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 mos tly smaller surrounding earthquakes recorded by the Central Aleutian S eisimic Network. The comparisons have been used to evaluate possible f ault failure criteria and background stress states appropriate for a s ubduction zone. Statistical measures were developed to assess the sign ificance of changes in spatial distribution of seismicity. The signifi cance of changes in the spatial distribution of seismicity occurring n ear the times of target earthquakes was evaluated by comparing their t o changes occurring at other times in the same catalog. The, most succ essful model includes background stresses caused by viscous drag force s exerted on the subducting plate as it moves through the mantle and a ssumes that surrounding seismicity occurs on strong faults in all orie ntations. This stress state suggests that, the main thrust zone betwee n the subducting and overriding plates is weak, because otherwise forc es from the collision of the two plates would dominate the stress fiel d. The best-fitting model is preferred over three other combinations o f background stress state and fault friction which fit the data equall y well because it more strongly correlates with seismicity near the la rger earthquakes in more active areas.