An exploratory study of dislocation relaxation in polycrystalline olivine

Abstract

"Motivated by theoretical considerations of damped vibrations of dislocations and the need to better constrain global attenuation models, a laboratory study was undertaken of the attenuation of seismic waves and associated shear modulus dispersion in upper mantle olivine, (Mg{u2080}.{u2089},Fe{u2080}.{u2081}){u2082}SiO{u2084}. Polycrystalline olivine specimens were synthesised from laboratory (solution-gelation) and natural (San Carlos) precursors, hot-pressed and pre-deformed in the laboratory under high temperature.. and pressure (300 MPa). Compressive deformation experiments were performed for differential stresses up to 290 MPa and 22 % stsrain in the dislocation creep regime of olivine..... The observed relationship between dislocation-related dissipation and the orientation of the stress field during prior deformation suggests the possibility of seismological attenuation anisotropy. If dislocation damping is not grain size sensitive, then its operation in coarser-grained upper mantle olivine may contribute signigicantly to attenuation (Q{u207B}{u00B9} ~ 10{u207B}{u00B2}), especially in regions with relatively high levels of prevailing tectonic stress."--P. ix.