Earthquake processes along the eastern Aleutian subduction zone do not behave the same way along its length. The properties of past megathrust earthquakes, modern seismicity, coupling, and tremor all vary along-strike. So why does the fault behave so differently from place to place?

To learn what controls a fault, it helps to change one thing while keeping the rest fixed. While subduction zones rarely perfectly cooperate, the eastern Aleutians offers an opportunity to largely isolate the role of the overriding plate. The incoming Pacific plate appears remarkably uniform along this margin, while the overriding plate changes from continental crust in the east of our study area to oceanic crust in the west. 

The area contains along-strike variability in seismicity, coupling, and tectonic tremor. It also spans the partial rupture patches of two significant and contrasting mid-20th century megathrust earthquakes. In 1946, a rupture near Unimak became one of the archetypal "tsunami earthquakes," generating a tsunami across the Pacific far out of proportion to its shaking. Just over a decade later, the 1957 Andreanof Islands earthquake ruptured a long segment to the west. 

Our study will place these consequential earthquakes in the context of the structure we image and the seismicity and tremor we catalog, to better understand what conditions produced them. We aim to test if the contrast between overriding continental and oceanic crust is the primary control on how megathrust earthquakes, tremor, coupling, and seismicity vary along the eastern Aleutians. Our results will improve understanding of megathrust behavior globally, including at ocean–ocean subduction settings that have long been understudied.