Arianne's blog

Sum it up

Submitted by Arianne on Tue, 2007-08-14 21:24.

Here I am sitting at my computer on my last day of the internship. I figured I should reflect a little while I have the time and everything is still fresh in my mind. To do this I looked back at my first real post.

1) My post is a huge chunk of text which made me realize how much I love paragraphs.

2) I have a nice summary of what I was planning on doing this summer, and that's actually what I did.

3) Goal 1 - look up RTD bus route. Check, that was really successful.

4) Goal 2 - Be a sponge. This was a good goal. I learned a ton this summer about seismology, receiver functions, writing scripts, SAC, GMT, and MATLAB. In addition to learning things about my project I also learned lots about the Rio Grande Rift and the current GPS study involving that area from the other intern. It's hard to realize that I have learned so much because I learned everything gradually. It wasn't a big defining moment where magically I knew it all, I worked to know it. Since I am going to continue working for my host during the school year all of this knowledge will be useful and that will be the true test of how well I know everything.

5) Goal 3 - Become more active in the geophysics world. I joined AGU and SEG. I am not recieving their publications (like EOS) and love reading them. It's nice to know what else is going on in the geophysics world.

6) Bring a jacket to work. Double check. I still froze and even had to take a walk outside during lunch to get warm, but the jacket was helpful.

7) Be prepared for AGU. I think I will be well prepared for AGU with the help of the people I have been working with this summer. Now the big decision is trying to figure out which figures and plots to put on my poster. My abstract is still in the editing phase but it's coming along.

Overall I am very satisfied at the conclusion of my internship. I don't think things could have gone better (minus the freezing). I would like to thank everyone involved for making this a pleasant experience.

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Abstract Thinking

Submitted by Arianne on Tue, 2007-08-07 18:34.
Here are two drafts of my abstract for AGU.  I'm still not happy with either so they will be changing over the next couple of weeks.  Any suggestions will be greatly appreciated.

Draft One:

In the year 1987 Congress designated Yucca Mountain in southern Nevada as a disposal site for radioactive waste.  For this reason there is much interest in the surrounding area.  A basin and range geology dominates this area with lots of Miocene ash flow tuffs.  Looking at the area using seismology can help display more information as to what is beneath the surface.  There are many seismometers in the Yucca Mountain region some of which are located in the Nevada Test Site.  Some of these seismometers record broadband while others record short period.  Each channel from the station collects data at 20 samples per second.  The data was collected using passive source seismology.  The focus was from earthquakes between 30 and 90 degrees away from the area during the years 2000-2005.  Each event has a magnitude greater than or equal to 5.8, with the largest earthquake being of magnitude 8.3.  To process this data UNIX-based Antelope was used.  The data was stored in a database containing event information and station information.  Using these databases receiver functions were calculated using the iterative deconvolution method from Ligorria and Ammon.  During this process the data was rotated, filtered, and cut in Seismic Analysis Code (SAC) to be of more use.  After the receiver functions were calculated stacked and moveout plots were made.  This processing was done in MATLAB with a script by Vera Schulte-Pelkum.  These plots were often difficult to interpret because of the local geography.  When the seismic waves travel through a basin the sediments create many reverberations.  Unfortunately these reverberations show up in the moveout plot and at times drown out the other signals.  From these moveout plots the moho is visible along with a midcrustal boundary. 

Draft Two (Most recent):

The area surrounding Yucca Mountain is predominantly basin and range terrain with many Miocene ash flow tuffs.   Looking at the area using seismology can attempt to explain some of the anomalies in the area.  A large gravity anomaly is located just north of Yucca Mountain with a huge contrast between high and low gravity.  The gravity anomaly could be caused by a difference in crustal thickness.  When the crust is thick there is less mantle, which is dense, below the area creating a low gravity zone.  There are about thirty 3-component seismometers in the Yucca Mountain region, some of which are located in the Nevada Test Site.  Each channel from the station collects data continuously at 20 samples per second.  The short period data collected from passive sources seismology is able to show the crustal thickness in the area.  The data is from earthquakes between a 30 and 90 degrees distance from the area during the years 2000-2005 covering a wide back azimuthal range.  Each event has a magnitude greater than or equal to 5.8, with the largest earthquake being of magnitude 8.3.  From the seismograms receiver functions were calculated using the iterative deconvolution method (Ligorrîa and Ammon, 1999).  After the receiver functions were calculated they were stacked and moveout plots were made.  These plots were often difficult to interpret because of the local geology.  A sediment layer is seen in most of the basins, which causes more complexity in the velocity model for the area.  This sediment layer also produces multiple reverberations, interfering with the useful signal.   From the moveout plots the Moho is visible along with a midcrustal boundary.  The Moho is usually seen near 4 seconds and the midcrustal boundary around 2 seconds.  At certain stations the Moho is only visible from specific back azimuths, possibly due to a dipping Moho.  Through out the area the crustal thickness is fairly constant, not helping explain the gravity anomaly.
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The Beginning of the End

Submitted by Arianne on Fri, 2007-08-03 15:29.

I am excited that we can load pictures!!! Since my last blog a few things have happened. Yesterday I did my "final" presentation to the group. There were about 7 people who attended and overall it could have gone worse. It was a nice short little power point with nice pictures. The best part was showing my results and having other people look at them. New eyes always see something different. Today is technically my last day as an IRIS intern, but I am going to keep working over the next two weeks. Then once school starts I will continue working with my host on a new project. Hopefully over the next two weeks I will finish up my project, do my abstract, and do my poster. For now I want to share my images with all of you...

Station TYM (the one shown) is north-west of Yucca Mountain. This is the plot I was talking about last time (with some nice changes thanks to Andy). In the upper left corner is the moveout plot sorted by slowness. We are able to see a strong arrival around 3 seconds. The two plots on the right show stacked receiver functions. The receiver functions are sorted by backazimuth (the angle of which the earthquake is relative to the station, north is 0). The sorting is important in case the signal is different coming from different directions. On interesting thing noticed at this station is the strong positive (red) arrival at 3 seconds in the radial that flips polarity in the transverse. Looks like something interesting is happening there, just not sure what yet.

Station BTW is only slightly north of Yucca Mountian. This image is of multiple moveout plots of events from only specific backazimuths. The plots are 0-90, 90-180, 180-270, and 270-360. This is of interest because the Moho is shown nicely just after 4 seconds on the moveout plots from the SE and NW but does not show up from the other direction.

AMD is station farthest south of Yucca Mountian that we have data from. This plot is again a moveout plot but with moveout curves on the image. These moveout curves are based on a velocity model (which may be changing) from the area around Yucca Mountian and the Nevada Test Site. Here the plot shows moveout curves for interfaces at two depths and their reverberations. We are considering adding a sediment layer to our velocity model because the area is basin and range.

That's all for now. I am slowly working on my abstract and will post that when it becomes presentable.

This work is not funded by the Yucca Mountain Project and the results are not necessarily endorsed by it.

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Actual Results

Submitted by Arianne on Wed, 2007-07-25 17:09.

It's exciting to get results. No matter how bad or wrong they look. I have finished making receiver functions for around 30 stations near Yucca Mountain. With these receiver functions I have made moveout plots. I was really excited to show everyone the plots, but I can't upload images. Cry I guess I can still talk about them and then post a picture when the whole upload thing gets figured out.

In thefigure there are four plots. The plots are of moveout from the radial reciver functions, a histogram of the number of receiver functions at each backazimuth, and a stack of the receiver functions sorted into backazimuth bins. The one problem is that the stacked data doesn't seem to show the same arrivals and crustal features as the moveout plots. My new goal is to figure out how to make those look alike. If anyone has ideas or suggestions that would be greatly appreciated.

Other than the figures I'm making I am beginning to work on my abstract for AGU (which I might not get to go to, but that's a different story). Next week on Thursday I will be presenting my research to the other interns, my advisor, the other people helping me, and whoever else happens to be around and wants to listen. That should be good practice. Let's hope I have everything figured out by then and actually have nice data to present.

I'm off back to solving the big problems of the day. I'll post again when I can post images.

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