Collaborative Research: Imaging the Locked-to-Slipping Transition for the 1964 Alaska Earthquake Rupture Zone

The largest recorded earthquake in United States history, a magnitude 9.2 event in 1964, occurred at the Alaska subduction zone. Some sections of this earthquake rupture zone are currently locked and accumulating strain, while other sections are creeping. This project will image the plate interface across this region to help determine the causes for the changes in slip behavior. The results will improve understanding of the processes that generate great earthquakes, with relevance to earthquake hazards in Alaska and other subduction zones worldwide. The project will provide at-sea training for several graduate students from multiple institutions. This study will acquire long-offset multi-channel seismic reflection and wide-angle ocean bottom seismometer data spanning the entire rupture zone of the 1964 earthquake. Profiles will image the incoming plate structure, upper plate fault geometries, megathrust reflection signature, and material properties near the trench within and across the 1964 rupture zone. Key hypotheses that the dataset will be able to test are: 1) Along-strike variability in plate boundary slip mechanisms during great earthquakes reflects variability in subduction inputs. 2) The character and location of the Yakutat/Pacific boundary controls variations in locking and coseismic slip. 3) Major forearc structures that experience co-seismic slip are rooted in the megathrust and influenced by variations in plate interface geometry and properties. 4) Areas of near-trench rupture and tsunamigenesis occur in regions where relatively rigid forearc crust is closer to the trench and/or pore-fluid pressures are largely absent on the shallow plate boundary. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.