Project Title: Receiver Function Imaging of the Crustal Structure Beneath the Alaska Subduction Zone using 400 Nodal Seismometers Institution: South Dakota School of Mines & Technology Host:Dr. Kevin Ward
The largest earthquakes and most volcanism on the planet takes place at subduction zones. The subsurface dynamics of subduction zones can be studied using information recorded at the Earth's surface. Typically, this data is limited by the density of stations at the surface or by the availability of seismic waves needed to study the subsurface region of interest. Broadband seismometers can provide a lot of temporal data, but they are usually limited spatially because they are expensive and take a long time to deploy (2 in a day would be impressive). By contrast, three-component nodal seismometers are much quicker to deploy (Dr. Ward's record is 72 in a day in Alaska!) and more cost-effective, so they can be placed closer together. However, because they are battery-powered, they can only record about 30-40 days of data. The introduction of nodal sensors to academia provides an opportunity to investigate the crustal and upper mantle structure of the Alaska subduction zone. In February and March of 2019, 400 nodal seismometers were deployed with 300 spaced 1 km apart along the Parks Highway between Fairbanks and Anchorage, allowing for seismic imaging of the Alaska subduction zone at an unprecedented scale. This project will evaluate if three-component nodal seismometers are capable of imaging a previously studied section of the Alaska subduction zone using receiver functions. For the first time, the viability of using local earthquakes to generate receiver functions from a dense nodal seismic array will be explored. Receiver function imaging is a long-established method for broadband data, but it will now be applied to the relatively new nodal seismic data.
The intern role in this project spans a wide range of activities. A highlight is the opportunity to help deploy and recover nodal seismometers in Cascadia. Although this project will not use the data collected in Oregon, the type and scale of the data used from Alaska will be similar to the Cascadia field deployment. Outside of fieldwork, I will learn the background geology and tectonics of the Alaska subduction zone as well as some new studies from the EarthScope array recently completed in Alaska. A large part of the project will be learning the receiver function method as well as working with nodal data and calculating receiver functions. Finally, as I am working in Rapid City, some time will be allocated to explore the unique geology of the Black Hills.
Project Title: How do fault friction behaviors affect Cascadia rupture propagation and ground motions? Institution: University of Michigan Host:Dr. Yihe Huang
The Cascadia Subduction Zone is around ~1200 km in length, and it has the ability to host very large earthquakes. Accurate estimations of ground motions along the subduction zone are needed in order to predict potential damage, and incorporating complex friction behaviors into rupture models can allow us to better understand said ground motions. By using strongly velocity-weakening friction behaviors to simulate ruptures in the subduction zone, we hope to have more accurate ground motion estimations than the previous Cascadia models that involved slip-weakening friction behaviors.
Project Title: Defining the Source Fault of the 1886 Summerville, South Carolina Earthquake Institution: Georgia Tech Host:Dr. Zhigang Peng
135 years ago, an unexpected ~M7 earthquake shook the Charleston, SC area. This project aims to sort through seismic data collected from 2011 - 2012 and apply deep machine learning and template matching techniques to help determine the orientation of the fault that produced the earthquake. By building a new catalog with deep learning and using the template matching system to take another look at the new catalog, we hope we can add several more data points to the existing data sets to get a clearer picture of the fault geometry.
Project Title: Developing Discrete Fracture Networks for Microseismic Applications – Applied Study at EGS Collab Institution: Pacific Northwest National Laboratory Host:Dr. Hunter Knox
Geothermal energy currently accounts for only about 0.4 percent of the total energy produced in the US each year. Yet many scientists believe it can be much greater than this. As a clean energy source, geothermal is one possible alternative to fossil fuel combustion, which is unsustainable in the long term. One obstacle preventing the scaling of geothermal is availability of reservoirs. Enhanced Geothermal Systems (EGS) is one possible solution which would allow scientists to tap into previously unavailable resources. EGS uses unconventional techniques, such as hydraulic fracking to create subsurface fractures by which hot water can more easily flow through. This project's goals are to help EGS Collab in their efforts to understand how we can use EGS to harness the vast energy available in the Earth’s warm interior.
Project Title: The Mechanics of Intermediate Depth Earthquakes: a Multiscale Investigation Combining Seismological Analyses, Laboratory Experiments, and Numerical Modeling Institution: Georgia Tech Host:Dr. Zhigang Peng
This project focuses on the study of intermediate-depth earthquakes, those between approximately 50 and 300 km depth. The collaborative research applies machine-learning and waveform-based matched filter techniques to detect acoustic emissions events recorded during high-temperature high-pressure laboratory experiments. In addition, the lab plans to derive source properties (focal mechanisms, seismic moment and corner frequencies, stress drops) and statistical features (Guttenberg-Richter a and b values, aftershock productivity and decay constants), in order to gain more insights into the failure process at laboratory scales. These results will be compared with an ongoing work at subduction zone scales beneath Japan, and can provide important constraints for numerical modeling (stress state, fault geometry, etc) done at collaborative institutions.
I will be responsible for managing the continuous waveforms recorded by broadband transducers during high-temperature high-pressure laboratory experiments. I will also apply both deep-learning and matched filter techniques to detect acoustic emissions events, and derive additional source and statistical parameters during laboratory experiments.
Project Title: Creating Phase Velocity Maps of Africa with Bayesian Inversion Institution: University of Rochester Host:Dr. Tolulope Olugboji
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)
Project Title: Investigating the effects of weather and geology on recording the seismic wavefield Institution: USGS - Albuquerque Seismological Laboratory Host:Drs. Adam Ringler & Rob Anthony
This summer I will be working at the Albuquerque Seismic Laboratory (ASL) determining how different meteorological events effect seismic noise. What started as looking at rain and hail data spring boarded the project to focus on infrasound signals across a seismic array. Some interesting features we will investigate include determining the location of a lightning strike by back tracking the sound across the array and comparing the acoustic response to the speed of sound; thus, giving us distance and direction. Another interesting aspect to be explored is how acoustic response transforms/ or doesn't transform into seismic response; i.e. are seismometers measuring ground motion because of acoustic pressure variations or is it a simple acoustic response, and if the former where and how does that transition occur? One important application will be investigating best practices for emplacement methods and emplacement materials across the array to mitigate the noise response.
Project Title: Seismic Monitoring of Debris Flows Institution: Northern Arizona University Host: Dr. Ryan Porter
Flagstaff, Arizona is a hot zone for wildfires which is not only a danger to the environment but to human life. Not only are the wildfires themselves a concern, but the effects of these natural disasters can also be devastating. The debris flow that happens after the fires end causes the destruction of vegetation due to the soil becoming hydrophobic, meaning the soil cannot absorb water anymore. Seismometers are used near the Museum Fire burn area so that the post-fire debris flow can be measured and recorded.
Project Title: Using seismic refraction to determine bedrock topography in a weathered and gneiss Institution: Clemson University Host: Dr. Brady Flinchum
The critical zone is defined as the area from the top of the tree line to the base of unweathered bedrock. This environment involves the complex interaction of rock and biological life with soil formation, hydrological networks, and geochemical processes. The role of the structure of the deep critical zone has an influence on surface processes but the amount of influence and why certain topography or features causes specific surface conditions is not strongly understood. Through the use of seismic refraction the topography of the gneiss bedrock in the Piedmont region of South Carolina will be imaged to gain better understanding of the influence of bedrock structure on subsurface and surface geology in Appalachian granitoid.