Downward continuation of heat flow data

Abstract

Abstract Downward continuation operators are derived and used to calculate the subsurface temperature from surface heat flow data. If the distribution of the shallow heat sources were known, their effect on the temperature field could be included in the downward continuation operator. The distribution of heat sources with depth can be estimated from the Fourier spectral content of the heat flow data, but the relationship is non-unique. Several operators have been derived with different assumptions regarding the relationship between the wavelength of the surface heat flow variations and the depth of the corresponding heat sources. These downward continuation operators were applied to determine the subsurface temperature and the deep heat flow beneath the Colorado Plateau; the calculations show that the temperature in the crust beneath the plateau is lower than in the surrounding Basin and Range and Rio Grande Rift Provinces. However, the temperature is locally higher in regions of recent tectonic or magmatic activity. The same downward continuation operators can also be used to model the effect of hydrothermal convection on the temperature field. An example is presented where closely spaced heat flow data from the Juan de Fuca Ridge have been used to calculate the crustal temperature and to estimate the heat flow below the convecting layer.