HR: 1340h
AN: U43B-1122    [Abstracts]
TI: Is source distribution of radiogenic heat generation inside the Earth's crust fractal?
AU: * Vedanti, N
EM: nimisha@ngri.res.in
AF: National Geophysical Research Institute, Uppal Road, Hyderabad, AP 500007, India
AU: Srivastava, R
EM: ravi_prakash@ngri.res.in
AF: National Geophysical Research Institute, Uppal Road, Hyderabad, AP 500007, India
AU: Dimri, V
EM: vpdimri@ngri.res.in
AF: National Geophysical Research Institute, Uppal Road, Hyderabad, AP 500007, India
AB: The crustal radiogenic heat sources contribute to about 40% of the heat flow at the surface in continental regions making this an important element in determining the crustal temperature distribution. Most of the radioactive isotopes are concentrated in the upper continental crust. In the absence of direct measurements of radioactive heat generation, various models for the depth distribution of radiogenic heat sources have been proposed in the literature out of which the exponential model is being widely used. However, we observed that variation of heat production rate in granites with depth in the three boreholes GPK1 & GPK2 (European Hot-Dry-Rock site in Soultz) and KTB, Germany is not exponential. Deviation from exponential model is evident at greater depths. We therefore argue that heat production in crust cannot be explained by a simple exponential model. Another opportunity to study more directly the variation of heat production with depth is provided by the lower crustal data from Western Canterbury region, New Zealand. At first look the heat production rate appeared to vary randomly between 0.92 and 2.39 micro w/m3 with the mean value of 1.56 micro w/m3, which is very much higher than the normal value taken for the lower crust assuming exponential model. This contributes to an important evidence for the deviation of the exponential model of heat production rate of lower crustal rocks. Study of rate of decrease in heat production with depth is necessary to consider the variations of heat flow with depth and heat flow extrapolation to greater depth is crucial to obtain the boundary conditions in various numerical models. Hence, to find an acceptable solution we carried out rescaled range analysis of the calculated heat production data of Soultz boreholes to understand the distribution. Value of Hurst coefficient obtained by rescaled range analysis of the data is around 0.84, which indicates that the radiogenic source distribution is more complex than a simple exponential model and may follow a fractal distribution. Hence, it may be necessary to employ the concept of fractal behaviour of these quantities in 1-D steady state heat conduction equation to compute the crustal and lithospheric temperature distributions.
DE: 4440 Fractals and multifractals
DE: 4475 Scaling: spatial and temporal (1872, 3270, 4277)
DE: 5418 Heat flow
SC: Union [U]
MN: 2007 Fall Meeting