Seismo-Thermo-Mechanical Modeling of Subduction Zone Seismicity: Methodology, Applications, and Perspectives

Abstract:

Recent megathrust earthquakes illustrated both their disastrous human and economic impact and our limited physical understanding of their spatial and temporal occurrence. To improve long-term seismic hazard assessment by overcoming the restricted direct observations in both time and space, we developed the new numerical seismo-thermo-mechanical (STM) model presented here.

This 2D continuum-mechanics based, viscoelastoplastic model uses an Eulerian-Lagrangian finite difference framework with similar on- and off-fault physics. This typically long-term geodynamic approach is extended to study short-term seismogenesis through a local invariant implementation of strongly slip rate-dependent friction. This approach may help to shed light onto the interaction between long-term subduction dynamics and deformation and associated short-term seismicity. Additional advantages of this STM approach include the physically consistent emergence of rupture paths, both on- and off-megathrust, and the inclusion of three key ingredients for seismic cycling --rate-dependent friction, slow tectonic loading, and visco-elastic relaxation--.

The validation of this approach is accomplished through a comparison with an analogue seismic cycle model (van Dinther et al., JGR, 2013a). The applicability, potential, and limitations were further illustrated in a more realistic geometry and physical setup of the Southern Chilean margin (van Dinther et al., JGR, 2013b). Extending these rapid transient slip cycles over time-scales of tens of thousands of years showed that ~5% of cyclic deformation is not recovered and is instead stored as permanent, anelastic deformation within the wedge. Analyzing off-megathrust events specifically showed they influence the megathrust cycle distinctly, while, especially steeply dipping outerrise events, also also increase the tsunami hazard significantly (van Dinther et al., GRL, 2014).

The innovative character of this seismo-thermo-mechanical approach opens a world of interdisciplinary research between geodynamics and seismology. To illustrate this approaches perspectives we will give examples illustrating the role of downdip seismogenic zone width for super cycles and the role of a weak viscous lower crust for surface displacements and a secondary zone of uplift.