Geophysical Exploration in Canyonlands National Park, Utah

Canyonlands National Park in Utah is home to some of the most spectacular kilometer-scale graben exposures in the world. For decades, structural geologists have been studying the grabens in detail to improve our understanding of the mechanical processes that control and characterize normal fault growth. One relationship that has been proposed is that there is a consistent scaling relationship between the length of a fault in map view and the total dip displacement of the same fault. This relationship clearly applies to populations of smaller faults across several orders of magnitude, and if it holds for kilometer-scale fault systems like those in Canyonlands there are exciting implications for planetary science - normally one can only see and measure the map-view length of a fault, but knowledge of the fault displacement allows calculation of how much extension has occurred across faulted regions, a very important consideration when studying tectonic deformation of planetary surfaces.

The challenge in understanding fault length-displacement scaling in Canyonlands is that the floors of the grabens are covered with sediment, and thus the total displacement of the faults can't be measured directly in most instances. The goal of my research effort in Canyonlands, a collaborative effort with Dr. Richard Schultz ( University of Nevada Reno, NV ) and Dr. Glenn Kroeger ( Trinity University, TX ), is to use non-invasive shallow geophysics - seismic refraction and gravity thus far - to constrain the along-axis thickness of sediments within individual grabens. When integrated with existing structural measurements, these data provide a way to measure the total fault displacement as a function of along-axis length in individual Canyonlands grabens for the first time.

The results to date? In a nutshell, the sediment thicknesses are much greater in all areas studied to date than had previously been supposed! And the work continues.

I'd like to express my heartfelt gratitude to the personnel of the National Park Service for facilitating access to the grabens!

Cheers,

Eric B. Grosfils