Upper plate stressing and seismicity in the subduction earthquake cycle

We investigate upper plate stressing during the earthquake cycle in a subduction segment, using three-dimensional (3-D) elastic models to address the effects of strongly heterogeneous coupling along strike of the interplate interface. We show how heterogeneity controls the locations and mechanisms of seismicity in the upper plate. Oblique subduction segments, two from the Aleutians (Andreanof Islands 1986 and Rat Islands 1965) and one from Indonesia (Biak 1996) are studied. All examples of upper plate seismicity from the Aleutians represent events occurring toward the beginning of a new cycle, while in B iak, Indonesia, the examined events occur both toward the end of one cycle and the beginning of the next. In the majority of cases studied, the location and mode of the upper plate seismicity are consistent with spaceand time-dependent stressing as predicted by modeling. This confirms earlier observations that seismicity in the vicinity of large/great subduction earthquakes (toward the outer rise, at intermediate depth, and now in the upper plate) depends, in an interpretable manner, on the stage in the earthquake cycle as well as on distribution of coupling along the interplate interface.