STRESS AND THE SPATIAL-DISTRIBUTION OF SEISMICITY IN THE CENTRAL ALEUTIANS

Changes in static stress caused by 52 earthquakes of average m(b) 4.7 are modeled and compared to changes in the spatial distribution of mostly smaller surrounding earthquakes recorded by the Central Aleutian Seisimic Network. The comparisons have been used to evaluate possible fault failure criteria and background stress states appropriate for a subduction zone. Statistical measures were developed to assess the significance of changes in spatial distribution of seismicity. The significance of changes in the spatial distribution of seismicity occurring near the times of target earthquakes was evaluated by comparing their to changes occurring at other times in the same catalog. The, most successful model includes background stresses caused by viscous drag forces exerted on the subducting plate as it moves through the mantle and assumes that surrounding seismicity occurs on strong faults in all orientations. This stress state suggests that, the main thrust zone between the subducting and overriding plates is weak, because otherwise forces from the collision of the two plates would dominate the stress field. The best-fitting model is preferred over three other combinations of background stress state and fault friction which fit the data equally well because it more strongly correlates with seismicity near the larger earthquakes in more active areas.