My research in seismology focuses on using waves propagating from earthquakes to constrain seismic structure in order to understand processes in deep planetary interiors. Advancing this work requires theoretical seismology, while interpreting the models requires integration of geochemical studies, laboratory mineral physics, and geophysical flow modeling.
My publication and funding record reflects three major areas of research. 1) I generate new models of Earth structure on both global and regional scales in order to understand dynamic processes by analyzing large datasets of seismic observations. 2) I develop new theoretical tools to improve our ability to illuminate deep Earth structure. 3) I extend techniques to handle the challenges of interpreting future data from planetary bodies beyond Earth.
I develop widely used and cited global-scale tomographic models of the seismic structure of the Earth's mantle, the rocky layer of the Earth below the crust which makes up ~85% of the Earth's volume (e.g. Panning and Romanowicz, 2006; Panning et al., 2010; Tomography page). Seismic tomography is a technique analogous to medical imaging using waves from earthquakes recorded at seismic stations around the globe in order to map 3D structure of the Earth. Advances in this field since its inception have permitted images of increasing resolution, and the addition of more detail through the imaging of anisotropy of seismic waves (the focus of much of my research). Anisotropy is the directional dependence of seismic velocities, and it is direct evidence of dynamic processes in the Earth. This research has led to high-impact conclusions about dynamics in the top (Gung et al., 2003) and bottom of the mantle (Panning and Romanowicz, 2004). Recently, I've focused on regional scales, applying theoretical approaches I've developed to model southeast Asia (Panning et al., 2012), and using a different kind of data called splitting intensity recorded on dense North American instrumentation (Hongsresawat et al., 2015).
My research program also focuses on creating new theoretical tools to model seismic data. I have developed 3D sensitivity kernels for anisotropic structure that can be more directly compared with flow modeling results (Panning and Nolet, 2008), tools to correct the use of popular 3D sensitivity kernels for seismic waveforms (Panning et al., 2009), and an efficient approach to correcting for the effects of the complicated crust of the Earth when trying to image deeper structure (Lekic et al., 2010). On local scales, I have also been working on a new approach to exploit background noise to determine crustal structure in more detail (Panning et al., in preparation, 2015), which has illuminated diffuse energy repeatedly scattering from prominent geologic features in Idaho and Oregon.
The final major topic of my research is applying seismic techniques to other planetary bodies. I have developed numerical models for likely seismic signals on Europa, a moon of Jupiter with a global liquid ocean beneath an icy surface. This work (Cammarano et al., 2006; Panning et al., 2006; web page) demonstrated that surface waves could be used to determine the thickness of the ice shell (a primary goal for any study of Europa) with measurements from a single site. I was also invited to be a co-Investigator for the NASA InSight mission, scheduled to launch in March, 2016. This ~$450 million mission will land a geophysical instrument package on Mars, including seismometers and several other instruments. This will, for the first time, give us data to tightly constrain the interior structure and evolution of another planet in our solar system. In advance of the landing in 2016, we are preparing for the challenges of determining structure from a single seismic station, as compared to the extensive networks available on Earth (Panning et al., 2015).
In the near future, I intend to continue work along all 3 avenues of research. I am working to produce a high-resolution anisotropic model of North America using the splitting intensity dataset combined with other seismic data, which will likely be widely used by researchers with interest in North American tectonics. I will also focus on further developing the noise scattering technique and applying it to new areas where dense datasets are available. Finally, with the landing of the InSight mission imminent, much of my work in the near future will be focused on taking advantage of this historic dataset. High impact studies describing the detailed interior of another planet in our solar system for the first time are likely outcomes.