Description of the Research Opportunity
The current state-of-practice in earthquake hazard analysis typically revolves around empirical ground motion models (GMMs). However, GMMs are limited in a few ways; for example, due to paucity of near-fault recordings especially for the largest events, they are constructed with very few constraints from near field sites, and they can generally only account for 1D aspects of the subsurface structure, overlooking any wave propagation or site effects from complex 3D geology. Physics-based models of ground motion, on the other hand, are not limited by these constraints, as they emulate earthquake processes by using advanced numerical algorithms that incorporate physical laws governing rupture propagation, seismic wave propagation, and ground motion amplification. Because these physics-based numerical models can be generated for any scenario earthquake at an arbitrary site, engineers would like to incorporate them into practical seismic hazard analysis.
Physics-based models of earthquake processes have existed for decades and are already quite sophisticated, but further development is crucial in relying on them to inform or supplement practical earthquake hazard characterization. This includes a range of avenues including development of realistic kinematic rupture models of scenario or historical events, improved modeling of the frictional processes and stress conditions leading to unstable fault slip, creation and maintenance of accurate 3D models of the subsurface structure, including both shallow geotechnical information as well as deeper structure, investigation and partitioning of path and site effects in this complex media, and validation of any of these facets with real data.
We seek a Mendenhall Postdoctoral Scholar to make advancements in physics-based modeling of 3D earthquake processes through existing or updated earth structure models, within the context of bettering our understanding of earthquake hazard. Relevant ideas could involve any combination of the following topics:
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Kinematic rupture modeling of real or scenario events that investigates finite source attributes (e.g., size and shape of rupture patch, slip distribution, rupture velocity, source time function, rupture directivity) and how they translate into ground motion observables (e.g., peak intensities, duration) or relate to inferred faulting characteristics (e.g., stress drop, rupture directivity).
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Dynamic rupture modeling to better understand how kinematic rupture properties (e.g., the source attributes listed in the previous paragraph) result from conditions on the fault, including fault geometry, roughness, stress state and prescribed stress drop, choice of friction law, off-fault plasticity, and dynamic pore pressure effects.
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Development of seismic velocity models or improvement of existing ones (e.g., the USGS San Francisco Bay region 3D seismic velocity model, SF-CVM). Existing models can be evaluated by comparing simulated motions with observations, or more novel approaches. Development or improvement of models could include 3D geologic modeling, seismic tomography, or site characterization with active or passive methods. Design and deployment of nodal seismic arrays is a possibility.
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High-frequency wave propagation simulations to study earthquake hazard. Empirical ground motion studies often separate contributions to measured ground motions into “source”, “path”, and “site” effects. These contributions are physically meaningful and must be more discernible in physics-based simulations, where an infinite number of observation points is possible. With modern computational resources and a plethora of real seismic data, it is possible to study these competing effects and their contributions to ground motions. The results could be used to refine or mitigate assumptions made in current GMM’s concerning the various effects.
Applicants are expected to have experience in earthquake seismology, either observationally or through simulations, and an interest in improving our understanding of physical processes leading to seismic hazard.
Due to the very collaborative nature of this proposal as part of a much larger project, interested applicants are strongly encouraged to contact the advisors early on to discuss project ideas and how they fit into the larger framework of physics-based modeling of earthquake hazard.
Proposed Duty Station(s)
Moffett Field, California
Pasadena, California
Areas of PhD
Geophysics, seismology, engineering seismology, geology, data science, computer science, statistics, mathematics, 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 Engineer, Research Civil Engineer, Research Geologist, Research Computer Scientist, Research Mathematician, Research Physicist
(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.)
