocity and a flat moho, but it was intended to give only a preliminary model and was something I could do with only a week to work on it and no previous experience. By doing this for several shots, I was able to plot the results versus distance to get a rough idea of how things change along the line. The results of that are plotted below. I also tried today dividing data from each shot into multiple parts and solving for these separately, but this gave me a mess that didn't leave me very confident in the quality or consistency of my results, though perhaps I could do more to figure it out with more time.

I've finally learned to upload pictures on the blog. Thanks to whoever pointed out in the forums that you need to scale the pictures way down first. Anyway, here are a few pictures from both my trips to Canada this summer:

Our jeep getting pulled out of the mud on the surveying trip.

Odegaard Falls in the Bella Coola valley.

Me at the Bella Coola harbor.

Pounding in a stake during surveying. The snow on the ground here was gone in July.

A bear by the side of the road.

Fjord shores. This is the area I was deploying in in July and along which we had to find places to land.

Mountains and clouds, a fairly typical view during the boat deployments.

A little bay we landed in to place one of the instruments.

Geophone plastered to the rock.

Driftwood on the shore.

For the past about two weeks, I've been again in British Columbia working on the BATHOLITHS project. My main job in this was to help deploy and pick up seismometers, for which I worked along the coastal channels and fjords near Bella Coola, travelling by boat and placing seismometers along the shore. In some places we were able to bury the instruments, as was being done on the land-based parts of the line, but good soil was often not readily available since the shore consisted mostly of cliffs and steep rocks where all we could do was find an area not too steep to scramble up and a spot on the rocks flat enough to put the geophone and Texan, and so we would plaster the geophones directly to the bedrock. This took a bit longer than burying them, and getting the plaster the right consistency could be tricky, but generally it worked all right. The days were generally long, but the work was enjoyable and the scenery beautiful. Since we hadn't surveyed the boat parts of the line in June, we also had to do the GPS for them, which I and the others based in Bella Coola did on pickup, while the other two boats based farther west in the town of Shearwater did this on deployment. Pickup went faster than deployment, despite the extra GPSing and a slow start to the first day due to weather, and we almost finished in two days instead of the allotted three, but strong wind and waves forced us to stop the second day with only 12 stations left. The third day, however, was a beautiful clear day that I was quite happy to spend out on the water, and we were able to retrieve the remaining stations quickly. In between deployment and pickup the shots were set off, and I went with most of the rest of the team staying in Bella Coola to experience one. We were standing out of sight and I don't think there was much to see anyway, but we were able to feel the ground vibrate when it went off, which was pretty cool.

This past Thursday I got back from two weeks in the field in British Columbia and have been procrastinating on a blog entry since then. The purpose of the trip was to survey the seismic line in preparation for the the actual experiment in July, which mainly involved putting stakes in the ground and recording gps coordinates for the sites where the seismometers will be deployed. We used a high quality gps that Michelle had previously learned to use and taught the rest of us about, and as backup took some coordinates with a regular hand-held gps as well, especially when the bigger one was complaining that its signal wasn't good enough. We also had to scout out the roads a bit, seeing what was passable and what might be confusing and making notes for the deployers. Sometimes we learned the hard way, as when Andy and I got our jeep stuck in the mud and had to be pulled out by a local farmer. Nonetheless, I think the work went fairly well, and it was certainly an enjoyable trip with a good group of people. As we were leaving we learned that some of our stakes were destroyed by mowing of the side of the road and some were dug up when a ditch was dug along one of the forest service roads shortly after we had staked it, so they will need to be resurveyed in July, but most of our work should still be intact. The boat access part of the line will also need to be surveyed at that time as will a small hiking section, since we weren't doing those parts on this trip. There was also a small bit on the very western end that we were unable to get to because the road over a mountain pass was still covered with snow, which will hopefully be gone by July. Still, we did most of the land portion of the line, which stretches west from north of the town of Williams Lake to Bella Coola on the coast. The land between is very rural, and we saw wildlife including bears, moose, caribou, wolves, and eagles.