← Back to Sessions

Detailed Marine Paleoseismic Records From Earthquake Triggered Submarine Landslides in Outer Prince William Sound, Alaska

Description: 

The USGS is engaged in a multi-year effort to investigate the earthquake, landslide and tsunami hazards along the Alaska-Aleutian Subduction Zone. As part of this work, high-resolution chirp subbottom and sparker seismic reflection profiles were collected across Prince William Sound (PWS) in 2024 and 2025. PWS, which lies atop the Alaska-Aleutian megathrust boundary, has extremely high sedimentation rates that offer detailed marine paleoseismic records of both megathrust and smaller regional earthquakes.

Sediment in the central sound is primarily sourced from glacial retreat and the Copper River delta, whose sediment plume is swept northward along the coast and funneled into southern PWS at Middle Ground Shoal (MGS) in Orca Bay. MGS is an ~100m thick prodelta with extensive mass wasting visible in both the seafloor bathymetry and subbottom data. Slope failures are also pervasive along the steep walls of the central PWS channel. The headwalls and debris fans of these failures are evident in the bathymetry data and imaged as multiple, stacked mass transport deposits (MTDs) in the subbottom data. These chaotic, blocky MTDs grade into highly reflective deposits interpreted as sand-rich graded beds in the basin centers. With an epicenter in northeastern PWS, the 1964 M9 Great Alaska earthquake appears to have triggered widespread slope failures with stratigraphically synchronous deposits across the central basin and Orca Bay. The 1964 deposit is a 4-8m thick MTD that thins basinward into a series of stacked graded beds. Beneath this, we observed at least 10 basin-wide, MTD-graded bed events within the late Holocene (<~4.5kyr), consistent with previous megathrust recurrence estimates. The largest and most widespread deposit appears to be the penultimate event, which has a ponded MTD >30m thick in the deeper parts of the basin. Many of the ponded deposits are also overlain by a series of stacked graded beds indicative of failures from multiple sides of the basin. Numerous additional, thinner graded beds between these megathrust event deposits may record more frequent, smaller intraslab or crustal earthquakes.

Session: Subaqueous Evidence for Earthquakes, Coseismic Landslides, Tsunamis and other Cascading Hazards [Poster]

Type: Poster

Date: 4/15/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Jenna C. Hill

Student Presenter: No

Invited Presentation: 

Poster Number: 160

Authors