Seismology seismic waves

Most seismological constraints on mantle composition are derived by comparison of values of seismic wave velocities inferred for particular regions within the Earth to the values measured in the laboratory for particular minerals or mineral assemblages, with such comparisons being made under comparable regimes of pressure (P) and temperature (T). The primary parameters of interest, then, are the compressional (or P-) wave velocities (Vp) and the shear (or S-) wave velocities (Ej). These wave velocities are simply related to the density (p) and to the two isotropic elastic moduli, the adiabatic bulk modulus (Ks)... 

Experimentally, the bulk modulus is the simplest parameter to measure, but the seismological parameters of primary interest, Vp and Vg, both involve the shear modulus as well. It is convenient, therefore, to define a new parameter, the bulk sound velocity (V ), which eliminates all dependence upon the shear modulus (G) through a judicious linear combination of the squares of the two seismic wave velocities =... 

The seismological profile of the Earth s core (Figure 2) combined with the first-order relationship between density and seismic wave speed velocity (i.e., Vp = K 4/3p.)/p), =... 

Brune, j. Dorman, J. 1963. Seismic waves and earth structure in the Canadian shield. Bulletin of the Seismological Society of America, 53, 167-210. 

Donald W. Griffiths G.A. Bollinger. 1979. The effect of appalachian mountain topography on seismic waves. Bulletin of the Seismological society of America, 1979, 69 1081-1105. 

Shiann Jong Lee et al. 2009. Effects of topography on seismic-wave propagation an example from northern taiwan. Bulletin of the Seismological society of America, 99 314-325. 

Villaverde, Roberto. Fundamental Concepts ofEarthquake En neering. New York CRC Press, 2009. This book features a review of the history of the field of engineering seismology and includes some examples of how certain seismic wave types and other conditions are taken into account in building design. 

The shear and compressional acoustic wave velocities for the inner core are the direct output parameters from seismological observations. In order to make a direct comparison between the seismic data and measured physical properties, measurements of the acoustic velocities for iron at core pressures are required. Only very recently has it become possible to measure the elastic constants of s-Fe at high pressures and room temperature (Mao etal., 1999 Lubbers etal., 2000 Fiquet et al., 2001 Anderson et at, 2001). Recent advances in theory and computational methods have also provided new tools for computing the elastic constants of s-Fe at core pressures (Stixrude and Cohen, 1995 Soderhnd et al., 1996 Cohen et al., 1997 Steinle-Neumann and Stixrude, 1999) and core conditions (Laio et al., 2000 Steinle-Neumann et al, 2001 Alfe et al., 2001). There is considerable disagreement on the elastic constants of s-Fe between experimental results and theoretical calculations. The dilferences in the aggregate shear (FJ and compressional (Vp) wave velocities are smaller (Hemley and Mao, 2001 Steinle-Neumann et ai, 2001). Further improvement of theory and experiment is required to resolve the discrepancies. 

Evidence from seismology The science of seismology has profoundly influenced the way we think about the interior of the Earth. From the first estimate of velocity-depth curves for the Earth, obtained in the early part of the twentieth century a clear image has now emerged of the layered nature of the interior of the Earth. The synthesis of a huge amount of data derived from seismic body-wave travel times for P-waves... 

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