Comparison of seismic moment release rates along different types of plate boundaries

This is a global survey of seismic moment release rates (scalar moment/length/time) along five categories of plate boundaries; for shallow earthquakes we evaluate divergent, transcurrent and convergent boundaries; for deep earthquakes we consider separately boundaries where the deepest seismicity is intermediate (< 300 km) or deep-focus (500-600 km). The objective is to evaluate the typical range of rates observed and present the results in a form where it is straightforward to compare factors that affect rates in the different environments. For earthquakes occurring 1977-2005, the data are scalar moments from the global centroid moment tensor catalogue; for earthquakes 1900-1976, we use a standard formula to obtain moment from magnitudes in the Engdahl-Villasenor Centennial catalogue. Moment release rates correlate with relative velocity between plates along divergent and transcurrent boundaries; focal depth influences moment release rates along intermediate and deep-focus boundaries. After accounting for these effects and adjusting rates for the influence of the short (29-106 yr) data record, within each category the typical observed variation is about an order of magnitude. We estimate seismic coupling coefficients, that is, the proportions of plate tectonic slip accommodated as earthquake rupture and reflected in the moment rates. Coupling may be 0.7 or greater along shallow convergent boundaries where at least one plate is continental. For all other boundary categories coupling is generally less than 0.4; it is 0.2 or less along most divergent boundaries and for intermediate and deep boundaries at depths exceeding 100 km. These results confirm that there are fundamental mechanical differences in the failure processes acting along different categories of plate boundaries. One implication is that only along a few highly coupled boundaries is it plausible that analysis of seismicity alone might lead to successful algorithms to predict large earthquakes.