Regional and stress drop effects on aftershock productivity of large megathrust earthquakes

Abstract

AbstractThe total number of aftershocks increases with main shock magnitude, resulting in an overall well‐defined relationship. Observed variations from this trend prompt questions regarding influences of regional environment and individual main shock rupture characteristics. We investigate how aftershock productivity varies regionally and with main shock source parameters for large (Mw ≥ 7.0) circum‐Pacific megathrust earthquakes within the past 25 years, drawing on extant finite‐fault rupture models. Aftershock productivity is found to be higher for subduction zones of the western circum‐Pacific than for subduction zones in the eastern circum‐Pacific. This appears to be a manifestation of differences in faulting susceptibility between island arcs and continental arcs. Surprisingly, events with relatively large static stress drop tend to produce fewer aftershocks than comparable magnitude events with lower stress drop; however, for events with similar coseismic rupture area, aftershock productivity increases with stress drop and radiated energy, indicating a significant impact of source rupture process on productivity.