DEPENDENCE OF EARTHQUAKE SIZE DISTRIBUTIONS ON CONVERGENCE-RATES AT SUBDUCTION ZONES

The correlation of numbers of thrust earthquakes of moment magnitude 7 or greater in this century at subduction zones with convergence rate results from a combination of lower recurrence intervals for earthquak es of a given size where slip rates are high and a peak in the global distribution of subduction zone convergence rates at high values (55 t o 90 mm/yr). Hence, physical mechanisms related to convergence rate, s uch as plate interface force, slab pull, or thermal effects, are not r equired to explain the distribution of large earthquakes with converge nce rate. The seismic coupling coefficient ranges from 10% to 100% at subduction zone segments where convergence is faster than 45 mm/yr but does not correlate with rate. The coefficient is generally orders of magnitude lower at rates below 40 mm/yr which may be due to long recur rence intervals and a short sampling period (94 years).