Description of the Research Opportunity
Subduction zones are hosts to the largest faults on Earth, capable of generating huge earthquakes and tsunamis with enormous social and economic impacts. In many subduction zones, including Cascadia and Alaska, slip downdip of these megathrust earthquakes transitions to slow, but unsteady motion on the plate interface. These slow slip events incrementally increase stress on the locked portion of the fault, with the possibility of triggering or evolving into a megathrust earthquake, but the causal relationship between these two slip modes – fast and slow – is not well understood. Nor is it understood exactly what conditions control the transition in slip modes. The significant uncertainty in how far downdip a megathrust rupture may extend implies that shaking intensities forecasted for future events may need to be revised: at major population centers along the subduction zone, the potential to experience strong-to-violent shaking may be higher than previously assumed.
Slow slip is often accompanied by an array of unusual seismic signals that exhibit longer durations and lower frequencies than typical earthquakes. Tectonic tremor, low-frequency earthquakes (LFE), and very low frequency earthquakes (VLFE) have been documented in subduction zones worldwide, including in the US. These signals mark the occurrence of slow slip and provide a tool for investigating where the fault is moving and the physics of how slip occurs.
A key opportunity for understanding the interactions between slow and fast slip in the subduction zone is research focused on the transition in behavior from the updip edge of observed tremor and slow slip into the zone where an eventual megathrust rupture is expected to occur. How is slip accommodated in this region? Recent studies have provided tantalizing new evidence about slip behavior within this transition, with the identification of large VLFEs in this transition zone in Cascadia using far-field seismic data and local strain data. These events were dynamically triggered by a distal magnitude 6.9 earthquake and may be causally connected to a subsequent 1.5-month slow slip event downdip. Slip here presents new opportunities to investigate relationships between slip modes and the physics of fault motion in the transition zone. But so far, our observations remain limited, and more systematic analysis is needed to develop our understanding.
The focus of this opportunity is to investigate the transition from fast to slow slip to improve our understanding of transitional fault behavior, and the spatial, temporal and causal connection between slow slip and megathrust earthquakes. The Fellow’s work will provide a better understanding of the role of slow slip in the earthquake cycle, the transition from fast to slow slip along the fault interface, the properties of the interface that may control slip modes, the stationarity of slip modes, and the spatial gap between the locked and tremor-generating portions of the fault. We encourage candidates to propose novel approaches for characterizing slip at the transition, which could include new techniques for detecting and locating associated seismic sources and their associated crustal deformation or examining transitions in slow slip characteristics near the updip edge of this zone. Proposals are encouraged to focus on the Cascadia and/or Alaska subduction zones, and could include leveraging existing tremor, LFE and VLFE catalogs; seismic imaging data, interrogating onshore and offshore seismic and pressure data; combining GNSS or strain data with seismic observations, and other relevant approaches.
For this project, we seek a postdoctoral Fellow who has expertise in subduction zones, slow slip and slow slip seismicity. We anticipate this project will center around analysis of seismic and strainmeter data, and inclusion of other datasets certainly may be appropriate and is encouraged. Examples of available data are GorDAS, PANGA & NOTA GNSS arrays, NOTA borehole array (strainmeter & geophone), the PNSN catalog, and OBS or other seismic/node deployments.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
Proposed Duty Station(s)
Moffett Field, California
Seattle, Washington
Vancouver, Washington
Anchorage, Alaska
Areas of PhD
Geodesy, seismology, geophysics, marine geophysics, Earth science, mathematics, computer science, 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
(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.)
