Research

I obtained my PhD from the Department of Geological Sciences (now the School of Earth and Space Exploration) working with Dr. Edward Garnero at Arizona State University. My research is focused on studying planetary interiors using the tool of seismology. I am particularly interested in the seismic structure of the 410-km and 660-km upper mantle discontinuities that delineate increases in mantle density and seismic wave speeds. The depths of these boundaries are sensitive to thermal and compositional changes in the Earth, making their topography an ideal probe for internal Earth structure.

Figure 1. A cutaway plot of Earth showing the crust, mantle, core, and inner core.

Figure 2. Seismic velocities and density profiles for the Preliminary Reference Earth Model, and IASP91. Both models have jumps in velocity and density near 410 and 660 km depth.

Currently, I have been investigating mantle structure beneath the Hawaiian hotspot, a proposed location for a whole mantle plume. To image the discontinuities beneath Hawaii, I am using underside reflections off the discontinuities, which are recorded by seismometers as precursors to the seismic phase SS. I am also using several synthetic seismogram methods to model the data I have collected. Ultimately, I am interested in what the seismic structure of the discontinuities can tell us about the dynamics and composition Earth's interior, and if this knowledge can be used to understand the interiors of other planets in our Solar System.

Figure 3. SS ray path geometry. PP waves sample the discontinuities in the same way.

Figure 4. Source (dots) and receiver (triangles) geometries that sample within the box shown around Hawaii, along with a photo of the islands.

Figure 5. Reflectivity synthetics for a 75 km deep source, showing the precursor wave field. SS is aligned on zero time, and the seismic phases arriving within the precursor wave field are labeled in the bottom plot.

The depth and topography on the 410- and 660-km discontinuities is dependent upon the composition and thermal character of the mantle at these depths. This makes the 410 and 660 potential mantle thermometers and probes of chemical heterogeneity. A large amount of experimental and theoretical mineral physical data exist for the phase assemblages in the mantle, and I want to combine this knowledge with seismic observations of the mantle.

Figure 6. A cross section of the mantle is shown to the left, with the dominant minerals found at each depth. The expected depth behavior of each discontinuity is shown on the right, note that the 410 and 660 move in opposite directions; this is due to their opposite Clapeyron slopes, positive for the 410, and negative for the 660.

My research up to this point has consisted of collecting an extensive seismic data set that samples beneath the Central Pacific, and then developing a method for stacking the data to search for precursor energy. My methods utilize Fortran 90/95 codes for stacking, as well as the TauP toolkit, Seismic Analysis Code (SAC), and Generic Mapping Tools (GMT) for plotting data and making figures. These are all run locally on a Macintosh running OSX and on our group's Linux computers. My stacking codes are also designed to utilize a parallel set of machines, allowing me to run numerous stacks at once. Using these tools, I am investigating the effects of a number of parameters on the resulting stacks, such as bin size, data quality, bin geometry, mantle heterogeneity corrections, and several other variables for a variety of transition zone targets around the world.