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Effects of Frictional Behavior and Geometry of Subduction Fault on Coseismic Seafloor Deformation

Pacific Geoscience Centre, Geological Survey of Canada, 9860 West Saanich Road, Sidney, British Columbia, Canada V8L 4B2 kwang{at}nrcan.gc.ca

The seismogenic zone of subduction faults appears to have an updip limit, seaward of which the fault exhibits velocity-strengthening behavior. We use a two-dimensional finite element model including a frictional subduction fault to explore how coseismic strengthening of the updip segment affects seafloor deformation. For a stress drop of a few MPa along the seismogenic zone, strengthening of the updip segment by a comparable amount can prevent the rupture from breaking the trench. The resultant seafloor uplift is much larger than that predicted by a model of equal seismic moment or maximum fault slip in which the seismogenic zone extends to the trench. With a curved-fault geometry, although a lower degree of coseismic strengthening of the updip segment leads to greater slip in the shallowest part of the fault, it produces smaller seafloor uplift, contrary to a popular belief. Given the paucity of direct observations of the coseismic behavior of the updip segment, the models yield important information for understanding rupture mechanics of subduction faults and tsunami generation. We also illustrate how the results may be used to guide fault slip parameterization in analytical dislocation models.