Dr. Ved Lekic has been granted the NSF Earth Sciences postdoctoral fellowship to carry out a research and education plan at Brown University. He will investigate the causes and mechanics of continental rifting, which is the process in which continents are torn apart and new plate boundaries form. The project will focus on three active continental rifts that span a variety of rates, geometries and amounts of extension, different maturity and geochemical signatures: the Rio Grande Rift, the Salton Trough, and the Ethiopian and Kenyan segments of the East African Rift. Analysis of seismic data (receiver function, tomographic, and forward waveform-modeling analyses) will be used to simultaneously map broad asthenospheric and lithospheric features as well as detect and characterize sharp interfaces such as the crust-mantle boundary, the lithosphere-asthenosphere boundary, and other features that may be related to melting or faulting. Mapping and characterizing horizontal and steeply dipping interfaces associated with active continental rifts of different age, maturity, geochemical signature and deformation parameters will shed light on the causes, mechanics and evolution of rifting. In the last four decades, the plate tectonic paradigm has tremendously enhanced our understanding of how our planet works. Yet, we are still far from understanding how tectonic plates formed in the first place and how continents can break up among multiple plates at locations known as continental rifts. This investigation will create images of structures within continental rifts that can be used to learn about the processes by which continental plates weaken and break apart and the role that Earth's deep interior plays. As such, it may elucidate the way plate tectonics arose and how it continued to operate. The educational component will be centered on two courses: an advanced seminar co-taught by Lekic and the host mentor, and an introductory course in geophysics co-taught by Lekic and a faculty member at the host institution. The advanced seminar, focused on the structure, rheology and dynamics of the continental lithosphere, will directly incorporate the questions raised and insights provided by the research. It will also provide an interdisciplinary venue in which professors, post-doctoral researchers, graduate students, and advanced undergraduates from a variety of geoscience backgrounds can learn and discuss major questions and latest findings. The undergraduate course will allow Lekic to develop, apply and evaluate a suite of active learning techniques and enable him to experiment with activities and approaches that engaging the students' diverse learning styles.
The Earth’s surface is broken up into a dozen large tectonic plates, whose motions relative to one another open and close oceans, create and destroy supercontinents, and are directly and indirectly responsible for and generating the vast majority of earthquakes and volcanoes. Sometimes, existing continental plates come to break apart through a process called "rifting" and a new oceanic basin is formed. This process broke up the Pangean Supercontinent, and is currently operating along the East African Rift system as well as the Salton Trough in Southern California. Where and how rifting weakens and breaks up a continental plate is poorly understood; in this study, we developed and applied methods that use elastic waves emitted by earthquakes (called seismic waves) to image the structure of tectonic plates undergoing rifting. Our research focused on two regions of Southern California: 1. the Salton Trough, which is currently undergoing rifting related to the opening of the Sea of Cortez; 2. the off-shore Los Angeles region, which is thought to have undergone rifting in the past 20 million years. In both regions, we were able to obtain first-of-a-kind images of the bottoms of the tectonic plates that showed that the tectonic plate – which is typically 70 km thick in Southern California – is only 40 km thick beneath the Salton through and 50 km thick beneath the off-shore LA region. Surprisingly, the plate thinned by 20-30 km over a horizontal distance of only ~50 km, meaning that the topography of the underside of the tectonic plate is far steeper than topography seen at the surface. We also used seismic waves to image the structure of the tectonic plate across the Western United States, including the Rio Grande Rift, where we did not detect any clear thinning of the tectonic plate. These results are important scientifically because they provide a completely new set of constraints for laboratory and numerical modeling of the process(es) by which tectonic plates come to break apart. Furthermore, this project afforded the principal investigator, Dr. Vedran Lekic, an opportunity to perform postdoctoral research, gain training in and practice of teaching at the college level, and present the research findings at ten different domestic and international venues.
