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Variations in Mass Transport Deposits That Record Strong Ground Motion Events in Western Prince William Sound, Alaska

Description: 

The fjords of Prince William Sound (PWS) overlie the westernmost Alaska-Aleutian subduction zone, including the epicentral region of the 1964 M_w 9.2 Great Alaska Earthquake. In 1964, intense shaking generated widespread destabilization and failure of submerged fjord sediments, which in turn generated devastating tsunamis that impacted several coastal communities in PWS. While sediments in some fjords failed catastrophically in 1964, others did not, suggesting that a complex interplay between basin physiography, sediment accumulation, and shaking intensity determines the degree of instability that develops within each local fjord depositional system. In summer 2020, the USGS collected a suite of nested multi-channel seismic and high-resolution Chirp data in several fjords of western Prince William Sound, as well as short-barrel, percussion-driven gravity cores to characterize the top ~2 m of sediment.

The effect of the 1964 earthquake has previously been identified in several of the surveyed basins (e.g., Passage Canal and Dangerous Passage) as a 5-10+ m thick deposit. Deposits with similar character and stratigraphic position, but with variable thickness (~0.3m to 15m) are observed in every basin surveyed, and we interpret these deposits to result from sediment remobilization in 1964. The ubiquity of the 1964 deposit imaged in chirp and MCS data implies that ground motions were sufficient to remobilize detectable levels of sediment. The variability in deposit character, however, suggests that variations in sediment supply precondition certain basins for larger failures than others. Using the 1964 deposits as a template, we investigate the potential relationship between pre-conditioning factors and strong ground motion in remobilizing sediment and extend this investigation past the historical period to previous strong ground motion events. The results of this study may have important implications for quantifying the relationships between seismic parameters (i.e., shaking intensity), and the sedimentary response (i.e., total volume remobilized and thickness of the resulting deposit).

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments - I

Type: Oral

Date: 5/1/2024

Presentation Time: 08:30 AM (local time)

Presenting Author: Drake

Student Presenter: No

Invited Presentation: 

Authors