Ongoing and Recent Research Projects
- Global patterns of 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. I have been working to characterize 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. Along with the late Paul Silver at DTM, we have proposed a global model (Long and Silver, Science, 2008) for mantle flow in subduction zones which emphasizes the importance of trench migration and work is currently underway to understand the implications of this model for mantle dynamics (see our 2009 JGR paper). I have recently been funded by NSF-Geophysics to collaborate with Chris Kincaid at the University of Rhode Island and Laurent Montesi at the University of Maryland to carry out numerical and laboratory models of subduction with migrating trenches to test the geodynamical plausibility of the model. Current Yale graduate students Erin Wirth and Colton Lynner and recent summer intern Kimmy McCormack have been involved in various aspects of this project. This work has been funded by NSF.
- Flat slab subduction beneath Peru: Along with Lara Wagner and Susan Beck, I have recently been 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 are using 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? I am 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. The first ten PULSE stations were deployed in late 2010 and the remainder were deployed in May/June 2011. Yale graduate student Jenny Hanna and recent Yale College grad Laura Marris spent time in Peru during fall 2010 for the first PULSE installation campaign (see Laura’s Singular Subduction field blog), and a large group of Yale seismologists (including Maureen Long, Erin Wirth, Caroline Eakin, Colton Lynner, and former student Jenny Hanna) spent time in Peru in May/June 2011 working on the deployment. Yale graduate student Caroline Eakin is working on data from the PULSE project. The PULSE stations were demobilized in June 20013, and the first batch of publications based on PULSE data are currently in preparation. Stay tuned for updates, and check out a webpage about the PULSE project maintained by Abhash Kumar at UNC here.
- Seismic structure and dynamics of the crust and mantle beneath the eastern US: I am involved in investigations of the mantle dynamics, lithospheric structure, and topographic evolution of the southeastern US in collaboration with Maggie Benoit, Scott King, and Eric Kirby. In 2009-2010, we deployed the Test Experiment for Eastern North America (TEENA), a pilot project designed to probe the structure and dynamics of the eastern US passive continental margin and to understand the connections between the surface geology and deep crustal and mantle structure. Preliminary results from this project led us to propose the Mid-Atlantic Geophysical Integrative Collaboration (MAGIC), which has recently been funded by NSF. The first stations in the MAGIC experiment were deployed in October 2013 - stay tuned for updates!
- Anisotropy in the lowermost mantle: Observations of seismic anisotropy in the D” region are abundant, but the origin of this anisotropy is not well understood. My interest in D” anisotropy was piqued by some experimental work I did several years ago with Shun Karato and others, looking at the development of lattice preferred orientation in (Mg,Fe)O and predicting the shear wave splitting patterns that would result from this anisotropy. Recently, I have begun to work on D” anisotropy from a seismological perspective, using observations of SKS-SKKS splitting discrepancies in western North America to place constraints on lowermost mantle anisotropy beneath the eastern Pacific. Ongoing work on this problem includes using a variety of raypaths to study D” anisotropy in different regions to try to place tighter constraints on the geometry and causes of the anisotropic structure, with an initial focus beneath Africa. Dr. Xiaobo He, a former Yale postdoc, worked on this project, and current Yale postdoc Dr. Heather Ford is continuing to work on this effort.
- Young tectonomagmatism in the High Lava Plains of Oregon: The HLP Project was a multidisciplinary effort funded by NSF-CD and headed by Rick Carlson to understand the origin and tectonic evolution of Oregon’s High Lava Plains. The HLP is a young, bimodal volcanic province that has produced voluminous volcanic activity over the past ~ 15 Ma, but its origins are poorly understood. I was involved with the broadband seismology component of the project, working with PIs David James and Matt Fouch. 104 stations of the HLP array operated through September 2009 in eastern Oregon, northern Nevada, and western Idaho. Projects involved understanding contemporary mantle flow beneath the HLP using shear wave splitting measurements (and other indicators of anisotropy), relating that mantle flow to the ongoing tectonomagmatism at the surface, and using these inferences to discriminate among the many models for HLP formation. I collaborated with HLP participants Chris Kincaid and Kelsey Druken to combine shear wave splitting measurements with constraints from laboratory models, and with Lara Wagner at the University of North Carolina on combining shear wave splitting measurements and surface wave analaysis to characterize upper mantle anisotropy beneath the HLP. Yale graduate students Erin Wirth, Jenny Hanna, Duayne Rieger, Brad Foley, and Patrick Young were involved in HLP field work.
- Shear wave splitting tomography: Part of my thesis research at MIT involved the theoretical development of a method for wave-equation shear wave splitting intensity tomography that incorporates constraints from geodynamical models. Ongoing work includes the implementation of this method to study the distribution of anisotropy beneath the High Lava Plains of Oregon. Collaborators on this work include Rob van der Hilst and Brad Hager at MIT and Maarten de Hoop at the Center for Computational and Applied Mathematics, Purdue University. Recent papers on theoretical aspects of anisotropy tomography can be found here and here.