Variations in slab dip along the subducting Nazca Plate, as related to stress patterns and moment release of intermediate-depth seismicity and to surface volcanism

The subducting Nazca Plate shows a high degree of along-strike heterogeneit y in terms of intermediate- depth seismicity (similar to 70- 300 km), orien tations of slab stress, and volcanism. We compile the intermediate- depth e arthquakes of South America from the Harvard Centroid Moment Tensor (CMT) c atalogue to determine along- strike dip variations, and we explore the vari able level of correlation between these observations. Primary results are t hree- fold: (1) Consistency among orientation of tension axes, highest leve l seismicity, and occurrence of volcanism is associated with steeply- dippi ng regions (20 degrees- 30 degrees). (2) Volcanism and intermediate- depth seismicity exhibit no direct correlation, suggesting that earthquake faulti ng is not a necessary condition for transport of dehydrated fluids out to t he mantle wedge for initiation of melting. (3) Comparison of slab thermal s tructures between regions with and without volcanism suggests that for cert ain wedge widths, the maximum temperature in the mantle wedge is higher for the former than for the latter.