Global P, SV, and converted wave measurements for improved lower mantle P and S structure studies

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This proposal seeks to measure every possible observable seismic wave on seismograms recorded across the globe. Measuring all possible waves involves documenting their travel times and wave shape information. These data can then be used to bolster seismic imaging efforts of Earth's mantle which currently do not routinely use multiple bouncing or echoing of waves, especially P waves. Using these waves ensures better sampling of the entire volume of the Earth's mantle. Otherwise, the southern hemisphere in particular is poorly sampled. Better imaging of Earth's mantle is important because it allows for more accurate determination of earthquake properties as well as the dynamic convection of the interior which drives plate tectonics at Earth's surface. A complete dataset of a subset of seismic waves will allow benchmarking tomographic models of different research groups, as well as permit a more direct comparison of P and S wave models of significant heterogeneities of the deep mantle. In particular, this work will study two massive low seismic wave speed structures: one beneath the Pacific Ocean, and one beneath the Atlantic Ocean and Africa. These huge structures are the largest anomalies in the planet which are unknown in nature. Resulting models will be rendered in 3D and shared with the public via the 3D Marston Theater at Arizona State University, which regularly gives science shows to the general public. The project will also support and train two students at ASU. Training the undergraduate student will involve the creation and regular updating of a data acumen training document, which will also be shared via the web. Students will be involved in data analysis, interpretation, and writing papers to be published. Scientific renderings (e.g., models and schematics) will be shared via the PI's website, as well as via direct email.This project will measure and quantify travel time behavior of a global seismic dataset of high quality P-wave phases, S-wave phases on the SV component of motion , phases having both P and SV legs in the mantle, and depth phases of P, SH, SV, and P-SV waves. The adopted approach incorporates two novel tools recently developed: (1) empirical wavelets (EWs) are constructed from the average shape of S and P waves on an event-by-event basis, which are adaptively adjusted to match variable pulse widths prevalent in data, thus minimizing travel time estimation errors; and (2) virtual stations which are built from localized geographical bin stacks of stations for phases of interest, making measurements possible for data with event-station corridors typically too low in amplitude for confident measurements. The new seismic measurements proposed here will document travel times along with several attributes of all measured waveforms, including wave shape information (amplitude, waveform broadness, waveform misfit compared to the best fitting EW), signal-to-noise ratios (SNRs, measured multiple ways), and cross-correlation coefficients (CCCs, between phases of interest and best-fitting EWs). The investigators will measure minor and major arc data at relatively short periods (10-16 sec). The new datasets aim to improve resolution in P and S seismic imaging of the Earth's mantle, with the goal of improving understanding of the structure, dynamics, and evolution of the Earth. These data will improve wave path coverage in the southern hemisphere, be applicable to imaging studies of the entire mantle, and be made publicly available along with a recently completed SH dataset using the same methodology. The data will be used for imaging large-low velocity provinces, with a focus on comparing P and S velocity heterogeneity, which bears upon the nature of heterogeneity. This work will fund a PhD student and an undergraduate student to collect, process, measure, and review P and SV seismic data. The PI will mentor the students within a broader perspective of the multidisciplinary nature of mantle heterogeneity, particularly the dynamics and evolution of the mantle, with participation in ASU's multidisciplinary geophysics group (seismology, mineral physics, geodynamics, and planetary geophysics). All data measurements, models, and codes will be openly shared with the community via the web, as well as IRIS's tomography model portal. All measurements will be shared with the 3D Reference Earth Model project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.