Stage 2

The second stage of the project was a bit harder to get started with. The task itself was fairly straightforward: to pick the arrival point of the p-waves I had selected during the first stage of sorting. However, I needed to continue to build on my understanding of the terminal in order to get the files ready to run with the new picking program.

The first day, Professor Ford met with me and directed me through the process. First, I combined all of the selected files from the first stage saved in the Mark1 files into one file if any had multiple Mark files. I then created three copies of this file and named each 'Mark1r.txt,' 'Mark1t.txt,' and 'Mark1z.txt.' I then opened each in xcode and used the find and replace function to replace all of the '.z.'s in the file names with r or t for the r and t files. I then used the terminal to move all of the selected files from SAC to a new bpband folder. From there, I was ready to make the macro for the new program. Using the terminal window, I generated a new macro list, and then used the terminal to open the program to begin picking arrival points. For each waveform, I would zoom in on a broad area around where I thought the signal arrived, then press T and 1 with the cursor hovering over the arrival point to mark it. Then I would press Q to move on to the next wavelength and repeat until all arrival points had been picked.

Initially, everything seemed to make sense with Professor Ford's guidance, though there were many steps to keep track of. I took what I thought were detailed notes along the way, but as I began to repeat the process myself, I started to find holes in my notes. Because my notes were handwritten, there were places where the terminal code was not correct simply because I hadn't thought to be careful enough in denoting where a space should be, or what a symbol was. For example, I couldn't get my waveform files to move because I was typing “chmod utx move_ranked.csh.” When I asked Professor Ford for help, she said that the 't' in 'utx' was supposed to be a '+,' so I went back to my notes and sure enough it was shorter than I usually write my t's, but I decided to add 'plus' over the symbol to better remind myself in the future. It took me two or three days of getting used to the process, asking Professor Ford for corrections here and there, and modifying my notes to finally get the process to run smoothly. Once it did, though, it was very smooth sailing and I was able to gain a much better understanding of the terminal process and complete picking p-waves relatively quickly.

Picking the p-wave arrival times themselves was fairly straightforward. Most of the files had clearly visible arrival times, so I was able to pick them in just a few seconds and move on. A few, though, were not quite as clear. After a while, though, I found a good rhythm by zooming in on a broader section so I could get a good sense of the pattern before and after the arrival time. In doing so, I could spot exactly when the patterns shifted from one to the next, and picked the arrival time accordingly. This whole process only lasted a couple weeks as opposed to the initial stage, so we were quick to move on to the third stage once all of the seismic station files were completed.

I started the GEODE internship with Professor Ford around mid August. I have only a handful of introductory and field geology courses from RCC this early in my education, so Professor Ford was kind enough to spend our first few meetings giving me a crash course on seismic waves and anisotropy. My understanding thus far is that I am looking at seismic waveforms and how the waves bounce around as they pass through different materials in the Earth's interior based upon when and how strongly they arrive at each of the different seismic stations I am processing data from. I will eventually be able to use that data to construct a map of the Moho area between the crust and the mantle. I have been learning the processes one step at a time, and doing as much reading as I can on the side, so I have a little bit of a shaky understanding of the big picture at this point, but it becomes clearer with each new step so I am looking forward to seeing everything come together with the final results.

The first step in getting to work was learning to run PQL. Professor Ford explained that she had already cropped the waveforms to show only p-wave arrivals. My job was to then use PQL to sort through each of the waveforms to select those with a clear arrival, and discard those without clear arrivals. I was warned that PQL could be a difficult program to work with, and that I would soon be dreaming about waveforms because I would be spending the next few weeks sorting through about ten seismic stations in northeastern California and northwestern Nevada with about three or four years worth of data each, plus one folder with more than ten years of data. The most difficult thing for me initially ended up being simply adjusting to using a Mac. I've been a PC person my entire life and have only ever watched people use Macs briefly during presentations, so I was glad to finally have an opportunity to sit down and see what the big deal was. It took me a few minutes of exploring to realize that there really was no big deal—most everything was really very similar to a PC, just labeled slightly differently, sort of like looking at a PC in a funhouse mirror. Once I explored a bit and realized all of the hot keys were the same, it was smooth sailing...apart from the fact that I will never understand why the save bar is affixed to the desktop instead of the program window, but c'est comme ca.

Anyhow, Professor Ford showed me how to use the terminal to run PQL. The most difficult part of this step was simply learning the terminal commands. For this phase of the internship, all I really needed to know was cd to change directory, cd ../ to move up one folder, and ls to list the files within the selected directory. After only a few uses, these became engraved in my muscle memory. To begin the process, Professor Ford selected the seismic station O05C in north eastern California to demonstrate. I then opened the folder titled 'bpband' to display the list of waveform files and left that off to the right side of the screen. On the left, I used the terminal window to change the directory to the O05C file by typing “cd Documents/Project/NorthernBasinRange/O05C/bpband,” then once I hit enter to change the directory, I simply typed “PQL” into the terminal window and pressed enter to run. Once PQL was open, I clicked on the 'Traces' button to the left of the PQL window and selected five waveforms. I then selected 'Mark' also to the left of PQL and clicked to highlight each of the waveforms with a satisfactory arrival signal, and pressed enter to save in a file titled 'Mark1.' Once saved, I would manually move the files I had loaded on PQL from the bpband folder to the folder titled bpdone. Then I would load the next five waveforms, and repeat the process over and over until I had sorted all of the data.