Spatial Variation of Slip Behavior Beneath the Alaska Peninsula Along Alaska‐Aleutian Subduction Zone

We resurveyed preexisting campaign Global Positioning System (GPS) sites and estimated a highly precise GPS velocity field for the Alaska Peninsula. We use the TDEFNODE software to model the slip deficit distribution using the new GPS velocities. We find systematic misfits to the vertical velocities from the optimal model that fits the horizontal velocities well, which cannot be explained by altering the slip distribution, so we use only the horizontal velocities in the study. Locations of three boundaries that mark significant along‐strike change in the locking distribution are identified. The Kodiak segment is strongly locked, the Semidi segment is intermediate, the Shumagin segment is weakly locked, and the Sanak segment is dominantly creeping. We suggest that a change in preexisting plate fabric orientation on the downgoing plate has an important control on the along‐strike variation in the megathrust locking distribution and subduction seismicity. Plain Language Summary Understanding controls on slip behavior is a key objective of scientists from many different disciplines across solid earth sciences. Measuring the spatial changes in slip on the subduction plate interface can improve our understanding of factors that govern the size, location, and frequency of great destructive earthquakes. Does slip change abruptly or gradually along the length of the subduction zone? We estimate a new model that represents more precisely changes in slip on the interface between North American plate and Pacific plate beneath the Alaska Peninsula. We show that these changes in slip are abrupt and the locations of the changes correlate with features on the downgoing oceanic plate. The orientation of preexisting weakness on the Pacific plate correlates with the estimated slip variations and changes in the seismicity. In the areas that dominantly creep, the Pacific plate has been faulted extensively as it was bent going over the outer rise, leading to a rougher fault surface and more water being brought down with the subducted plate. In the areas that are mostly locked by friction, the faults in the Pacific plate are oriented nearly perpendicular to the trench and there is minimal faulting at the outer rise. Key Points The width of the locked region decreases stepwise from NE to SW along strike Three sharp boundaries that mark changes in fault coupling are identified The change in preexisting fabric orientation contributes significantly to the change in fault locking and