Sharp structures in the deep mantle:  With the advent of USArray and other dense seismic arrays, there is an unprecedented opportunity for investigating the seismic structures within the mantle. Seismic observations of phases sampling the lower mantle have suggested Ultra Low Velocity Zones (ULVZs), a possible perovskite to postperovskite related D” layer, Large Low Shear Velocity Provinces (LLSVPs), and rolling-hills of primordial material on the core-mantle boundary (CMB). Their locations and elastic properties provide essential constraints in understanding many aspects of Earth’s chemical and thermal history. Funded by the NSF Geophysics Program.

NSF CAREER Award: Slab structure and dynamics of arcuate shaped subduction zones – Studying subduction, in general, is essential to understanding the evolution of the planet.  More fully understanding the structure and dynamics of lithosphere, the relatively rigid outer shell of the Earth, subducting along highly arcuate plate boundaries will aid in constraining geologically recorded tectonic events, global plate motions, plate boundary deformation, and the role of subducted oceanic lithosphere in mantle convection.  The overarching research goal of this CAREER award is development of an improved understanding of the structural and morphological evolution of arcuate shaped convergent margins through the study of four active arcs: the Mariana, Antilles, Betic-Rif, and Banda arcs, using a range of tools, including seismological imaging and geodynamic modeling.

Banda Arc Project Eastern Indonesia is one of the least well-understood geological domains of our planet, and yet the region provides a truly remarkable location for unraveling some of the major puzzles of plate tectonics. The recent collision of the Australian continent with the active volcanic arc in the Banda region effectively captures the initiation of continental mountain building and the cessation of island arc volcanism, offering a rare glimpse into a set of processes that have shaped Earth’s evolution over geologic time.  Since oceanic subduction and subsequent continental collision have occurred in different stages along the Banda arc, we plan to use the region to study and assess the spatio-temporal evolution of this transition using a variety of methods: seismology, geodyanmics, tectonics, low-temperature geochemistry, and geomorphology.  We have installed 30 broadband seismometers, including the first ever seismometer on Timor Leste, across the archipelago of eastern Indonesia (NTT) in 2014.   The award is co-funded by the NSF Geophysics and Tectonics Programs, and the Office of International Science and Engineering (OISE) – Global Venture Fund (GVF).

PICASSO –   A large multidisciplinary, international investigation of the Alboran Sea, Gibraltar arc, Atlas Mountains and surrounding areas in the western Mediterranean using passive and active seismology, magnetotellurics, geochemistry, petrology/structural geology, and geodynamic modeling.  One aspect of the project includes imaging the lithosphere and uppermost mantle using receiver functions and surface wave tomography in combination with geodynamic modeling.  USC’s structural seismology group deployed 15 broadband seismometers from 2009-2013 in a linear array across the Atlas Mountains as part of ~100 passive source instruments used for imaging in this project (field work photos). The award is co-funded by the NSF Continental Dynamics Program.

Evolution of the Colorado Plateau using Earthscope USArray data –   We used a combination of surface wave tomography and P- and S-wave receiver functions (RFs) to clearly image the base of the crust, the lithosphere-asthenosphere boundary (LAB) across the southwestern U.S.   The use of both Ps and Sp RFs allows for independent models of the same area, and provides different frequency bands of investigation and different raypaths to image lithospheric and upper mantle structure.  Joint inversions provide better constraints on both velocity-density discontinuities (from RFs) and absolute velocity structure (surface waves).

Moho across Southern California –   A series of SCEC funded projects to determine the depth to the Moho from P receiver functions using broadband data from permanent and temporary stations across southern California.  Systematic mapping of the Moho and related discontinuities will allow for investigation of discrete faulting at depth.  The project focuses on imaging of the eastern California Shear Zone (ECSZ), the Garlock fault, and the faults of the southern San Andreas Fault (SAF) system.

Imaging the North American Craton – Delineating crustal and lithospheric interfaces within the continental lithosphere can provide important constraints for the formation of continents and the evolution of their cratonic cores.  The use of S-wave receiver functions and joint inversions with surface wave phase velocities to image the lithosphere-asthenosphere boundary and internal subdivisions within the lithosphere improves our understanding of cratonic keels and how they couple to present-day convective flow in the deeper mantle.