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Lithospheric deformation induced by loading of the Hawaiian Islands and its implications for mantle rheology

The long‐term rheological properties of the lithosphere are fundamental for understanding both surface tectonics and mantle dynamics on Earth. In this study, we have developed 3‐D finite element models for computing the load‐induced surface deformation and stress for lithosphere and mantle with realistic nonlinear viscoelastic rheology including the frictional sliding, low‐temperature plasticity, and high‐temperature creep. We have determined the lithospheric deformation and stress due to volcano loading in the Hawaiian Islands region for the last few million years. By comparing model predictions with seismic observations of the depth to the top of oceanic crust and depth dependence of seismicity in the Hawaiian Islands region, we have sought to constrain lithospheric rheology. Our calculations show that the load‐induced surface deformation is controlled by low‐temperature plasticity and frictional sliding but is insensitive to high‐temperature creep. Lithospheric strength predicted from laboratory‐derived low‐temperature plasticity needs to be reduced significantly, and a frictional coefficient μf ranging from 0.1 to 0.7 is required in order to account for the observations. However, μf = 0.1 weakens the shallow part of the lithosphere so much that it causes the minima in strain rate and stress to occur at too large depths to be consistent with the observed depth distribution of seismicity. Our results therefore suggest a value for μf between 0.25 and 0.7. Finally, the maximum stress that accumulates in the deformed lithosphere beneath the Hawaiian Islands is about 100–200 MPa for models that match the observations, and this stress may be viewed as the largest lithospheric stress on Earth.