Flow of Lower Crust and Upper Mantle Inferred from Geological and Geophysical Observations

Abstract

Flow properties of lower crust and upper mantle are important parameters for better understanding geodynamics. In particular, they are crucial for quantitatively evaluating the process of stress accumulation and relaxation of seismic faults associated with transient crustal deformation, such as post-seismic deformation. Recent activities to illuminate the rheological properties of lower crust and upper mantle are reviewed based on geological and geophysical observations. In particular, large, transient crustal deformation places robust constraints on the rheological properties. Careful observations of exhumed fault rocks limit the range of stress levels in the lower crust and upper mantle. Localized flow in the upper mantle from post-seismic observations can also be constrained. Combining detailed geodetic observations and numerical simulations, taking into account various rheological properties of rocks, can constrain the heterogeneity of viscosities possibly related to the heterogeneities of temperature and water content distribution. Furthermore, recent activities to infer rheological heterogeneity from an inversion analysis are also introduced. Under well constrained conditions, nonlinear flow properties of the upper mantle can be estimated. These activities clearly indicate that various aspects of the rheological（flow）properties of lower crust and upper mantle can be extracted from the analyses.