1. Elasticity of MgO- Frequency Dependence Hoda Mohseni and Gerd Steinle-Neumann 1. Introduction Fig 2. MgO crystal structure 3. Experimental methods used to study elastic properties of MgO 0kHzMHz GHzTHzPHz Computation Seismic wave Ultrasonic resonant Ultrasonic MHz Ultrasonic GHz Neutron scattering Inelastic X-ray Static compression Phonon sideband Brillouin spectroscopy Fig 1.experimental methods at ambient and high pressure Our most precise and informative observation of the Earth’s interior comes from seismology that maps elastic properties. In the inversion of Earth structure seismology uses information from body waves, surface waves and free oscillation. They differ in type of displacement and their frequency range, covering 0.1 mHz to 10 Hz, but their interpretation is based on laboratory experiments and computational work in mineral physics which operate at very different frequencies: experiments are typically performed at much higher υ; however, static compression experiments and computations yield zero frequency results (Fig.1). The reason that makes elastic properties so important in geophysics comes from the fact that they are related to K and μ and the change in density that occurs when minerals are compressed. Thus, the knowledge of the elastic properties of minerals is essential for interpreting the seismic properties of Earth. We explored the frequency dependence of elastic properties of MgO.  MgO is the second most abundant mineral phase existing in Earth’s lower mantle (Mg, Fe)O.  MgO is regarded as a prototype oxide due to its cubic B1 structure (Fig.2).  MgO has only three independent elastic constant: C 11, C 12 and C 44.  MgO is stable in the B1 structure over a wide range in P-T space. 2. Why MgO?! 4. Result Fig 3. Longitudinal, off-diagonal, shear elastic constants at ambient P and T as a function of frequency from different experimental studies. Fig 4. Zero bulk and shear modulus for MgO at ambient P and T as a function of frequency from different experimental studies. Fig 5. Shear (left) and bulk (right) modulus for MgO as a function of frequency from different experimental studies at 5 GPa and ambient T. Fig 6. Shear (left) and bulk (right) modulus for MgO as a function of frequency from different experimental studies at 1000 K and ambient P. References: The data points are from AA66 - Anderson and Andratch, J. Am. Ceramics Soc. 8, 404, [1966], C96 - Chopelas, Phys. Chem. Minerals. 23, 25, [1996], F08 - Fukui et al., J. Syn. Rad. 15, 618, [2008], I89 - Isaak et al., Phys. Chem. Minerals. 30, 157, [1989], JN83 - Jackson and Niesler, in High Pressure Research in Geophysics, 93, [1983], J02 - Jacobsen et al., J. Geophys. Res. 107, B2203, [2002], J00 - Jacobsen et al., Jacobsen et al., J. Geophys. Res. 107, ECV 4, [2009] K10 - Kono et al., Phys. Earth Planet Inter. 183, 196, [2010], M09 - Murakami et al., Earth. Planet Sci. 277, 123, [2009], O94 - Oda et al., J. Geophys. Res. 99, 15517, [1994], S83 - Sumino et al., Phys. Chem. Minerals. 9, 10497, [1983], S70 - Spetzler, J. Geophys Res. 106, 515, [1970], SB00 - Sinogeikin and Bass, Phys. Earth. Planet Inter. 120, 43, [2000], S00 - Sinogeikin et al., Phys. Earth Planet Int. 120, 43, [2000], Y90 - Yoneda et al., J. Phys. Earth. 38, 19, [1990], Z00 - Zha et al., Proc. Nat.l Acad. Sci. 97, 13494, [2000]. 5.Conclusion  In this literature survey, we have compiled elastic constant and aggregate moduli data for MgO from various experimental techniques (i.e., different frequencies. Ultrasonic devices provide frequencies between 10 6 and 10 10 Hz in which the spectrum of measurements is almost continous, while higher frequencies are available only in Brillouin spectroscopy (10 14 Hz) and IXS (10 17 Hz) measurements.  At ambient condition, for none of the elastic constants or aggregate modui, a specific frequency dependence has observed. The same holds for experiments at high pressure where we have compiled data at 5 GPa.  At room pressure and high T, a trend is observable with both bulk and shear moduli decreasing frequency.  Based on our complication it appears that –aside from possible anelastic effect –the elastic moduli obtained in laboratory for a relatively stiff material like MgO can be used for the interpretation of seismologic results. υ