Linking geodynamic simulations of seamount subduction to seismic cycle modeling

Seamounts are ubiquitous features of oceanic plates and are commonly subducted at convergent margins, where they can significantly deform the overriding plate. Numerous studies have proposed that subducting seamounts can influence megathrust slip behavior, either by promoting aseismic creep or acting as persistent barriers to earthquake rupture propagation. However, the interplay between long-term structural evolution and short-term seismicity remains poorly understood.

To investigate this relationship, we couple the long-term geodynamic code pTatin2d with the seismic cycle code Tandem. We first perform long-term geodynamic simulations with pTatin2d, focusing on the effects of subducting multiple seamounts. These simulations allow us to track the evolution of fault geometries, stress fields, and structural complexities in the upper plate over millions of years. At selected stages of seamount subduction, we extract the geometry of faults and the associated stress distribution to initialize seismic cycle simulations with Tandem.

To elucidate the role of each extracted parameter, and thereby develop a methodology linking geodynamic simulations to seismic cycle models, we systematically and independently investigate the effects of normal stress heterogeneity, topography, basal fault geometry, and upper-plate faulting on the seismic cycle. Specifically, we observe that variations in normal stress can act both as barriers to earthquake propagation and as asperities where earthquakes can nucleate. The upper plate faults also play an important role. Our simulations show that multiple splay faults can be activated during a single megathrust event. Rupture can also nucleate on a splay fault and subsequently propagate onto the main fault.

We then consider the combined influence of all extracted parameters, allowing us to assess how inherited structural and stress conditions control earthquake recurrence, magnitude, and the spatial distribution of seismic events. Our results provide new insights into how bathymetric highs modulate seismic behavior in subduction zones, bridging long-term geodynamics and short-term seismic processes.