Geodetic evidence for aseismic reverse creep across the Teton Fault, Teton Range, Wyoming

Abstract

The valley block (hanging wall) of the central segment of the Teton fault rose 8±0.7mm during 1988 and 1989, relative to the mountain block west of the fault, a displacement opposite to that expected on a normal fault. The height change is based on first‐order leveling data over a 21.2km‐long fault‐crossing line of 42 permanent bench marks established and initially surveyed in 1988 and resurveyed in 1989. The rapid height change took place across a 1200m‐wide zone coincident with the steep escarpment at the base of the range front including the surface trace of the east‐dipping Teton fault, a major, active, range‐front normal fault bounding the east side of the Teton Range at the northeastern edge of the Basin and Range province. The total stratigraphic offset across the fault, as much as 9km, accumulated over the last 7 to 9 million years. Quaternary fault scarps, up to 52m in height, cut Pinedale (about 14,000 yr) glacial and younger fluvial‐alluvial deposits, indicating that the Teton fault has been the locus of several large, scarp‐forming earthquakes in the past 14,000 years, and it exhibits up to 25m of latest Quaternary displacement where crossed by the level line. Although the relative uplift of the hanging wall maybe local and unique to the Teton fault, this unexpected observation of aseismic, reverse creep may have a variety of tectonic and nontectonic causes, including hydrologic effects, aseismic fault creep or tilt, and pre‐seismic dilation.