This summer, I will invert seismic data to construct a phase velocity map of Africa. When any "source" causes the ground to move (think: earthquakes), energy is released. This energy then travels through the ground as seismic waves, which can be recorded by a "receiver" (think: seismometer) at another location. If we know where the source and receiver are, then we know how far the seismic wave traveled. Furthermore, if we know when the source released energy and when the wave reached the receiver, we know how much time the wave took to travel. With this distance and travel time, we can estimate how fast the wave traveled. To seismologists, these velocities are especially interesting, as they depend on the material through which seismic waves travel. As such, knowing the velocities through Earth can clue us into what composes our planet! On a smaller scale, seismologists use inversion find the seismic velocities through a particular region. We first collect many records of seismic waves, all of which travel throughout that region. Next, we create a series of models, each assigning different velocities to different parts of that region, and see how well those models are consistent with our data. Our goal is to find the models that are most consistent. Using inversion, I will construct those maps for Africa, showing how fast seismic waves travel across the continent. Specifically, I will use a method with relatively new applications to seismology, Bayesian inversion. I will then analyze my resulting maps by comparing them to one another and to those of previous studies, so stay tuned! (P.S. For more on seismology, see Introduction to Seismology by Peter M. Shearer, and for inversion, see Bodin and Sambridge, 2009; and Olugboji et al., 2017)
Wow, I cannot believe it is already the final few weeks of my internship! Reiterating one of my previous posts, time certainly flies. Now that I am almost at the finish line, I would like to reflect on my experiences thus far, especially as to how they relate to my future.
Overall, I loved my experience as an IRIS intern. In particular, I enjoyed being able to fully invest in my research. My daily activities --- including diving into the literature, writing and testing computer programs, and drafting my manuscript and AGU poster --- taught me something new about my project, as well as the research process itself. From the background and motivation of my research, to the mathematics and programming governing my central methodology, to effective presentation skills, I learned so much! These learning experiences have been further enriched by the structure of my internship. Unlike during the academic year, when my attention is split between coursework and research, during the summer, I have the opportunity to devote my time and attention to research.
Before becoming an IRIS intern, I was interested in a career in seismology research. My experiences as an IRIS intern strengthened these aspirations. I enjoyed immersing myself in research, and my learning experiences fueled my scientific curiosity. By all means, I want to continue pursuing such experiences. During the upcoming academic year, I look forward to finishing my IRIS project and pursuing a Senior Thesis, a year-long research project, in seismology with Princeton faculty. Following graduation, I intend to pursue a PhD in seismology. I am grateful to have developed the experience and research skills valuable to my future plans. I am certainly excited to continue my learning and training as a seismologist!
I have so many people to thank for my fantastic summer! Thank you so much to:
Professor Olugboji, for being an attentive and encouraging mentor and for taking the time to teach me so much;
The URSeismo group, for your collaboration, support, and enriching group meeting discussions;
Mr. Michael Hubenthal and the IRIS team, for this valuable learning experience;
My fellow IRIS interns, for a fun and supportive learning environment;
And my readers, for following my summer research.
I will do my best as I complete this research and pursue future opportunities in seismology.
Stay tuned! And to my readers attending AGU (in-person or virtually), see you soon!
This week, I have been asked to reflect on the challenges I encountered this summer. As you may know, my research is entirely computational. Other than writing my abstract for AGU and my manuscript, my work consists of composing code. So far, my biggest challenge has been finding and fixing mistakes, or "bugs," in my code, as I discussed a few weeks ago. This week, I would like to elaborate more on that.
Sometimes, "debugging" my code is relatively simple. After execution, programs may return an error message, identifying where a mistake is located. In these cases, debugging only requires scrolling to that location and fixing that error. Other times, however, the program might not show me where a bug is located. This is especially the case when a program runs smoothly, but the result is not what I expected. I must then search through my program to find the mistake, and the process may be frustrating, especially for larger programs.
Several skills I developed have been instrumental in debugging.
Careful attention to detail: Sometimes, the source of a bug is small, such that it can be difficult to locate at first glance. That bug may be a typo, causing one variable to be called instead of another. Alternatively, I may have forgotten to add a piece of code. In programs spanning hundreds of lines, finding these errors requires me to search through my code carefully.
Organization: In such large programs, identifying what each piece of code does may also be challenging. Of course, I understand their function in writing my code. However, that may not be the case when I revisit them later for debugging, adding additional difficulty to the process. Ensuring that my programs are organized prevents such confusion from happening. By neatly formatting my codes and providing comments to explain their function, I allow myself to better understand my programs when revisiting them, resulting in a smoother debugging process.
Best practices: In addition to the aforementioned skills, I learned several "best practices" for debugging. For example, to see the variables and values used by my programs, I can instruct my programs to print intermediate values to the terminal. By identifying potential errors as the code runs, I can better pinpoint their sources. Another practice, if the coding language allows, is to insert "debug points" into my program. Debug points pause the program during execution, allowing me to check variables and functions and search for errors. As with using print statements, using debug points allows me to narrow down the locations of bugs.
I am glad to have developed these skills, especially because I want to further pursue the computational side of seismology. I look forward to furthering these skills in the final third of my internship, as well as during future research experiences.
Thank you for reading, and stay tuned for more updates!
This week, I have been asked to share another figure pertaining to my research, as well as the most important paper to my work.
I have been preparing to construct my phase velocity maps across Africa! These past few weeks, I have been writing codes to run the inversion algorithms, once I receive the data I need to construct my maps. Not only will I construct phase velocity maps using my data, but I will also construct phase velocity maps using existing models. Several models have reconstructed how fast seismic waves travel throughout Africa. Some of these models focus on surface waves, like in my project, or body waves, from which I can calculate the corresponding phase velocities. I plan to construct phase velocity maps from those models and compare them with my own. In doing so, I can place my results in the context of the wider geophysical literature. Furthermore, I can identify how my maps advance our understanding of the African crust.
In the figure below, I show one phase velocity map from another model, specifically, one of the global surface wave models constructed by Ekström, Tromp, and Larson (1997). This model reconstructs the phase velocities of surface waves across the globe. The figure below zooms in on Africa, and shows how the phase velocities of Rayleigh waves (one type of surface wave), at a period of 35 seconds, change with respect to a "reference" velocity. Currently, I am converting these velocity changes, in percent, to velocity values in km/s, so that I can compare this map to my results. Stay tuned!
2. Most Important Paper
As you may know, my project will reconstruct the phase velocities across Africa from seismic data. Though many methods exist for doing so (see Nolet 1987), I will use a form of Bayesian inversion. One of the first papers to discuss and apply this method to tomography is Bodin & Sambridge (2009). This paper highlights Bayesian inversion as an innovative method for tomography that resolves the limitations present in other methods. For example, many common inversion methods only result in one final velocity model. In other words, they result in one solution as to how fast the seismic waves travel throughout a region. While that meets the objective of tomography, we do not know how accurately our model reconstructs seismic velocities. In other words, we do not know how much we can trust our model. By contrast, Bayesian inversion generates many final models, the standard deviation of which can be used to obtain a sense of uncertainty. The higher the uncertainty, the less confident we can be of our results. This resolution, along with several others, makes Bayesian inversion more efficient and promising than other inversion methods. By all means, it is a suitable choice for my project!
Bodin, T. & Sambridge, M. (2009) Seismic tomography with the reversible jump algorithm. Geophysical Journal International, 178, 1411–1436. doi:10.1111/j.1365-246X.2009.04226.x
Ekström, G., Tromp, J. & Larson, E.W.F. (1997) Measurements and global models of surface wave propagation. Journal of Geophysical Research: Solid Earth, 102, 8137–8157. doi:10.1029/96JB03729
Nolet, G. (Ed.). (1987) Seismic Tomography With Applications in Global Seismology and Exploration Geophysics. Seismology and Exploration Geophysics, Springer. doi:10.1007/978-94-009-3899-1
This week, we have been asked to share:
Without further ado, here goes:
1. One challenge
An ongoing challenge in my internship is writing and wrangling with computer programming. Writing code requires me to be conscientious about many things. For one, I must ensure my code runs without error. If I run into an error, or a "bug," I brainstorm possible solutions and consult my mentor and online sources for help, thus "debugging" my code. Of course, even if my code runs smoothly, I may run into subsequent issues. For example, my code might output something wrong or unexpected. Right now, one of my programs is outputting complex numbers when it really shouldn't! As I learned from my mentor, situations like these show the importance of thoroughly checking my code's results. After all, unnoticed mistakes can cause serious errors down the line. As such, fixing mistakes is better done sooner rather than later. Another potential issue is the amount of time my code needs to run. Even if my program works correctly, its method might not be the most efficient. A method that should take hours to complete, for example, might take days if not implemented efficiently. Time is precious in research, especially during a 10-week internship! That said, I make sure to be conscientious of my program's runtime. If my program appears to take longer than I expect, I assess whether there are ways to make the code more efficient.
2. One Success
I am happy to say that I have been taking a greater leadership role in my research! One area in which I noticed this development is constructing my poster for AGU. By brainstorming ideas for figures and outlining the flow of my talk, I took initiative in figuring out how to best present my research. I am furthering my scientific leadership by writing a manuscript of my project. I am doing my best to take the lead in writing this paper, and I hope to publish this work in a scientific journal!
Below is a map of Africa, the continent I am studying for my research. My map, created using MATLAB's mapping toolbox and annotated in Google Drawings, shows the outlines of Africa, its major cratons (Globig et al. 2016), and southern Eurasia. In addition, the locations of seismic stations I aim to incorporate into my project are shown as red circles. My research focuses on Africa, specifically its lithosphere, because it can reveal much insight about Earth's crust (Fishwick & Bastow 2011). After all, the African lithosphere contains many geological features of interest, including the East African Rift System (Chorowicz 2005) and cratons (Begg et al. 2009; Jessell et al. 2016). Moreover, a current lack of seismic instruments in several areas further motivates our need for geophysical study (Fishwick & Bastow 2011).
Stay tuned for more updates!
Chorowicz, J. (2005). Journal of African Earth Sciences, 43, 379–410. doi: 10.1016/j.jafrearsci.2005.07.019
Begg, G.C. et al. (2009). Geosphere, 5, 23–50. doi:10.1130/GES00179.1
Fishwick, S. & Bastow, I.D. (2011). Geological Society, London, Special Publications, 357, 343–371. doi:10.1144/SP357.19
Globig, J. et al. (2016). Journal of Geophysical Research: Solid Earth, 121, 5389–5424. doi:10.1002/2016JB012972
Jessell, M.W. et al. (2016). Precambrian Research, 274, 3–24. doi:10.1016/j.precamres.2015.08.010
This week, I have been asked to construct an elevator speech about my project. In case you are not familiar, an elevator speech is a brief, 30-60 second overview of my research, describing what I am doing and why my project is significant. Moreover, these speeches are geared towards audiences new to my project, or even geophysics itself. The goal is to get the attention of as many people as possible, so that they would be interested in hearing more about my research.
Constructing my elevator speech was pretty challenging. I have done similar exercises before. Namely, for past research internships, I prepared talks about my work geared towards an audience unfamiliar with my field. However, while those talks were ~10 minutes long, my elevator speech is much shorter. Knowing which details to include or not include became very important. As I composed my speech, I asked myself repeatedly: "What do I need to say to ensure a coherent 'story'?" Narrowing down the right details and explanations was definitely difficult. After composing a few drafts, I practiced my speech to my friends and family, and received constructive feedback.
Though challenging, I am glad to have had this experience. After all, successfully building elevator speeches will be a crucial part of my career. As a researcher, I will spend a significant amount of time at conferences, presenting and discussing my work with fellow scientists. Often, I may be presenting to people outside of my field. As such, my presentation cannot be filled with excess technical terms or jargon. What I say might be understood by a fellow seismologist, but not necessarily to an oceanographer or a geobiologist. If my presentation is not clear to everyone or if it does not get others' attention, then that defeats the purpose of presenting! By constructing elevator speeches, I practice tailoring my presentations appropriately to my audience.
I will update and polish my elevator speech as my internship progresses. I am very excited to present it at AGU this fall (and hopefully other conferences!), as well as to my classmates, professors, and research group back at Princeton.
Wow, I can't believe it's already my third week. Time certainly flies! This week, I have been asked to share with you (a) a description of the data I will use for my project and (b) a reflection on a research skill I intend to build.
(a) My project data
As you read in my project description, my objective is to build tomographic maps, showing the velocities of surface waves across Africa. To construct these maps, I will be using records of surface waves, collected by seismometers throughout the continent. I, however, will not be seeing these records directly. Instead, another student researcher in my group is processing these data. She works with these stations in pairs, and for each pair, she isolates the surface waves of interest and derives how fast they travel from one station to the next. Her results will be passed along to me. Then, using the locations of these stations, I will reconstruct how fast those surface waves travel across the continent -- and voila: a tomographic map!
(b) Some self-reflection
At the start of our summer, IRIS provided us interns with a mentoring rubric, a checklist describing a series of research-related skills. This rubric has been very helpful in reflecting my internship experiences. After all, as you read in my first blog post, I aspire to grow more as a research scientist.
In particular, two goals I am pursuing are developing a better understanding of and taking greater leadership roles in my project. How successful I am with these goals is contingent upon how well I understand my research. This understanding, in turn, depends on understanding the relevant scientific literature and my project's place within it. That said, two of the mentoring rubric's skills are especially important for me: "Explain how my research project will contribute something new to existing knowledge" and "Identify and use a range of relevant bibliographic and virtual sources related to my research." In short, fulfilling these goals means being able to explain why my project matters, in the context of what has been done in seismology. These skills are critical, to say the least, as the key of meaningful research is to produce something new --- whether that is a new finding or a new method for data collection or analysis. After all, if a project has been done before, it would not be very worthwhile for the academic community to read, or even hear about at a conference! By all means, those rubric skills are contingent to my career as a scientist, so I aim to develop these as much as I can.
To do so, I am taking several steps. For one, I set aside time to search and read scientific papers relevant to my project. To find sources from reliable, academic publishers, I input key words related to my project, such as "Africa tomography" into Google Scholar. I then read each paper carefully, annotating as I go along. I also keep notes about key points, such as how that project differs from my own. What is not addressed by that research, that my project can address? What is something new that my project can contribute? Thanks to a notetaking sheet provided by IRIS, I have been able to organize my notes so that I can easily refer to them later. In addition to the paper's contents, I also keep track of its bibliographic information using a citation manager. Citation managers have been extremely useful when I need to cite papers, especially well after I read them. So, I anticipate this resource will be very helpful as I construct my AGU poster!
As discussed in my project description, my project centers around tomography, the branch of seismology using inversion to derive a region's seismic velocities. As an aspiring seismologist, I am excited and honored to pursue this research and grow as a scientist! In particular, I am looking to build the following skills this summer:
1. Gain experience with and better my understanding of tomography
Though I am very fortunate to have had experience in seismology research, I have not yet pursued a project focused on tomography. As such, I am very eager to dive into this project! By the end of summer, I will have (hopefully!) constructed and analyzed tomographic maps of Africa. As I work towards this objective, I hope to build a more solid understanding of my project, as well as tomography in general. More concretely, my goal is to be able to answer questions about my project --- such as its background, methods, and significance to seismology --- in a clearer, more confident way. Discussing my project with my mentor, research group, and fellow interns, will let me measure how far my understanding progressed. Having a thorough understanding of my project becomes especially important when I present it, whether it is at a research group meeting, a scientific conference, or through a publication. Presenting my work is a crucial part of being a scientist, so I am eager to improve as much as possible.
2. Take a greater leadership role in my project.
As the summer progresses, I also aim to take increasingly greater leadership roles in my project. This goal is of particular interest to me, as it is relevant to my career development as a researcher. As I progress through this path, I will take more ownership over my work and have greater agency in deciding where to go next --- which methods to use, how to analyze my results, which research questions to answer, etc. This internship, where I will work closely with a research question, will be the perfect environment to start building this skill. By the latter half of my summer, I aim to take more initiative in proposing the directions of my research, especially compared to now.
3. Improve my programming skills
Through my previous research experiences, I gained experience in programming languages important for seismology. For example, I learned how to use MATLAB and Seismic Analysis Code (SAC) to process seismic data. However, there is always room for improvement. For example, there are programming tools out there that I have not yet used, but will learn through this internship. Right now, I am learning how to use rj-TOMO, a software designed for performing inversions on seismic data. I am operating this code on problems using synthetic, as opposed to real, data and writing programs to visualize these results. I aim to learn how to use these programs on real data soon! Moreover, I look forward to furthering my experience with programming languages, such as Python and MATLAB, and growing as a programmer.
I will be sharing more of my progress as the weeks go by. Stay tuned!