Modal Analysis of Landscape and Double-O Arches

Thursday, 18 December 2014
Jeffrey R Moore1, Alison Dorsey1, John R Wood2, Michael Scott Thorne1 and Eric Bilderback2, (1)University of Utah, Geology and Geophysics, Salt Lake City, UT, United States, (2)National Park Service, Geologic Resources Division, Lakewood, CO, United States
We combine in-situ ambient vibration measurements with 3D numerical modeling to study the resonance characteristics of two prominent arches in Arches National Park, Utah: Landscape Arch and Double-O Arch. We placed broadband seismometers on each arch and recorded up to three hours of ambient seismic data. Identified spectral peaks are interpreted to represent resonant frequencies of the arches, and further studied for their polarization attributes. We developed 3D models of each site using ground-based photogrammetry in order to perform numerical modal analyses. Assigning representative material properties, we are able to match the measured fundamental frequency of each arch, as well as certain higher-order resonant frequencies. Landscape Arch is the longest arch in North America and is remarkably slender, while Double-O Arch is a prominent visitor attraction. Repeat ambient vibration measurements over time will be used to assess changes in resonance characteristics, which in turn provide evidence of internal mechanical change. Our goal is to understand how the arches respond to their environment, and ultimately be able to assess progressive damage of these iconic features.