Abstract:
Of all geophysical properties, the temperature distribution within the earth is perhaps the moat fundamental, because so many properties are temperature dependent. To solve the boundary value problem of temperature distribution within the earth, both the initial and boundary conditions must be known, together with such parameters as density, thermal capacity, etc. The only directly measurable quantity is the boundary condition which is obtained by measuring the heat flux through the earth's surface - this is termed the 'Terrestrial Heat Flow'. On a world-wide scale the measurement of terrestrial heat flow enables the boundary condition to be specified and also gives an order of magnitude to the thermal energy available for geophysical processes. The thermal energy available has become important in recent years as a mechanism to perpetuate continental drift via the process of mantle convection. The distribution of heat flow has verified the existance of convectional cells by revealing regions of high and low heat flow corresponding to upwellings and downwellings. These appear to be large scale features, and closely follow the ocean ridges and trenches. However the small scale variation of heat flow is also important, although to date the regions investigated are very few. For economic reasons the regions studied have been those with active geothermal properties, such as Wairakei in New Zealand and the Tuscan thermal district in Italy. (Banwell 1963; Elder in 'Terrestrial Heat Flow' 1965). These regions thus can not be representative of a 'normal' region, but as yet this so called 'normal’ region has not been defined because of lack of measurements. Measurements on land have been confined to regions where boreholes have been drilled for some other purpose, such as oil exploration etc. and thus detailed surveys have only been carried out in regions which are geologically interesting.
