Numerical Modeling of Dynamically Triggered Shallow Slow Slip Events in New Zealand by the 2016 Mw 7.8 Kaikoura Earthquake

The 2016 M-w 7.8 Kaikoura earthquake triggered widespread slow slip events (SSEs) in the northern Hikurangi subduction zone, providing a unique opportunity to study the mechanism of dynamic triggering of SSEs. Here we simulate SSEs near Gisborne, New Zealand, in the framework of rate-and-state friction. Low effective normal stress (similar to 0.4MPa) on the shallow subduction interface is needed to reproduce the observed repeating, spontaneous SSEs. Dynamic stress perturbations from the Kaikoura mainshock are adequate to trigger SSEs with characteristics similar to observation. SSE propensity to dynamic triggering mainly depends on the timing of perturbation with respect to the SSE cycle and the maximum Coulomb stress change. Once the perturbation amplitude exceeds an initial threshold, prolonged stress perturbations tend to decrease the triggering threshold hence promote dynamic triggering of SSEs. Therefore, shallow SSEs are more likely to be dynamically triggered than their deep counterparts because of enhanced stress perturbation (magnitude and duration) from the sedimentary wedge. Plain Language Summary Slow slip events, gradual fault movement lasting days to months, have been documented in subduction zones worldwide. Occasionally, distant earthquakes can trigger these events, but how the triggering happens is still not well understood. Recently, widespread slow slip events have been recorded in the northern Hikurangi subduction zone and are believed to be triggered by the 2016 Kaikoura earthquake in New Zealand. In this study, we develop a computer model for regular, repeating slow slip events in northern Hikurangi and analyze if applying the Kaikoura earthquake waves to the model leads to the triggering of slow slip events. We find that our model can reproduce the observed slow slip events in northern Hikurangi following the Kaikoura earthquake. Our model explains a potential underlying mechanism for the triggering process of slow slip events. Our results further provide insights into how, where, and when slow slip events in subduction zones are triggered by earthquake waves in general.