THE 1964 GREAT ALASKA EARTHQUAKE AND THE SUBDUCTION ZONE EARTHQUAKE CYCLE

Back in the 1960s, the realization that the 1964 Great Alaska earthquake occurred on a low angle thrust fault helped to confirm the basic theory of plate tectonics. But the earthquake has contributed to our understanding of the subduction zone earthquake cycle in a number of other ways. Rapid postseismic uplift in the decade following the earthquake provided incontrovertible evidence for postseismic deformation. Later geodetic studies of the 1964 earthquake rupture zone demonstrated that these postseismic transients can be exceptionally long-lived, and have provided important insights into the persistence of seismic asperities at subduction zones.

This talk focuses on the evolution of slip on the megathrust over time. The coseismic slip distribution was strongly heterogeneous, with very large slip in 2 (or perhaps 3) distinct patches. The earthquake was then followed by rapid afterslip, mainly on the deeper part of the Megathrust, and the coseismic stress changes also caused flow in the viscoelastic mantle wedge; that flow continues decades after the earthquake although the afterslip probably does not. Over the last two decades, we have observed that the first order pattern of locked patches on the shallow megathrust matches the coseismic slip pattern, although the pattern of slip is not time-invariant. The region of the 1964 rupture produces very large slow slip events (slow earthquakes), and demonstrates that the downdip end of locked patches on the megathrust are subject to dynamic changes.