20-24. Applications of full-waveform inversion for high-resolution seismic velocity models and site response in support of earthquake ground motion investigations

CLOSED

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Ground motion characterization represents one of the greatest uncertainties in probabilistic seismic-hazard analysis. While advances in 3-D ground motion simulations are prompting their serious consideration for inclusion in next-generation seismic-hazard models (Moschetti and others, 2018), many important scientific issues affecting accurate ground motion prediction remain. First among them is development of robust high-resolution seismic velocity models, which is a critical step for characterizing subsurface geologic properties and understanding anelastic wave propagation caused by both path and site effects. Over the past 15 years, full-waveform inversion (FWI) has become a routine tool in earthquake seismology parallel to advances in computational resources and numerical methods from crustal (i.e., sedimentary basin) to global scales providing high-resolution images in densely instrumented and seismically active regions. However, even with the emergence of ambient noise and microtremor array techniques and advances in noise FWI theory for obtaining shear-wave velocities, there are very few studies to date using these data in an FWI framework due to adverse effects of, for example, uneven source distributions and measurement techniques on the resolution of tomographic models. Thus, there is a need to explore both state-of-the-art ambient noise and multi-method (both active- and passive-source) high-frequency multi-component datasets with FWI for characterizing earthquake wave propagation phenomena such as basin-edge effects, converted phase generation, attenuation, and site response.

Scientific questions influencing the ability to numerically model earthquake ground motions may be broadly separated into questions about the earthquake rupture and questions about the seismic structure (path and site effects) of the Earth. The focus of this Mendenhall Research Opportunity is to explore application of FWI methods for creating velocity, density, and attenuation models that support understanding of earthquake wave propagation in regions of high seismic hazard and societal impact, leading to improved prediction of earthquake ground motions. The higher-resolution seismic structures of basins will also allow for better characterization of finite-source effects.

The primary regions of interest motivating our interest in this research opportunity include the Wasatch Front, Utah, the Mississippi Embayment and Atlantic and Gulf Coastal Plains, the Pacific Northwest, and Cook Inlet, Alaska, though other high risk areas will be considered. While highly disparate tectonics exist in these regions, the seismic hazards from earthquake ground shaking are poorly understood because of the relative paucity of ground motion recordings and the effects of complex 3-D seismic velocity/geologic structure on earthquake ground motions. Our primary research targets are highly urbanized areas that sit atop deep sedimentary basins that amplify and prolong strong ground shaking. There may be opportunities to acquire new data in support of the applicant’s proposed FWI research (for example, for new site characterization) as part of the proposal process. In addition, the USGS anticipates acquisition of multiple nodal array datasets (e.g., New Madrid Seismic Zone; Anchorage, Alaska) that could be used in support of this opportunity. Similarly, the USGS has pre-existing active-source site characterization data in select regions, as well as access to newly acquired community datasets (e.g., in the Pacific Northwest), that would be ideal test cases for FWI analysis. Finally, depending on the research area, earthquake time-series data might be available for inclusion in FWI.

We seek a postdoctoral candidate to conduct research on problems that utilize full-waveform inversion to resolve seismic structure in regions of importance for characterizing earthquake ground motions and improving estimates of seismic hazards. The research effort will be largely determined by the postdoctoral fellow’s background and interests but ideally will broadly align with our interests in seismic hazards in the United States including the Wasatch Front, Utah, the Mississippi Embayment and Atlantic and Gulf Coastal Plains, the Pacific Northwest, and the Cook Inlet region of Alaska.

A wide range of research questions may be explored, including but not limited to:

• developing high-resolution seismic structure from full-waveform inversion of earthquake records and ambient noise data; and
• improvement of seismic model resolution through full-waveform inversion of seismic site characterization data for estimating site response.

Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.

References:

Bozdag, E., Peter, D., Lefebvre, M., Komatitsch, D., Tromp, J., Hill, J., Podhorszki, N., and Pugmire, D., 2016, Global adjoint tomography: first-generation model, Geophysical Journal International, v. 207, p. 1739–1766.

Brittan, J. and Jones, I., 2019, FWI evolution –– From a monolith to a toolkit, The Leading Edge, Special Section: Full-waveform inversion, v. 38, p. 179–184.

Moschetti, M.P., Luco, N. Frankel, A.D., Petersen, M.D., and others, 2018, Integrate Urban-Scale Seismic Hazard Analyses with the U.S. National Seismic Hazard Model, Seismological Research Letters, v. 89 (3), p. 967­–970.

Sager, K., Boehm, C., Ermert, L., Krischer, L., and Fichtner, A., 2019, Global-scale full-waveform ambient noise inversion, Journal of Geophysical Research, v. 125, 17 p.

Tran, K.T., Mirzanejad, M., McVay, M., and Horhota, D., 2019, 3-D time-domain Gauss–Newton full waveform inversion for near-surface site characterization, Geophysical Journal International, v. 217, p. 206–218.

Proposed Duty Station: Golden, Colorado

Areas of PhD: Seismology, geophysics, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet the qualifications for one of the following: Research Geophysicist or Research Physical Scientist.

(This type of research is performed by those who have backgrounds for the occupations stated above.  However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Human Resources Office Contact:  Sinar Santillano Oliveros, 303-236-9585, ssantillanooliveros@usgs.gov