A Global Crustal Model
This global model of the Earth’s crust based on seismic refraction data published in the period 1948-1995 and a detailed compilation of ice and sediment thickness. A total of 560 seismic refraction measurement have been used to determine the crustal structure on continents and their margins. Oceanic crust is modeled with both a standard model for normal oceanic crust, and variants for non-standard regions, such as oceanic plateaus. Our model (CRUST 5.1) consists of 2,592 5 x 5 degree tiles in which the crust and uppermost mantle are described by eight layers: (1) ice, (2) water, (3) soft sediments, (4) hard sediments, (5) crystalline upper, (6) middle, and (7) lower crust, and (8) uppermost mantle. Topography and bathymetry are adopted from a standard database (ETOPO5). Compressional wave velocity in each layer is based on field measurements, and shear wave velocity and density are estimated using recently published empirical Vp-Vs and Vp-density relationships. (see crustal type)
A new aspect of this compilation is the use of statistics to predict crustal structure in areas without field measurements. In these unmeasured areas, the thickness of ice, water and sediments is taken from published compilations, and the velocity structure of the crystalline crust and uppermost mantle is estimated from the statistical average of regions with a similar crustal age and tectonic setting.
Our crustal model differs from previous models in that: (1) the thickness and seismic/density structure of sedimentary basins is accounted for more completely; (2) the velocity structure of unmeasured regions is estimated using a significantly larger database of crustal structure; (3) the compressional wave, shear wave, and density structure have been explicitly specified using newly available constraints from field and laboratory studies. We compare surface wave phase velocities predicted by our model with observations. There is close agreement between observed and predicted Love waves with a period of 40 s. These phases are primarily sensitive to the shear velocity and density structure in the upper 40 km. (see also Rayleigh wave anomalies) Our global crustal model is a significant improvement over previous models and is applicable to a wide range of geophysical calculations of Earth structure. We illustrate this with a simple calculation of crustal isostacy that shows good agreement between predicted and real topography, the difference (residual topography) mainly being due to lateral variations in the density of the uppermost mantle.