Description of the Research Opportunity
Subduction zones host some of the largest geologic hazards on Earth, capable of generating huge earthquakes, tsunamis, and submarine landslides with enormous social and economic impacts. These hazardous phenomena also occur in other tectonic environments, so insights about these processes have broad implications. While not directly hazardous, slower deformation processes (evolving over hours to months or longer) impact the potential for short-duration (seconds to hours) ones and must be understood to accurately assess hazards and issue meaningful forecasts. In subduction zones, accommodation of relative plate motions via fault slip occurs largely offshore. However, most geophysical observations are from onshore, and the distance between them and the slip events has resulted in large uncertainties in resolving subduction zone deformation processes. The needs motivated by these offshore geologic processes may potentially be filled by innovative seafloor observations of spatially dense measurements with sufficiently high temporal sample rates and long durations. One major challenge in using these observations arises from the overlying ocean and marine life, which create a plethora of signals that may be difficult to distinguish in most geophysical and geomorphic data; e.g., nearly identical seismic signals may be produced by T-phases (distant earthquake-generated waves that travel largely in the water column), submarine slope failures, or tectonic tremors (Gomberg et al., 2021). These complex processes may be distinguished by combining multiple data types, with one exciting new possibility arising from the use of distributed acoustic sensing (DAS) to create dense virtual arrays on the seafloor with fiber optic cables. This may utilize existing unused seafloor cables (‘dark fiber’; see Romanowicz et al., 2023) or new ones, along with seismic, hydrophone, pressure, and temperature sensor networks (herein called OBS, or ocean bottom sensor deployments). This Research Opportunity focuses on, but is not exclusive to, the use of existing datasets and infrastructure, particularly dark fiber DAS to investigate its potential when used with complementary data and models for probing questions about seismic and aseismic deformation in offshore subduction zone settings.
An example of a significant scientific advance this Research Opportunity may tackle would be confirmation of the existence or lack of aseismic slip transients up-dip of the presumed seismogenic region of the megathrust. In the Cascadia subduction zone, the transients down-dip of the seismogenic region are well documented owing to their proximity to the accessible terrestrial measurement sites. Observations of offshore transients have been elusive but whether they occur and their characteristics if they do, may be elucidated using multiple observation types. The latter include geodetically measured seafloor strains using DAS or more common absolute pressure gage recordings, seismic signals from tremor and other ‘low frequency’ earthquakes, repeating earthquakes, and swarms, measured using DAS, OBS, or cabled sensor data. Tackling this and other explorations will require characterization of the ranges of event sizes, frequency contents, and durations of signals that seafloor DAS can detect and reliably record and developing approaches to discriminate the multitude of tectonic and non-tectonic signals using multiple types of seafloor data.
Research focused on the Alaska and Cascadia subduction zones is encouraged, but studies focused on areas outside Alaska and Cascadia will be considered if appropriate to advancing the research goals. Potential existing and available datasets from U.S. subduction zones include those from the Alaska Amphibious Community Seismic Experiment and Cascadia Initiative OBS deployments, the Cascadia Ocean Observatories Initiative (OOI) and NEPTUNE cabled observatories offshore the U.S. and Canada respectively. Offshore DAS datasets include that from the SeaFOAM experiment (Romanowicz et al., 2023), and experiments the Research Opportunity mentors have participated in along the OOI cables off Pacific City, Oregon and in the Cook Inlet of Alaska. If advantageous, datasets from elsewhere also may be used.
We seek an individual with background and interest in geodesy, seismology, and data science to pursue research on seafloor deformation in subduction zones. In addition to the frontier nature and the novelty of fusing multiple seafloor data types, advances in analysis techniques should be utilized to expand our understanding of deformation processes. Development of machine-learning methods is encouraged, including unsupervised learning approaches when large, validated, linked observation-to-process datasets do not exist, as well as supervised learning when they do.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
References
Gomberg, J., Ariyoshi, K., Hautala, S., & Johnson, H. P. (2021). The finicky nature of earthquake shaking-triggered submarine sediment slope failures and sediment gravity flows. Journal of Geophysical Research: Solid Earth, 126, e2021JB022588. https://doi.org/10.1029/2021JB022588
Romanowicz, B., R. Allen, K. Brekke, L. Chen, Y. Gou, I. Henson, J. Marty, D. Neuhauser, B. Pardini, T. Taira, S. Thompson, J. Zhang, S. Zuzlewski; SeaFOAM: A Year‐Long DAS Deployment in Monterey Bay, California. Seismological Research Letters 2023; https://doi.org/10.1785/0220230047
Proposed Duty Station(s)
Woods Hole, Massachusetts
Vancouver, Washington
Seattle, Washington
Moffett Field, California
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 or Research Geologist
(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.)
