MI-97 Paleoseismic Investigation of the Cheraw Fault at Haswell, Colorado


This CGS publication reports findings from a recent paleoseismic investigation of the Cheraw fault in the southeastern plains of Colorado. The Cheraw fault is one of the few faults within the Central and Eastern United States (CEUS) known to have experienced a surface-rupturing earthquake during the Holocene. Despite this, relatively few studies have been conducted to characterize this particular fault. Principal investigators Dean Ostenaa and Mark Zellman based their report on the availability of new 1 m LiDAR data acquired specifically along the fault trace and results from two new trenches excavated near Haswell, Colorado.

Includes report, two plates (One, a LiDAR-based map of the Cheraw fault scarp, and the other, the detailed trench logs), and appendices. Digital PDF download. MI-97D

From the Introduction:

This report presents findings from new mapping of the Cheraw fault and from paleoseismic investigations near Haswell, Colorado. In 2016, Colorado Geological Survey (CGS) coordinated the acquisition of 1m LiDAR data along the mapped and extended trace of the Cheraw fault. Analyses of that data provides a basis for detailed mapping and extension of the fault scarp along the Cheraw fault to a total length of about 80 km. At the Haswell field site, the Cheraw fault scarp intersects the western edge of a pediment surface capped with early (?) Quaternary Nussbaum Alluvium. Previously, Zellman and Ostenaa investigated the site, delineated a fault zone, and established preliminary vertical offset estimates on the base of the Nussbaum Alluvium. In this investigation we excavate two trenches along the base of the Nussbaum Alluvium, and document Nussbaum Alluvium in nearby ditch exposures, to further characterize the fault zone and to constrain the paleoseismic history of the northeast section of the Cheraw fault.