STRAIN ACCUMULATION ACROSS THE WASATCH FAULT NEAR OGDEN, UTAH

Deformation of a 70 by 40-km trilateration network spanning the north trending Wasatch fault near Ogden, Utah, has been monitored from 1972 through 1990. All but nine of the 200 measurements are consistent with deformation that is linear in time. We presume that those nine observations are contaminated by some blunder in making the measurements and that deformation is linear in time. The strain rate over the 1972-1990 interval across a 40-km-wide zone west of the Wasatch fault (hanging wall block) is adequately approximated by a 0.04 +/- 0.01-mu-strain/yr N85-degrees-E +/- 5-degrees uniaxial extension. Adequate coverage of the footwall block is available only over the 1981-1990 interval, and the strain rate across a 30-km-wide zone there is approximated by a 0.07 +/- 0.03-mu-strain/yr N20-degrees-E +/- 12-degrees uniaxial extension. The observed extension of the hanging wall block in the direction normal to fault strike suggests that the Wasatch fault may be listric; a planar fault would produce a zone of contraction normal to the fault at the surface of the hanging wall block. The component of extension parallel to fault strike observed on the footwall block is unexplained.