Hirakawa1,2 and Shuo Ma1

1. Department of Geological Sciences, San Diego State University
2. IGPP, Scripps Insitute of Oceanography, University of California, San Diego

Strain Localization in the Coulomb Wedge and the Stabilizing Role of Fluids: A New Splay Faulting Model in the Shallow Subduction Zone

Coseismic slip on splay faults has been widely recognized in conjunction with several large earthquakes in the shallow subduction zone (e.g., the 1964 Alaska earthquake). Large amounts of seafloor uplift due to the steep dips of these faults coupled with shorter tsunami travel times allowed by the landward location of the splay faults relative to the trench leads to the possibility of catastrophic tsunamis. Here we propose a new framework for understanding splay faulting in subduction zones based on the Coulomb wedge theory (Dahlen, 1990; Wang and Hu, 2006), which assumes that the material in the wedge is on the verge of failure everywhere and has been used to explain several long-lasting mysteries associated with shallow subduction earthquakes (Ma, 2012; Ma and Hirakawa, 2013). Our new model comprises a shallow dipping thrust fault and has no preexisting splays. By incorporating undrained inelastic off-fault response into a dynamic rupture model, we show that splay faults materialize in the form of inelastic strain localization, and the ability to generate them has a strong dependence on dynamic pore pressure variations. Specifically, we demonstrate that the potential to generate splay faults is mainly influenced by the Skempton’s coecient. For relatively large Skempton’s coecients off-fault failure is broadly distributed throughout the wedge (Ma, 2012; Ma and Hirakawa, 2013). However the inelastic strain localizes for low Skempton’s coefficients, and splay faults are formed, which significantly affects seafloor uplift. We also show that splay fault rupture strongly influences the rupture on the main fault, and in some cases it is able to halt the main fault’s rupture. This new framework of splay fault development unifies our understanding of different faulting characteristics in shallow subduction zones and tsunamigenesis.

2013 SCEC Annual Meeting