In the 4 year period of this grant, PI Garnero and his group at Arizona State University are employing seismological analyses of Earth structure that relate to important questions on Earth's internal chemistry and dynamics. Using broadband and short period array data, investigations are centering on the deep mantle and core mantle boundary region, as well as the upper mantle and transition zone regions. Data are being characterized by direct waveform analyses, as well as by stacking and migration experiments. Wavefom and travel time data are modeled by a number ray tracing and waveform synthesis methods. The group's recent high resolution imaging of the upper mantle transition zone (TZ) and discontinuity structure beneath Hawaii and South America is being bolstered by dense data coverage in other geographic regions. Upper mantle discontinuity topography is showing a strong correlation with surface tectonics. Deep Earth research is centering on high resolution analyses of D" discontinuity structure and how it relates to the post-perovskite hypothesis, ultralow velocity zone structure and how it might relate to large dense thermochemical piles and plume initiation, and further resolution of the nature of the large low shear velocity provinces, namely beneath the Pacific Ocean and Africa. Short-period precursors to PP have been attributed to reflections off of deep slabs (to 1000 km) beneath SW Pacific subduction zones. Analyses underway involve much larger data sets, and new wavefield migration analyses to detect slab reflections at all lower mantle depths. Large data sets of outer and inner core probes are being collected. These are being used to study the outermost core, which has been characterized with reduced P-wave speeds, and properties of the inner core boundary using reflected waves, such as PKIIKP. The analyses described above are aimed at advancing abilities to form cohesive theories of Earth interior structure, chemistry, dynamics, and evolution. Further broader impacts include the support and training of a graduate student.
