Current Research in EEPS: Dr. Lars Hansen, University of Minnesota
From mega-annum to microseconds: the role of crystal dislocations in the dynamics of the solid earth
Large-scale geodynamic processes in the solid Earth often depend intimately on small-scale defects within the constituent minerals. These processes span a wide range of time scales and include convection in the upper mantle, flexure of the lithosphere, glacial isostatic adjustment, postseismic creep, and frictional sliding on faults during earthquakes. Here I describe the influence of dislocations, a particular type of crystal defect, on this range of processes within upper-mantle rocks. The role of dislocations across these timescales is elucidated by a series of laboratory experiments including synchrotron-based experiments to measure yield stress and strain hardening, high-temperature uniaxial tests to investigate anelasticity, and dynamic indentation using ball-drop experiments to assess mineral strength at extreme strain rates. These different experimental approaches are linked through the dynamics of dislocations. The resulting model of dislocation-based deformation resolves conflicts among previous geophysical observations and provides a series of new predictions about the mechanical properties of rocks at both slow and fast timescales not typically accessible in the laboratory.