Normal fault thermal regimes: conductive and hydrothermal heat transfer surrounding the Wasatch fault, Utah

The thermal regime across an active normal fault is affected by tectonic pr ocesses of exhumation and erosion of the footwall and burial and sedimentat ion on the hanging wall. An enhanced thermal regime in the footwall is juxt aposed against a thermally depressed regime in the hanging wall causing sig nificant two-dimensional (2D) heat flow. These thermal processes have been simulated with 2D numerical models and applied to the Wasatch fault of cent ral Utah. Simulations included variable fault angles of 90 degrees, 60 degr ees, and 45 degrees and a vertical displacement profile accounting for hang ing wall and footwall tilt. After 20 m.y. of fault movement, 60 degrees fau lt, isotherms are displaced similar to 1 km on the footwall and hanging wal l. Furthermore, model surface heat flow is enhanced by 25% above the footwa ll and depressed by 15% above the hanging wall 10 km from the fault trace; the heat flow transition has a half width of 10 km. Present-day surface hea t flow was compiled for 23 sites along the Wasatch Front. Heat flow has a m ean value of 92 mW/m(2) (standard deviation 25 mW/m(2)) but, unlike model p redictions, does not show a discernible variation in heat flow across the f ault. Part of the discrepancy between predicted and observed conductive hea t flow may be caused by groundwater which recharges in the uplifted footwal l, is heated in the subsurface, and discharges as thermal water along the r ange bounding fault or into the hanging wall valley. Flow rates and water t emperatures from 29 tectonic hot springs along the Wasatch Front indicate a minimum hydrothermal thermal power loss of 90 MW or 0.24 MW per kilometer of strike along the fault. This thermal power is equivalent to a heat flow of 21 mW/m(2) captured uniformly between the range crest and range front, a nd discharged in hot springs. (C) 1999 Elsevier Science B.V. All rights res erved.