The critical zone (CZ) represents the outermost layer of the Earth where interactions between the atmosphere, soil, bedrock, and organisms regulate the formation of life sustaining resources. For many decades investigating the deep CZ (> 5 m) where the important regolith/bedrock boundary sits and where water reservoirs reside was largely inaccessible owing to the time and cost of drilling/hand augering. Recent advances in standard geophysics methods and instrumentation now allow us to probe the CZ at previously inaccessible scales and depths. Despite extensive research into the CZ, fundamental questions remain regarding how the CZ forms, how the CZ evolves, and how the CZ will change in the future. This project will consist of 4200 geophones and 62 3 component nodes over a 300 x 300 m2 area. I will be tasked with processing and analyzing the dataset. Initially, I will pick first arrivals on refraction lines and develop a velocity model. Eventually all of this will lead to interpretability and understanding the subsurface structure.
The reason I waited and lumped these three weeks together is that I was told the coming weeks would be much of the same work.
Up until the third week, Kat and I had been working on the same data. Now I have my own set of data to work on. I continue to do much of the same things that I was before, but this time on my own seismic lines. Essentially picking first arrivals. Also, since I have past experience in well log analysis, I will be implementing that into my data as well. All of this will result in a comprehensive understanding of this specific CZO to the depths of around 50 meters. So, the data is not deep and one may assume it to be uncomplicated, however, it is foreign to me since I have only dealt with deep seismic reflection data. The techniques for refraction and reflection would not seem to be so different. Well, they are and it takes a completely different approach to processing and interpreting. The challenge is welcomed!
As for the assignment this week, in regard to the elevator speech, it was not too difficult. The biggest difficulty was to have a distinct difference in the speeches of Kat and mine. Our projects are quite similar. Overall it was easy because I guess thinking about our difference in our projects helped in developing a better understanding of the project as a whole. One must also consider the type of audience in developing this speech. Most likely there would be multiple elevator speeches based on people's backgrounds. In an interview, you could most likely be more technical. In everyday conversation with people that lack an earth science background, the speech would be simplified. Many of the technical jargon must be removed, not only for them to understand you, but to not come off as pretentious.
I began running reciprocity checks on my own first arrival picks. At first it was terrifying because they were all over the place! As time when on, they became more refined but still nowhere near where I’d like. However, this is science and the world is not uniform. The data looks ok but not ideal. It has nearly reached a point of acceptance that it will not be perfect.
It also creates an offset at certain areas because the seismic line I am using is an arbitrary line across the grid. This generates a slight offset with arrival times because they are not evenly spaced. Generating decent reciprocity checks was the most challenging and most satisfying. Some would look horrible but some would look like the one pictured above. It is a love hate relationship since reciprocity checks tend be a good guide for data consistency.
Below is a map of the study area generated in Matlab. Each tiny red dot was a receiver. So, clearly there was a ton of equipment in the field that we had to deploy.
This week I have been running Seisimager and developing tomography maps simultaneously with correcting my picks. It becomes pretty reiterative but who said science was always fun!? Below are all of my picks on a single line and the resulting tomography. It was pretty tricky matching the low velocity zones at the beginning of the model. Most of that is loosely packed sediment so it moves at nearly the speed of a fast car. The fluctuation in velocities is unheard of to me. One model had a fairly well matched low velocity at 80 m/s and a max velocity of around 5000 m/s.
As for a paper that is most useful. I have adopted a textbook instead of a paper. It is called Applied Seismology and I claim it to be the Bible of shallow seismology. It had everything from first arrival picks, filtering noise to interpretation. I am ‘borrowing’ it from the lab and have it in my apartment at my work desk.
Hello all again,
This past week was a learning process to say the least. To start off, I now realize I have a significantly worse understanding of Matlab than I initially assumed. Though, we may not be writing all too much code, it still is enough to get me stumped. Luckily, Kat, the other intern, and Natalie, our advisor, are wonderfully knowledgeable on the interworkings of Matlab. Also, Seismic Unix is often used in conjuction with Matlab to pick first arrivals, and that is not terribly difficult.
It is quite neat dealing with data on such a large scale and potentially the largest study of its kind, and being some of the first to observe it. It is both daunting and exciting. That is because our advisors sometimes do not know the next step in the process, as it is also a learning experience for them. This actually helps all of us gain a better understanding of the dataset on a fundamental level because if we don't gain a better understanding, then there can be no progress made.
Currently, my main goal is to be competent if not proficient in all the many softwares we are dealing with. I am currently reading multiple manuals because it seems we impliment a new software or plugin each day. It will pay off to stay on top of learning these skills since it will make my work that much more efficient. All in all, I can't wait until we start developing seismic inversion maps in the coming weeks using seisimager.
Here is a screenshot of 1 of the 4200 shots we obtained the past week (including first arrival picks)
I’m Joey, one of the IRIS interns from the University of South Carolina. To start off, I am incredibly thankful for this opportunity and look forward to what these next few months have in store.
The program began with an orientation that was very enlightening and fun! It had a good mix of opportunities, whether it was learning, exploring or unwinding. Even though we had 12+ hours of ‘work’ every day, it was well worth it. Plus, being surrounded by extremely happy, friendly, and intelligent people made it ten times better.
As for my first week at Penn State, it was eventful to say the least. Putting out 2100 geophones is no easy task, especially when the study area from end to end is 600 meters long. Luckily, we had around 25 volunteers but those numbers quickly dipped as the week went on. The area was muddy and carrying 8 Texans at a time, in your backpack, is not light. On top of that, we had to worry about ticks because Lyme Disease is fairly popular in the Shale Hills Critical Zone. Overall, trudging through the mud, swatting mosquitos and carrying forty pound boxes was well worth it! The data we obtained is incredible and I can’t wait to process and interpret it!