科研之友
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摘要
We model plate boundary slip at the outer (oceanward) segment of the megathrust wedge as slip at the base of a two-dimensional elastic wedge, subject to gravity force, with a sloping seafloor at the top, and drag at the bottom from a rigid plate in frictional contact. The stress and displacement fields in the wedge are given analytically as functions of basal frictional coefficient mu(e). Unlike either conventional dislocation models (constant slip) or crack models (constant stress drop), our wedge model (constant mu(e) drop) does not show a stress singularity at the updip toe of the plate boundary. The slip increases, but the stress drop decreases updip along the fault toward the trench axis. There is a minimum stress difference state in the wedge when mu(e) is varied. By referring to this state (mu(e) = mu(ec)), the stress state is separated into a horizontally tensile regime (mu(e)< mu(ec)) and a horizontally compressional regime (mu(e) > mu(ec)). Slip associated with a mu(e) drop in the range mu(e) <= mu(ec) occurs toward increasing horizontal tension and shear energy. Such earthquakes include tsunami earthquakes occurring in the outer segment and the 2011 great Tohoku-Oki earthquake, which involved both the outer and inner segments, with much larger slip in the outer segment. These earthquakes are characterized by an almost complete drop of basal stress, which brings the wedge into the maximum tensile state, leading to the rare occurrence of thrust aftershocks at the base of the wedge and frequent occurrence of normal fault aftershocks within the wedge.
- 出版日期2014-5
