INFLUENCES OF RECURRENCE TIMES AND FAULT ZONE TEMPERATURES ON THE AGE-RATE DEPENDENCE OF SUBDUCTION ZONE SEISMICITY

Correlations among subduction zone seismicity, convergence rate and su bducting plate age are reassessed considering the possible roles of bo th recurrence times and fault zone temperatures. Distributions of eart hquakes with respect to subducting lithosphere age and convergence rat e are grossly explained by a recurrence relation when ages and rates a t the world's trenches are taken into account. Correlations between ma ximum earthquake size M-W(max) and convergence rate occur because fast er subduction lowers the average recurrence time, so that at random wi thin a limited sampling time, faster subduction zones have larger eart hquakes. Published empirical slopes of an assumed linear relationship between M-W(max) and convergence rate are predicted to within 1 standa rd deviation by such a recurrence model. Recurrence predicts that M-W( max) should be related to the logarithm of convergence rate and revise d age-rate-M-W(max) data agree with such a relationship. No resolvable global correlation between age and M-W(max) is found. Hence mechanica l explanations of subduction zone seismicity based on such correlation s are not required. Predicted average steady state temperatures, based on age and dip of the subducting lithosphere and convergence rate, at most subduction zone thrust faults are within a small range of values (+/-50 degrees C). The few warm outliers, that is, Cascadia, Mexico, and southernmost Chile (south of Chile Rise) that subduct very young l ithosphere, also have low seismic coupling coefficients suggesting tha t high temperature may inhibit seismicity. Fault zone temperatures can explain global variations in seismic coupling coefficients as well as the slab anchor model of Scholz and Campos [1995]. Applying this to t he Cascadia subduction zone, in contrast to conclusions drawn from mec hanical models of subduction and consistent with many other observatio ns, due to its extremely high temperature, Cascadia may be a region wh ere aseismic subduction predominates.