S47. Investigating the subaqueous sedimentary record of the M7.1 Anchorage earthquake

A ~47 km deep Mw 7.1 earthquake struck southcentral Alaska on 30 November 2018. The rupture mechanism, aftershocks and deformation of the mainshock are consistent with an intra-slab event within the subducting plate.  The event tested the region’s earthquake readiness more than any earthquake during the last 50 years (see summary by West et al., 2019). Resulting ground motions were highly variable, commonly 0.2-0.3 g, and landslides and liquefaction features were observed in a number of places (Jibson et al., 2019). The event emphasized the challenges in estimating the probabilistic hazard posed by intraslab earthquakes, which lacks surface faulting linked to coseismic displacements and hence the difficulty in identifying distinctive paleoseismic records for such events. Constraining the recurrence of such earthquakes is one of the most important parameters for seismic hazard assessments for southern Alaska. An important research topic along all active continental margins is aimed at understanding the minimum earthquake magnitude required to trigger slope failure in different subaqueous environments, determining the frequency and the area over which mass transport deposits are generated during a particular event, and using this information to determine the frequency of similar earthquakes through time.

This research opportunity is aimed at examining the sedimentary record of the 2018 Anchorage earthquake in lakes and fjords of southern Alaska to better understand linkages between seismic shaking from an intraslab event and subaqueous depositional records. Identifying the nature of and regional extent of sedimentary deposits triggered by the 2018 earthquake is a first step toward finding records of similar intra-slab earthquakes, which are the most commonly felt type of earthquakes in Alaska. Applicants are encouraged to develop a research proposal aimed at addressing the following questions: (1) What subaqueous environments are more/less prone to experience slope failures based on physical characteristics of the sedimentary system (physiography, sediment type/accumulation, earthquake recurrence, etc)? (2) Can the Anchorage earthquake provide constraints on the minimum earthquake magnitude, or quantitative ground shaking levels, needed to generate shaking-related deposits around southern Alaska? (3) Can instraslab events in the sedimentary record be distinguished from other types of earthquake generated mass transport and/or climatically induced depositional events? (4) What is the recurrence of intraslab earthquakes in the Anchorage region?

Recent work in southern Alaska shows that lake and fjord bottom sediments are faithful recorders of strong shaking during earthquakes (e.g., Lee et al., 2006; Haeussler et al., 2007; Ryan et al., 2010; Brothers et al., 2016, Praet et al., 2017; Kuehl et al., 2017; Van Daele et al., 2019). Perhaps most relevant to this research opportunity, an earthquake-induced deposit has been confirmed in Eklutna Lake near Anchorage (Van Daele et al., 2019), but the broader area in which these distinct deposits are expected has not been investigated. Therefore, this research opportunity emphasizes recent sediments in the vicinity of the 2018 earthquake and the lakes and fjords as the ideal places to explore for both earthquake‐triggered surficial sediment remobilization.

Using the 2018 earthquake as a calibration event, the identification and dating of such events in the lake and fjord sediment records can then be used to develop recurrence intervals and to infer the relative magnitude of shaking of past events. Taken together, this Mendenhall opportunity links several programs within the USGS Natural Hazards Mission Area, bridges many scientific disciplines and may guide future studies along other active U.S. margins (e.g., Cascadia, California, Caribbean). In summary, this research opportunity will be streamlined with ongoing efforts to (1) develop a suite of geophysical imaging/geological sampling approaches for lakes and fjords of southcentral Alaska, (2) plan and execute field-based projects that will inform the frequency and magnitude of similar earthquakes, and (3) set the foundation for similar studies across Alaska during the next decade(s) that are critical to developing accurate seismic hazard assessments.

The proposed Mendenhall opportunity will be integrated into larger regional efforts involving the USGS, Alaska Division of Geological and Geophysical Surveys, NOAA and academic partners (Ghent University). By working with a multi-disciplinary team to study the geologic and geophysical properties of southcentral Alaska, the Mendenhall Fellow will have an opportunity to interact with a broad, integrated research team spanning different USGS Centers and Mission Areas (Coastal and Marine Hazards and Resources Program and the Earthquake Hazards Program). By combining field studies with analytical expertise and facilities around the USGS, the postdoctoral fellow can develop a robust research project with diverse supervision/mentoring. 

Ideal candidates would have experience with: 1) sediment core collection and analyses using advanced laboratory techniques and 2) experience with interpretation of sediment proxy data, dating techniques (e.g., radiocarbon, lead isotope, etc), and (ideally) high-resolution seismic stratigraphy and paleoseismology.

Interested applicants are strongly encouraged to contact the Research Advisors early in the application process to discuss project ideas.

References:

Brothers, D. S., Haeussler, P. J., Liberty, L., Finlayson, D., Geist, E., Labay, K., & Byerly, M. (2016). A submarine landslide source for the devastating 1964 Chenega tsunami, southern Alaska. Earth and Planetary Science Letters, 438, 112–121.

Haeussler, P. J., Lee, H. J., Ryan, H. F., Labay, K., Kayen, R. E., Hampton, M. A., & Suleimani, E. (2007). Submarine slope failures near Seward, Alaska, during the M9. 2 1964 earthquake. In Submarine Mass Movements and their consequences(pp. 269–278). Springer.

Jibson, R.W., R. Grant, A.R., Witter, R.C., Allstadt, K.E., Thompson, E.M. and Bender, A.M., 2019. Ground Failure from the Anchorage, Alaska, Earthquake of 30 November 2018. Seismological Research Letters, https://doi.org/10.1785/0220190187.

Kuehl, S.A., Miller, E.J., Marshall, N.R., and Dellapenna, T.M., 2017, Recent paleoseismicity record in Prince William Sound, Alaska, USA: Geo-Marine Letters, v. 37, p. 527-536, doi: 10.1007/s00367-017-0505-7

Lee, H., Ryan, H., Kayen, R. E., Haeussler, P. J., Dortnell, P., & Hampton, M. A. (2006). Varieties of submarine failure morphologies of seismically-induced landslides in Alaskan fjords. Norsk Geologisk Tidsskrift, 86(3), 221.

Praet, N., Moernaut, J., Van Daele, M., Boes, E., Haeussler, P.J., Strupler, M., Schmidt, S., Loso, M.G., and De Batist, M., 2017, Paleoseismic potential of sublacustrine landslide records in a high-seismicity setting (south-central Alaska), Marine Geology, v. 384, p. 103-119, https://doi.org/10.1016/j.margeo.2016.05.004

Ryan, H. F., Lee, H. J., Haeussler, P. J., Alexander, C. R., & Kayen, R. E. (2010). Historic and paleo-submarine landslide deposits imaged beneath Port Valdez, Alaska: implications for tsunami generation in a glacial fiord. In Submarine Mass Movements and Their Consequences (pp. 411–421). Springer.

Van Daele, M., Haeussler, P.J., Witter, R., Praet, N., De Batist, M., 2019, The sedimentary record of the 2018 Anchorage Earthquake in Eklutna Lake, Alaska: Calibrating the lacustrine seismograph: Seismological Research Letters, https://doi.org/10.1785/0220190204. 

West, M.E., Bender, A., Gardine, M., Gardine, L., Gately, K., Haeussler, P., Hassan, W., Meyer, F., Richards, C., Ruppert, N. and Tape, C., 2019. The 30 November 2018 M w 7.1 Anchorage Earthquake. Seismological Research Letters, https://doi.org/10.1785/0220190176.

Proposed Duty Station: Santa Cruz, CA

Areas of PhD: geology, geophysics, oceanography, seismology 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: Research Geologist, Research Geophysicist, Research Oceanographer

(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: Audrey Tsujita, 916-278-9395, atsujita@usgs.gov