2017 IRIS Undergraduate Interns

The primary object of the the project is improving understanding of subducting Tonga slab geometry by analyzing intermediate depth (70 - 300)km earthquakes. The project will specifically be focused on PS and SP waves converted at the slab surface. Precise location of the slab geometry will allow for better thermal models of the slab surface leading to better understanding intermediate-depth seismogenesis.

Shear wave splitting analysis is a common method used by geophysicists in studying structural seismology. The main purpose behind shear wave splitting is to study anisotropy present at the core-mantle boundary (CMB) as shear waves travel through the outer core and split up into their different radial and transverse components in the mantle. The splitting of the P-to-S converted phases along the CMB will have a specific polarization that can aid in determining the splitting parameters such as polarization direction of the fast wave and the splitting time between the fast and slow waves. The purpose of this study is to identify any anisotropy present at the CMB beneath Alaska where the Pacific plate is subducting underneath the North American plate. Project is funded by the National Science Foundation.

Over the period of one month, vertical and three-component seismic sensors recorded a large, underground, chemical explosion, hammer shots and ambient noise as part of the Source Physics Experiment (SPE). The ultimate goal of SPE is to produce a robust model which characterizes low yield nuclear tests to help discern these tests from other seismic activity. I will be working on creating an energy attenuation model using data from a portion of phase I (sources in hard rock geology) of the experiment. As of now, the method will be to use MATLAB to identify and measure variations in amplitude and frequency shifts recorded by the array during the experiment. I will then use these measurements to perform inversions which will yield a 2D (and possibly 3D) attenuation structure of the events. My work will then be combined with that of others working on the SPE to update and refine predictive models produced prior to data collection. The integration of predictive modeling and experimental data collection is what makes SPE unique from other experiments with a similar purpose.

Using three-component rotational and translational seismometers, we hope to generate a scattering map across an underground nuclear collapse chimney and determine the relationship between the degree of scattering and the location of the wavefront path relative to the chimney location.

Characterizing how well distributed acoustic sensing (DAS) data can monitor the movement of hydrothermal fluids associated with the enhanced geothermal system at Brady's Natural Lab, and comparing this to traditional seismic data. I will expand this after talking to Whitney this week. It sounds like we may be adjusting a fair amount of the project...

My research focuses on constraining the degree of thermal variability a seismometer can experience before sensor output and sensor self-noise get driven off scale. Through this, we hope to better understand best practices for sensor installation to limit thermal noise sources.

The goal of this project is to compare Moho depth results using the relatively new method of Virtual Deep Seismic Sounding (VDSS) with the traditional P-wave receiver function method results using the records from Yellowknife Array in Canada. The VDSS method uses teleseismic S-waves that convert to P-waves when they encounter the free surface in the region of the array. These P-waves reflect back downward, and then reflect up again from the Moho where they are detected. Thus they look like a P-wave source from the surface, but are actually from 1000's of km away, hence the name virtual. These two methods can produce different measurements of Moho topography and the aim of this research is to understand where the discrepancy is coming from.

Global tomography is a well-known technique used to probe the interior of the Earth; the images it generates have powerful use within Geodynamic models of large-scale Earth Processes, such as mantle convection and the subduction process. Over the last few decades, developments in computational power have helped create a range of tomographic models that have highlighted robust features within the interior of the Earth. However, these models may disagree on several key parameters, such as the values of elastic moduli within the Earth's Interior; this may in part be due to the fact that different global tomographic models draw upon different wavelengths to probe deep Earth structure. Here, I compare these models using a range of methods to understand where they differ, as part of a larger effort working towards a full, 3-D Reference Earth Model.

The Cascadian Subduction Zone (CSZ) is an interesting location as there are very few detected earthquakes. Most subduction zones, like the one in Japan and Chile, have many large earthquakes reaching magnitudes of 9.0 and higher. Thus, the CSZ has been a site of intense study. Previous studies have suggested that the boundary is most likely segmented along-strike, however, variations in frictional conditions in the CSZ fault zone are not well known. Recently oceanic seismometers were placed over and around the plate interface and seismogenic zone on the seafloor. This data set, called the Cascadian Initiative Amphibious Network, provides more data for events that can't be detected by land-based seismometers. I will be using a subspace detection method (SDM) to find new events that are occurring on the CSZ through the data collected by the sea-floor seismometers. SDM uses a family of templates to better detect and match new events. I will then remove any potential events not seen as a real event by visually inspecting the results. Following this, I will attempt to locate the earthquakes to discern if they occur on the megathrust zone or on smaller faults. If they occur on the megathrust the locations will inform us where seismic patches are, improving our understanding of the plate boundaries heterogeneity. (Edit: I will no longer be locating events. Due to time constraints, events will be located after I leave NMT)

Ground Motion Prediction Equations (GMPEs) are empirical equations used to estimate ground shaking from an earthquake. GMPEs are essential for seismic hazard analysis so it is important to reduce uncertainties in the equations in order for predictions to be as accurate as possible. GMPEs include source, path, and site terms. This summer, I will investigate how the path terms correlate with t*, a seismic attenuation parameter which measures how much high frequency energy decays over the path. The goal is to see if incorporating a t* term into the GMPEs reduces the error.

This summer, I will be working with a research group at the Australian National University using ScS-S travel times to image the core-mantle boundary (CMB), using a Bayesian framework and data recorded in Australia. The aim of this project is to characterize heterogeneities in the lowermost layer of the mantle, which includes partial melting, anisotropy, and thermal and chemical heterogeneities.

I'll be analyzing six months of waveform data from Northern Oklahoma in order to compile a catalog of local earthquakes during that time period. The goal is to better understand the sources and processes associated with induced seismicity in the region.

I'm working at the University of Washington, studying Mount St. Helens, using data collected from the iMUSH project with Dr. Erin Wirth. (check out imush.org for more information!) We're going to perform a shear-wave splitting analysis on the seismic data, with the hopes of determining the state of deformation and strain of the mountain.

Although the title is self explanatory, here's a little detail of my project: I have to figure out the source of some of these unusual seismic activity. What motion gave rise to the EQ's, figure out where the EQ has happened and then break them into categories like biological, volcanic, , or local EQ's.