Collaborative Research: Towards improved imaging of the outermost core through determination of the effects of lowermost mantle heterogeneity and anisotropy

Project: Research project

Project Details

Description

The outermost core thus holds important clues to the dynamical and chemical evolution of the entire interior and receives attention across geo-disciplines, especially due to seismic evidence suggesting stratification from reduced P velocity in the outermost 50-150 km. Imaging this region requires measurement of core waves which are also sensitive to lower mantle heterogeneity and anisotropy. Here, we propose to investigate travel time, wave path, waveform and shear wave splitting anomalies of SmKS core waves used to study the outermost core. To accomplish this, we introduce a method that builds geographically localized seismic sub-arrays which permit array analyses of the wavefield, and a stacking method that makes an array beam time series for each sub-array. Beamed data have improved signal to noise ratios and will be used in heterogeneity and anisotropy measurements. 3D wavefield synthetics are used to benchmark how 1D outer core imaging tools are affected by mantle heterogeneity. Outermost core seismic models will subsequently be determined in forward and inverse experiments based on best and corrected data.
Intellectual Merit. The outer core and its detailed structure have connections to and impact across geo-disciplines. For example, the outer core relates to the magnetic field, heat flow from the core to the mantle, and core mantle chemical processes. Thus the detailed nature of the outermost core relates to fundamental behaviors of the planetary interior. However, studying the outer core requires analysis of seismic data that propagates through the lowermost mantle, which is the most heterogeneous region in the Earth deeper than the upper mantle. This proposal aims to document, understand, and mitigate the effects of heterogeneity and anisotropy that affect these data, to minimize their contributions to outer core seismic imaging. The proposal combines deep Earth researchers with deep mantle heterogeneity (DF, EG, ML) and anisotropy (ML, EG) seismic imaging expertise, as well as full 3D wave propagation and inversion expertise (EB, ML). Thus, this proposal combines a team of observational and computational seismologists to best accomplish the goals.

Broader Impact. This project will support one undergraduate summer intern through the SURF (Summer Undergraduate Research Fellowship) program at Yale, which is primarily aimed at students from underrepresented groups and fosters diversity among the student body. An undergraduate student at ASU will participate in data collection/analysis. A PhD student at each of the faculty PI institutions will be trained and collaboratively interact at yearly meetings, as well as during regular Skype meetings. Postdoc PI Frost will be mentored by the faculty PIs in training for a future faculty position, and in particular, will be involved in co-mentoring PhD students of the faculty PIs. Funding will support an early career faculty (PI Bozdag). PI Frost is active in science outreach and will continue to present research to school students and the public (https://danielafrost.com/outreach). PI Garnero will incorporate data into renderings used in the 3D Marston Theater in ASUs School of Earth and Space Exploration, which gives shows to 1000s of attendees from the general public. Any and all products of this project (e.g., new 1D outer core model, all time, slowness, and back azimuth measurements, shear wave splitting measurements, etc.) will be publicly available through web repositories. New additions and modifications to the SPECFEM3D_GLOBE package will be implemented into the developers and the official versions available through the CIG.
StatusActive
Effective start/end date9/1/208/31/23

Funding

  • National Science Foundation (NSF): $206,806.00

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