Geophysical exploration within northern Devils Lane graben, Canyonlands National Park, Utah: implications for sediment thickness and tectonic evolution

Seismic refraction profiling and gravity measurements along the length of the northern Devils Lane graben in Canyonlands National Park reveal that the bedrock floor of the graben is buried beneath a sedimentary cover more than 90 m thick, at least four to ten times more fill than previously measured. This sediment thickness, when combined with exposed fault topography, yields a throw of ≥145 m on the master fault. We estimate that horizontal extensional strain across the graben is on the order of 2–3%, and if this is typical of grabens elsewhere in Canyonlands the maximum average strain rates across the region are about 1×10−14 s−1, or ∼2 mm year−1. Our results indicate that published length to displacement relationships underestimate fault offset at Devils Lane by a factor of at least 1.5. This suggests that careful geophysical evaluation of sediment thickness elsewhere within the Canyonlands graben system, an important ‘type area’ for investigating the mechanics which characterize the formation of kilometer-scale extensional faults, may be required before these structures can be used to help define accurate fault length to displacement scaling laws.