Spectral Amplification and Seismic Response of Rock Arches

Abstract:

Thousands of natural rock arches are located within the seismically quiet Colorado Plateau; however, increases in induced seismicity over recent decades raise concerns about the impacts of anthropogenic activity on these landforms. We compiled in-situ vibration measurements from several rock arches in addition to nearby bedrock reference sites, and compared site-to-reference spectral amplification ratios during ambient and earthquake conditions. We analyzed differences in arch response to varying earthquake magnitudes and distances, and found arch size, geometry, and frequency alignment between resonant modes and earthquake spectral content as primary factors controlling arch response to seismic inputs. Our results emphasize the importance of ideal sensor placements and overnight recordings to produce meaningful spectral amplification ratios, as improper placement, wind, and anthropogenic activity strongly skew ratios. These findings form the basis for estimating the onset of damaging vibrations, and broadly inform questions of co-seismic damage to these and similar landforms given an expected or experienced earthquake.