Landslides and Megathrust Splay Faults Captured by the Late Holocene Sediment Record of Eastern Prince William Sound, Alaska

Authors

Shaun P. Finn, Boise State University
Lee M. Liberty, Boise State UniversityFollow
Peter J. Haeussler, U.S. Geological Survey
Thomas L. Pratt, U.S. Geological Survey

Document Type

Article

Publication Date

10-2015

Abstract

We present new marine seismic‐reflection profiles and bathymetric maps to characterize Holocene depositional patterns, submarine landslides, and active faults beneath eastern and central Prince William Sound (PWS), Alaska, which is the eastern rupture patch of the 1964 M_w 9.2 earthquake. We show evidence that submarine landslides, many of which are likely earthquake triggered, repeatedly released along the southern margin of Orca Bay in eastern PWS. We document motion on reverse faults during the 1964 Great Alaska earthquake and estimate late Holocene slip rates for these growth faults, which splay from the subduction zone megathrust. Regional bathymetric lineations help define the faults that extend 40–70 km in length, some of which show slip rates as great as 3.75  mm/yr. We infer that faults mapped below eastern PWS connect to faults mapped beneath central PWS and possibly onto the Alaska mainland via an en echelon style of faulting. Moderate (M_w >4) upper‐plate earthquakes since 1964 give rise to the possibility that these faults may rupture independently to potentially generate M_w 7–8 earthquakes, and that these earthquakes could damage local infrastructure from ground shaking. Submarine landslides, regardless of the source of initiation, could generate local tsunamis to produce large run‐ups along nearby shorelines. In a more general sense, the PWS area shows that faults that splay from the underlying plate boundary present proximal, perhaps independent seismic sources within the accretionary prism, creating a broad zone of potential surface rupture that can extend inland 150 km or more from subduction zone trenches.

Copyright Statement

Finn, Shaun, Liberty, Lee, Heussler, Peter, and Pratt, Thomas. Landslides and Megathrust Splay Faults Captured by the Late Holocene Sediment Record of Eastern Prince William Sound, Alaska. Bulletin of the Seismological Society of America, 105, pp. 2343-2353, 2015, © Seismological Society of America.

Publication Information

Finn, Shaun P.; Liberty, Lee M.; Haeussler, Peter J.; and Pratt, Thomas L.. (2015). "Landslides and Megathrust Splay Faults Captured by the Late Holocene Sediment Record of Eastern Prince William Sound, Alaska". Bulletin of the Seismological Society of America, 105(5), 2343 - 2353. https://doi.org/10.1785/0120140273