Linear and Nonlinear Relations between Relative Plate Velocity and Seismicity

Relationships between relative plate velocity and seismicity differ by plate-boundary class. We test the null hypothesis of linearity of earthquake rates with velocity in each of seven classes. A linear relationship is expected if earthquake rate is proportional to seismic moment rate, which is proportional to relative plate velocity. To reduce bias by aftershocks and swarms, we estimate independence probabilities of earthquakes and use them as weights. We assign shallow earthquakes to boundary steps and classes, then sort boundary steps within each class by velocity and plot cumulative earthquakes against cumulative model moment rate. We use two measures of nonlinearity and 10(4) stochastic simulations to assess significance. In subduction zones the relationship between seismicity and velocity is nonlinear with 99.9% confidence. Slower subduction at