In this talk, we first examine how microphysical models of transient deformation might manifest at the macroscale which may be summarized as a distinct frequency dependence of dissipation that extends beyond typical models used within geophysics (e.g., Maxwell and Burger viscoelastic models). We will explore several seismological, geodetic, and geological observations that show a strong indication of the activation of transient deformation. These examples include seismic normal modes and tides that span minutes to decades, and observations of viscoelastic rebound in the response to melting ice sheets at time scales from weeks to thousands of years. For these, we will feature examples from Antarctica and Greenland. In all our cases we demonstrate that laboratory derived constitutive laws describing a full spectrum of deformation mechanisms can help to reconcile different inferences of viscoelastic structure.To arrive at these conclusions, theoretical and observational insights from a wide range of spatio-temporal data (the microphysical and planetary-scale) and disciplines (rock physics, seismology and geodynamics) have been combined. The talk will end with implications of the importance of considering transient deformation in other examples of Earth dynamics and associated challenges that remain.

Seismic-frequency torsional forced-oscillation measurements of shear modulus dispersion and associated strain-energy dissipation under conditions of simultaneously high temperature and pressure in our laboratory require the specimen to be enclosed within a thin-walled metal sleeve – typically of mild steel. However, the well-known transition between the austenite and ferrite phases on cooling across the interval 900-700ºC complicates its mechanical behaviour. The resulting uncertainty tends to mask the seismologically important onset, within this temperature range, of appreciably anelastic behaviour of polycrystalline olivine. In order to more closely document this important transition in mechanical behaviour, we have conducted an unpublished study in which of a specimen of polycrystalline olivine is jacketed within a copper sleeve which retains its face-centred-cubic (fcc) structure throughout the range of the measurements limited to 1050ºC by the proximity of the melting point. Here we report measurements to higher temperature (1200ºC) in which we employ austenitic (fcc) stainless steel (SS) as an alternative jacket material. Two parallel reference experiments with a SS-jacketed SS specimen and a SS-jacketed sapphire specimen were also conducted to obtain the mechanical properties of the jacket material. Such information concerning the viscoelastic behaviour of SS is used to subtract the torsional stiffness of the SS jacket from the properties of SS-jacketed olivine and thereby isolate the mechanical behaviour of olivine. The resulting dissipation spectrum for the olivine specimen consists of a monotonic background dissipation with a superimposed peak located within the 1-1000 s period range for temperatures between 900 and 1050ºC. The dissipation peak and associated shear modulus dispersion, potentially attributable to elastically accommodated grain boundary sliding, display an Arrhenius dependence upon temperature - moving systematically to shorter periods with increasing temperature. Comparison of the results obtained for sol-gel Fo90 olivine specimens enclosed within the alternative mild-steel, copper, and stainless-steel jackets will provide new insight into the nature of the seismologically important transition between the elastic and anelastic regimes.