Bouguer reduction density, why 2.67?

摘要

One of the most widely recognized parameters in solid-earth geophysics is the assumed density of the surface rocks of the continental crust, 2.67 g/cm~3, or 2670 kg/m~3 in today's preferred SI units. In the calculation of Bouguer and isostatic gravity anomalies, which are widely used for geological studies, the gravitational effect of the earth mass between an observation site and a datum is calculated assuming an infinite, flat slab of a specified density that approximates the mass. The datum for most surveys is sea level or, in the case of surveys of limited areas, it may be the elevation of the lowest station in the survey. Although the choice of datum is arbitrary, commonly sea level is used in an attempt to standardize anomalies from different surveys. Similarly, a density of 2.67 g/cm~3 is generally assumed for the density of the included mass in regional gravity surveys.