Description of the Research Opportunity
Understanding seismic hazard in detail inherently requires high-resolution information. The amplitude of peak earthquake ground motions decays rapidly with distance from faults and is strongly modified by local geologic structure. To fully quantify hazard, we require information at the scale of 10s of meters, yet the seismic networks we utilize for most studies have instrument spacings of 10s of kilometers. Several USGS earthquake products require modeling of ground motions at very fine spatial scales. For instance, both ShakeMap and ShakeAlert incorporate spatially variable models of shear-wave structure, currently at a relatively coarse resolution. Shaking at many of the sites that experience the strongest shaking is underpredicted by those models due to the limited resolution of available site amplification models. Making a leap in scale from kilometers to meters has the long-term potential to transform these key USGS products as high-resolution velocity structure may lead to improvements in the understanding of how site effects affect ground-motions and our ability to model them.
In the last 5-10 years, a revolution has started in how high-resolution information on crustal and fault structure is obtained in seismology. The use of the so called ‘dark fiber’ telecommunications cables for recording the strain field from seismic waves provides this jump in resolution to the few meters scale. In the past, collecting high-resolution information on fault geometry and seismic velocity structure required efforts to permit and carry out temporary instrument installations including the use of explosive seismic sources. In contrast, the application of the ambient noise imaging and body-wave travel time tomography techniques are particularly well suited to DAS data and provide similar scale information with only a single instrument. The ability to refine 3D velocity models that are used in seismic wave propagation simulations using DAS data is relatively untested at this point and perhaps complicated due to the non-uniform sampling of DAS data. A potential goal of this project might be to explore moving from single cable, two-dimensional velocity models to combining multiple DAS lines and merging DAS models into larger scale 3D velocity models and the associated simulations. Harnessing this high-resolution information on shear-velocity structure for improving ground-motion modeling and predictions has the potential to transform a broad range of USGS research areas and products.
Many key problems in seismic hazard involve understanding fault-zone structure at the depths of earthquake rupture such as how shallow faults in fold and thrust belts connect to the deeper plate boundary in the Cascadia subduction zone, or how strike-slip fault strands that appear to be step-overs at the surface are connected at depth, and how damage zones effect rupture propagation. DAS-based imaging methods have been used to image crustal fault zones including the discovery of previously unmapped faults. New technique development is pushing these studies deeper into the seismogenic zone in a variety of ways including migration-based imaging, high-resolution differential earthquake focal mechanisms, and local earthquake travel-time tomography. Innovative applications of these approaches or other new approaches that use DAS data to understand the structure and geometry of specific important fault-systems, could enhance our understanding of earthquake rupture potential and dynamics with implications for seismic hazard.
We seek an individual with background and interest in seismology, DAS, and computational science to pursue research on shallow structural and fault-zone imaging. Applications of DAS-derived models to ground motion prediction via 3D wave propagation simulations or seismic hazard models are encouraged. Proposals focused on technique development and the connections between fault-zone structure and earthquake rupture properties are also encouraged. New datasets can potentially be collected as part of this project using a DAS interrogator owned by USGS.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
Proposed Duty Stations(s)
Moffett Field, California
Golden, Colorado
Areas of PhD
Seismology, geophysics, Earth science, computer science, machine learning 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 Geologist, 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.)
