摘要：We investigated the effects of elastic heterogeneity on coseismic deformation associated with the 2011 Tohoku-oki
earthquake, Japan, using a 3-D finite element model, incorporating the geometry of regional plate boundaries. Using
a forward approach, we computed displacement fields for different elastic models with a given slip distribution. Three
main structural models are considered to separate the effects of different kinds of heterogeneity: a homogeneous
model, a two-layered model with crust–mantle stratification, and a crust–mantle layered model with a strong subducting slab. We observed two counteracting effects: (1) On large spatial scales, elastic layering with increasing rigidity with depth leads to a decrease in surface displacement. (2) An increase in rigidity from above the slab interface
to below causes an increase in surface displacement, because the weaker hanging wall deforms to accommodate
coseismic slip. Results for slip inversions associated with the Tohoku-oki earthquake show that slip patterns are modified when comparing homogeneous and heterogeneous models. However, the maximum slip only changes slightly:
It increases from 38.5 m in the homogeneous to 39.6 m in the layered case and decreases to 37.3 m when slabs are
introduced. Potency, i.e., the product of slip and fault area, changes accordingly. Layering leads to inferred slip distributions that are broader and deeper compared to the homogeneous case, particularly to the south of the overall slip
maximum. The introduction of a strong slab leads to a reduction in slip around the slip maximum near the trench. We
also find that details of the vertical deformation patterns for heterogeneous models are sensitive to the Poisson’s ratio.
While elastic heterogeneity does therefore not have a dramatic effect on bulk quantities such as inferred potency, the
mechanical response of a layered medium with a slab does lead to a systematically modified slip response, and such
effects may bias studies of mega-thrust earthquakes.
