It is hard to believe that next week is officially my last full week of working in the lab. After that, I will be in the field for the last 2-3 weeks of the internship, which I’m really looking forward to. While it has been a productive week, the realization that the end is near has also made it somewhat stressful. Although I’ve accomplished more than I could have hoped during the past month and half (especially becoming comfortable with the computer programs), I don’t feel that I have any obvious “results” as of yet. And I definitely have a long way to go before I’ll have an abstract that I’m happy with submitting to AGU, not to mention a poster. With that being said, I’ll still have a few weeks in the field to start looking over what I have done so far to begin connecting the dots. Chances are, I’ll also have most of week 10 to work on my abstract and poster, but my goal is to get a rough outline for my abstract done next week.
This week, I’ve been continuing my work with the move-out plots, trying to come up with decent velocity models for the basin region. It is a very tedious process of changing numbers in a text file, seeing how they look on a move out plot, comparing this to the real data, making corrections (this is the hard part), and repeating the process until the synthetic model looks close to the data. So far, I made a rough model for the Illinois basin below station R44A that matches fairly well for the shallow structures:
The real data is on the left, and my synthetic model is on the right. On the x-axis is ray parameter which tells us about the incidence angle of the incoming P-wave and on the y-axis is the time after the direct P-wave arrival. The red represents positively polarized arrivals while the blue are negative arrivals. What you are looking at are arrivals of direct P to S wave conversions and their reverberations in the crust which tell us about the structures, referred to as “converters”, in the crust. We are mainly interested in looking at the fine, shallow structure of the basin (closer to the bottom on the picture) and seeing how these structures can impact the Moho signal that we are seeing.
I have found that there are many ways to model some of the structures in the crust, so Hersh has been helping me sort out which possibilities are more likely in reality. The model shown above has 5 layers, 3 of which are less than a meter in thickness which would usually be considered too thin to include when modeling receiver functions. It turns out, these thin shallow layers sort of “trap” the wave energy as it reverberates causing some very complicated signals that appear later in time and therefore appear to be deeper in the crust. Now that I have this basic model for the basin, I will try to model the crust outside of the basin area in Missouri to compare the differences. Hopefully, in the next week I will be able to make some connections between the crustal structures of the basin compared to the regions outside of the basin.
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