19-25. Applications of full-waveform inversion for high-resolution seismic velocity models and site response in support of earthquake ground motion investigations

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, 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 emerged as a key methodology for developing these models for petroleum industry applications; although FWI has recently been employed on a limited number of problems ranging from the geotechnical to whole-earth scales, its application at the shallow crustal scale (i.e., sedimentary basin) suitable for ground motion simulations has been limited outside of industry studies. Further, 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 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 this research opportunity include the Wasatch Front, Utah, the central and eastern United States, the Pacific Northwest, and Cook Inlet, Alaska. 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 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 velocity 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 central and eastern United States, 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 velocity structure from full-waveform inversion of earthquake records and ambient noise data; and 

- improvement of velocity 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. 

Proposed Duty Station: Golden, CO  

Areas of PhD: Geophysics, seismology, geology, earthquake engineering, 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 one of the following qualifications: Research Geophysicist, 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: Joseline Martinez Lopez, 303-236-9559, jmartinezlopez@usgs.gov 

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