Heat flow variations from bottom simulating reflectors on the Cascadia margin

A bottom simulating reflector (BSR), representing the base of the gas hydra te stability field, was observed over a closely spaced grid of seismic line s on the continental slope of the northern Cascadia margin. A simple conduc tive model was used to calculate heat Row from the depth of the BSR. A regi onal trend was observed, in which heat flow decreased landward across the m argin from an average of similar to 80 mW/m(2) at a distance of 15 km from the deformation front to similar to 65 mW/m(2) at a distance of 40 km. This trend reflects the processes of tectonic thickening of accretionary wedge sediments and subduction of the Juan de Fuca plate, and contrasts with the near-constant heat flow across the Oregon margin where the dip of the subdu cting plate and thus the rate of sediment thickening are slightly smaller. Consistent local variations were also observed, notably low heat how values over prominent topographic highs and high heat flow values over the flanks of the topographic highs. At some localities over a horizontal distance of 1-2 km, heat how increased by as much as 50%, from typical values of 65 to 100 mW/m(2). Much of this variation may be due to focusing and defocusing effects of the topography alone, and indicates the importance of carrying o ut topographic corrections to heat how in regions of significant relief suc h as the continental slope. However, a component of the local heat Row patt erns may be due to dynamic effects, including the displacement of isotherms by thrust faulting and the upward migration of warm fluids along permeabil ity channels such as faults. (C) 2000 Elsevier Science B.V. All rights rese rved.