Coseismic Strengthening of the Shallow Subduction Megathrust Further Enhances Inelastic Wedge Failure and Efficiency of Tsunami Generation

Evan T. Hirakawa, & Shuo Ma

Published August 15, 2016, SCEC Contribution #6770, 2016 SCEC Annual Meeting Poster #069

The shallow portion (upper 5 – 10 km) of the subduction megathrust fault, governed by velocity-strengthening friction, has generally been considered to reduce near-trench slip and tsunamigenesis. However, Kozdon and Dunham (2013) showed that large shallow slip can still occur in the presence of velocity-strengthening friction if the rupture is driven strongly from the deeper fault segment (e.g., the 2011 Tohoku earthquake). Here we extend this dynamic rupture model to include inelastic wedge failure (Seno, 2000; Tanioka and Seno, 2001; Ma, 2012; Ma and Hirakawa, 2013). We show that increased basal friction due to velocity strengthening can further drive the outer wedge into failure, which was first proposed by Wang and Hu (2006). Inelastic wedge failure reduces slip on the fault, but at the same time increases the efficiency of generating seafloor uplift (the uplift efficiency is defined as the ratio of the volume of uplift to seismic potency, which is dimensionless), especially when the fault is shallowly dipping. As the transition of friction from velocity weakening to velocity strengthening is more abrupt strain can localize in the outer wedge developing mega-splay faults. This model can explain a range of different mechanisms for tsunamigenesis: large near-trench slip, splay faulting, and distributed inelastic wedge failure. The occurrence of each is controlled by the wedge strength and fault friction properties.

Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-700239.

Citation
Hirakawa, E. T., & Ma, S. (2016, 08). Coseismic Strengthening of the Shallow Subduction Megathrust Further Enhances Inelastic Wedge Failure and Efficiency of Tsunami Generation. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)