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Observations and models of lateral hydrothermal circulation on a young ridge flank: Numerical evaluation of thermal and chemical constraints

Geochemistry, Geophysics, Geosystems

Stein, Joshua

[1] We used a two-dimensional coupled heat and fluid flow model to investigate large-scale, lateral heat and fluid transport on the eastern flank of the Juan de Fuca Ridge. Cool seawater in the natural system is inferred to enter basement where it is exposed close to the spreading center and flow laterally beneath thick sediments, causing seafloor heat flow to be depressed relative to that input at the base of the plate. The flow rate, and thus the properties of permeable basement (the flow layer), controls the efficiency of lateral heat transport, as quantified through numerical modeling. We simulated forced flow in this layer by pumping water through at a fixed rate and quantified relations between flow rate, thickness of the permeable basement, and the extent of suppression of seafloor heat flow. Free flow simulations, in which fluid flow was not forced, match heat flow constraints if nonhydrostatic initial conditions are used and flow layer permeabilities are set to the high end of observed values (10-11 to 10-9 m2). To match seafloor heat flow observations, the models required lateral specific discharge of 1.2 to 40 m/yr for flow layer thicknesses of 600 to 100 m, respectively. The models also replicate differences in fluid pressures in basement, and the local distribution of pressures above and below hydrostatic. Estimated lateral flow rates are 10× to 1000× greater than estimates based on radiocarbon ages of basement pore waters. Estimated lateral flow rates based on thermal and chemical constraints can be reconciled if diffusion from discrete flow zones into less permeable stagnant zones in the crust is considered. © 2003 by the American Geophysical Union.

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TYPE Journal Article YEAR 2003
DOIOSTIScopus

Discrete sensor placement problems in distribution networks

Hart, William E.; Hart, William E.

We consider the problem of placing sensors in a network to detect and identify the source of any contamination. We consider two variants of this problem: (1) sensor-constrained: we are allowed a fixed number of sensors and want to minimize contamination detection time; and (2) time-constrained: we must detect contamination within a given time limit and want to minimize the number of sensors required. Our main results are as follows. First, we give a necessary and sufficient condition for source identification. Second, we show that the sensor and time constrained versions of the problem are polynomially equivalent. Finally, we show that the sensor-constrained version of the problem is polynomially equivalent to the asymmetric k-center problem and that the time-constrained version of the problem is polynomially equivalent to the dominating set problem.

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TYPE Conference YEAR 2003
OSTI
Results 89526–89550 of 99,299
Results 89526–89550 of 99,299