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 heterogeneity in terms of intermediate-depth seismicity (∼70-300 km), orientations of slab stress, and volcanism. We compile the intermediate-depth earthquakes of South America from the Harvard Centroid Moment Tensor (CMT) catalogue to determine along-strike dip variations, and we explore the variable level of correlation between these observations. Primary results are three-fold: (1) Consistency among orientation of tension axes, highest level seismicity, and occurrence of volcanism is associated with steeply-dipping regions (20°-30°). (2) Volcanism and intermediate-depth seismicity exhibit no direct correlation, suggesting that earthquake faulting is not a necessary condition for transport of dehydrated fluids out to the mantle wedge for initiation of melting. (3) Comparison of slab thermal structures between regions with and without volcanism suggests that for certain wedge widths, the maximum temperature in the mantle wedge is higher for the former than for the latter.