|Scientific Investigations Report 2006-5176|
Entire document is available in PDF format: SIR2006-5176 (14.6 MB)
Document broken into smaller PDF files available:
Front (front cover to page 35, 5.23 MB)
Appendix 1 (pages 36-38, 171 KB)
Appendix 2 (pages 39-61, 371 KB)
Appendix 3 (pages 62-64, 274 KB)
Appendix 4 (page 65, 73 KB)
Appendix 5 (pages 66-back cover, 9.95 MB)
(Requires Adobe Acrobat Reader)
The citation of this report, in USGS format, is as follows:
Ball, L.B., Lucius, J.E., Land, L.A., and Teeple, A.P., 2006, Characterization of near-surface geology and possible voids using resistivity and electromagnetic methods at the Gran Quivira Unit of Salinas Pueblo Missions National Monument, central New Mexico, June 2005: U.S. Geological Survey Scientific Investigations Report 2006-5176, 101 p.
At the Gran Quivira Unit of Salinas Pueblo Missions National Monument in central New Mexico, a partially excavated pueblo known as Mound 7 has recently become architecturally unstable. Historical National Park Service records indicate both natural caves and artificial tunnels may be present in the area. Knowledge of the local near-surface geology and possible locations of voids would aid in preservation of the ruins. Time-domain and frequency-domain electromagnetic as well as direct-current resistivity methods were used to characterize the electrical structure of the near-surface geology and to identify discrete electrical features that may be associated with voids.
Time-domain electromagnetic soundings indicate three major electrical layers; however, correlation of these layers to geologic units was difficult because of the variability of lithologic data from existing test holes. Although resistivity forward modeling was unable to conclusively determine the presence or absence of voids in most cases, the high-resistivity values (greater than 5,000 ohm-meters) in the direct-current resistivity data indicate that voids may exist in the upper 50 meters. Underneath Mound 7, there is a possibility of large voids below a depth of 20 meters, but there is no indication of substantial voids in the upper 20 meters. Gridded lines and profiled inversions of frequency-domain electromagnetic data showed excellent correlation to resistivity features in the upper 5 meters of the direct-current resistivity data. This technique showed potential as a reconnaissance tool for detecting voids in the very near surface.