Southwestern flank of the Oquirrh Mountains showing the alluvial fans and location of the fault scarp at Mercur Canyon. The mountains are located about 60 km southwest of Salt Lake City in the eastern Basin and Range. (False color image from ASTER sensor showing vegetation in red. )
Quaternary geology map of the Mercur Canyon alluvial fan. Inset shows the locations of paleoseismology trenches excavated and logged by Olig et al. (1999) and seismic lines for tomography (See Mattson, 2004).
Introduction: The Mercur Fault is located along the south and western flank of the Oquirrh Mountains about 60 km southwest of Salt Lake City, Utah. Earthquakes during the late Pleistocene and Holocene created a spectacular fault scarp in an alluvial fan that extends outward from the mountain front (Fig. 1). We use this scarp as a test site for combining high resolution seismic tomography and drilling in Quaternary deposits to evaluate the history of faulting over a period of several hundred thousand years. The work is summarized in the following pages which discuss the geological setting, present a sample of a high-resolution tomogram, the drilling and coring work, and our preliminary interpretations. Previous work at this site included trenching by Olig and others (1999). The paleoseismology trench provided shallow depth control to help constrain the interpretation of the seismic tomograms and drill cores, which extended to considerably greater depth than the paleoseismology trench. The work shown here was done by Dr. Ann Mattson as part of her post-doctorate project (Mattson et al. (2003); Mattson, 2004). (Click on each figure to see it at full size.)
Mercur fault scarp on video frame from our radio controlled aircraft. View to southwest.
Physiographic and Geological Setting