Ongoing and Recent Research Projects
- Seismic anisotropy in subduction zones: The occurrence and character of shear wave splitting is subduction settings is highly variable and this variety has proven difficult to explain. Characterizing anisotropy in different regions of subduction systems worldwide (including the overriding plate, the mantle wedge, the slab, and the sub-slab mantle), with the aim of determining the dominant properties of the global subduction zone flow field, has been a long-term interest of mine. Former Ph.D. students Karen Paczkowski, Erin Wirth, and Colton Lynner worked on various aspects of subduction zone anisotropy, and current Yale student Annie Haws is carrying out a minor discourse project aimed at understanding seismic anisotropy and the distribution of hydrous minerals in the Central American subduction system.
- Anisotropy and flow at the base of the mantle: Observations of seismic anisotropy in the D” region are abundant, but the origin of this anisotropy is not well understood. We have tackled this problem from both a theoretical and a computational approach, and are collaborating with mineral physicists and geodynamicists to understand how to characterize mantle flow from seismic anisotropy measurements. Former postdocs Xiaobo He, Heather Ford, Andrea Tesoniero, and Miriam Reiss contributed to this work, and former Ph.D. student Neala Creasy made lowermost mantle anisotropy the focus of her thesis. Current Ph.D. student Jonathan Wolf is working on lowermost mantle anisotropy, using both computational and observational tools.
- Shear wave splitting tomography: The development of SKS splitting tomography methodologies has been a long-term interest of mine, going back to work done as part of my Ph.D. thesis at MIT. Recently, Ph.D. student Puskar Mondal has been working on the development and application of probabilistic finite-frequency SKS splitting intensity tomography approaches. This method has been applied to data sets from Cascadia, the central Appalachians, and South America, and we are currently working on the joint inversion of SKS splitting and surface wave data sets.
- Evolution of continental lithosphere beneath the New England Appalachians: The New England Appalachians offer a natural laboratory to understand the effects of subduction, terrane accretion, and continental rifting on the evolution of the lithosphere. The SEISConn experiment, a deployment of 15 broadband seismometers across Connecticut, is providing high-resolution imaging of the crust and upper mantle. Former undergraduate student John Aragon worked extensively on the SEISConn project, and current Ph.D. student Yantao Luo is using SEISConn data in his thesis work. We are collaborating with geologists, including Yvette Kuiper and Paul Karabinos, to integrate our geophysical images with geological constraints. A new project, the New England Seismic Transect (NEST) experiment, is deploying instruments across western Massachusetts and eastern New York, as well as across Vermont, New Hampshire, and Maine, to probe the structure of the crust and upper mantle. In collaboration with Paul Karabinos and Vadim Levin, we are studying how past tectonic events have shaped this structure, as well as how relatively young processes such as mantle upwelling have modified the structure of the continental lithosphere at the passive margin.
- Structure and dynamics of the crust and mantle beneath the Central Appalachians: The MAGIC project investigated the mantle dynamics, lithospheric structure, and topographic evolution of the southeastern US in collaboration with Maggie Benoit, Scott King, Eric Kirby, and Rob Evans. We deployed a seismic and magnetotelluric array across Virginia, West Virginia, and Ohio between 2013-2016. Major findings from the project include evidence for lithospheric loss beneath the central Appalachians, the identification of a major mid-crustal feature beneath Ohio that likely corresponds to the Grenville deformation front, and the discovery of a sharp transition in lithospheric anisotropy across the MAGIC array. Former undergraduate John Aragon worked on the MAGIC experiment and made SKS splitting beneath the MAGIC array the focus of his senior thesis. Work on the MAGIC data is ongoing; for example, current Ph.D. student Ved Mittal is working on characterizing the asthenospheric mantle beneath the MAGIC array.
- Seismic anisotropy and deformation of continental lithosphere: Observations of seismic anisotropy in continental settings can shed light on past deformation processes and can help us to understand the origin of enigmatic structures such as the mid-lithospheric discontinuity (MLD). We have been working to understand anisotropic layering in continental lithosphere, particularly beneath North America. Former postdoc Heather Ford and former Ph.D. student Erin Wirth were involved in various aspects of this research.
- Mantle dynamics of the Cascadia subduction zone: My interests in Cascadia were piqued by the High Lava Plains project, a multidisciplinary effort to understand the origin and tectonic evolution of Oregon’s High Lava Plains. I was involved in the HLP project as a postdoc, and have continued to work on the mantle dynamics and evolution of the Cascadia subduction system. Recent work in Cascadia has included the application of SKS splitting intensity tomography and a review paper on mantle flow and slab segmentation.
- Flat slab subduction beneath Peru: Along with Lara Wagner and Susan Beck, I was involved in a project funded by NSF-Geophysics to deploy 40 broadband stations above the flat slab in Peru to study the causes and consequences of flat slab subduction. The deployment, known as the PULSE array, took place over approximately two and a half years and began in late 2010. We used seismological data to address two key questions about flat slab subduction that remain unanswered: 1) How do flat slabs form? and 2) What are the effects of flat slab subduction on the overriding continental lithosphere? We are particularly interested in characterizing seismic anisotropy and mantle flow in detail in a flat subduction system and using these measurements to understand the dynamics of flat slabs. Former Ph.D. student Caroline Eakin made the PULSE data the focus of her thesis.