Link between plate fabric, hydration and subduction zone seismicity in Alaska

Subduction zones worldwide exhibit remarkable variation in seismic activity over short distances of about tens of kilometres along their length. The properties of the subducting oceanic plate are believed to influence this seismic behaviour. However, comparisons between seismicity and plate attributes such as thermal structure made over large scales of hundreds of kilometres typically yield poor correlations. Here we present results from controlled-source seismic data collected offshore of the Alaska Peninsula. We find that fabric in the subducting oceanic plate-the orientation and style of remnant faults originally created at the mid-ocean ridge-can contribute to abrupt changes in faulting and hydration of the plate during bending before subduction. Variations in fabric, bending faulting and hydration correlate with changes in seismicity throughout the subduction zone. More interplate and intermediate-depth intraplate earthquakes are observed where the pre-existing fabric is aligned with the trench and there is more bend faulting and hydration. This suggests that pre-existing structures in the subducting plate are an important control on abrupt variations in deformation and plate hydration and on globally observed short-wavelength variations in seismicity at subduction zones.