Synthetic seismicity models for the Wellington Region, New Zealand: Implications for the temporal distribution of large events

Our previous synthetic seismicity model for multiple interacting faults in a three-dimensional half-space has been extended and applied to the Wellington region, New Zealand, generating long catalogs of earthquakes for studying the effects of elastic interactions on the temporal distribution of large events. The region is one of oblique plate convergence with the interface between the subducting and overlaying plates at an average depth of 22 km. Faults included, besides the subduction thrust, are segments of the four major arc-parallel, strike-slip faults overlying the plate interface. We have used 40 different models, with geometric and mechanical parameters chosen at random within reasonable ranges, to generate catalogs of 200,000 years duration each. For comparison, each model was rerun with the elastic interaction suppressed. Considering events of magnitude 7.2 or more (''characteristic'' events in the sense that they rupture most of a fault plane), the number of short (<10 years) interevent times is higher than for the corresponding case with no interactions, for all models but one: the ratio ranges from 0.94 to 37.21 (9.46 average). For longer interevent times (10 to 250 years) the relative numbers are in the opposite sense. For still longer interevent times (>250 years), the relative numbers are again mostly higher. Experiments with simple models indicate that this pattern requires both interfault enhancement and inhibition of large events. Mutual enhancement occurs most often between the subduction thrust and the overlying strike-slip faults and between the two segments of the Wellington fault that almost join end to end. Mutual inhibition mostly occurs between the subparallel strike-slip faults.