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The Cascadia subduction zone, extending from northern California to Vancouver Island, Canada, has a 10,000-year record of producing earthquakes of M8.5 or greater at intervals of several hundred years. The last major event, in 1700, was likely of M9, although paleoseismic data indicate that past great Cascadia earthquakes have had a range of magnitudes. But since modern seismic recording began, there have only been M<5 earthquakes on the subduction interface offshore of Oregon and Washington.
We now know there are frequent transient accelerations of aseismic slip throughout the Cascadia forearc, down-dip of the anticipated megathrust rupture. These aseismic deformation episodes, which generally occur simultaneously with low-frequency tectonic tremor beneath the coast range, are increasingly well documented by the networks of continuous GNSS stations and borehole strainmeters of the National Science Foundation-funded Network of the Americas (NOTA). Inversion methods that leverage these diverse data types could enhance understanding of the relationship of these events to Cascadia earthquake potential.
Understanding the physical processes of deformation on the subduction interface and quantifying the extent and rate of aseismic deformation is needed to assess the interseismic slip deficit in the shallowest part of the megathrust, which directly controls the potential seismic hazard of the Cascadia subduction zone. In particular, the degree of plate interface coupling between the coast and the trench is a critical unknown for estimating seismic hazard but characterizing ongoing deformation in this region is complicated by the fact that most types of conventional geodetic observations (such as GNSS and InSAR) can only be made onshore. However, surveys of GNSS-A monuments as well as seafloor pressure sensors offshore Cascadia will provide important information for constraining the temporal and spatial distribution of offshore locking. In addition, the onshore Network of the Americas (NOTA) strainmeter network may provide additional constraints on subduction zone slip above traditional geodetic observations.
We seek an individual with background and interest in geodesy or seismology to pursue research on aseismic deformation in Cascadia, ideally fusing data from the NOTA strainmeters and seafloor geodesy with continuous GNSS data from NOTA and Central Washington University’s Pacific Northwest Geodetic Array (PANGA), along with any other types of available data. There are numerous possible research topics that could help us understand the kinematics of slip in the Cascadia subduction zone, the physics of slip and tremor processes, and the resulting seismic hazard. These topics include but are not limited to: the relationship of aseismic slip events to major earthquakes; forecasting Cascadia post-seismic slip and its hypothetical implications for evolution of a Cascadia megathrust earthquake sequence; optimal utilization of strain, seafloor geodetic, and GNSS data to rapidly constrain depths and focal mechanisms of major earthquakes offshore Cascadia; and development of algorithms to detect and locate sources of aseismic deformation in near-real time.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
Proposed Duty Station: Moffett Field, California; Pasadena, California; Vancouver, Washington; Seattle, Washington
Areas of PhD: Geophysics, geology, seismology, geodesy, Earth 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 the qualifications for one of the following: Research Geophysicist or Research Geodesist
(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: Victor Mendoza, 650-439-2454, vjmendoza@usgs.gov
