Enlarge / The Castleton Tower in Moab National Park, Utah is a popular climbing destination.
Public Domain  Scientists at the University of Utah have conducted the first detailed seismic measurements of a columnar sandstone formation in Moab National Park, known as the Castleton Tower. The structure vibrates at two key resonant frequencies, according to a new publication in the Bulletin of the Seismological Society of America. That is, it is likely to withstand low to moderate magnitude earthquakes. The method developed by the team in Utah can also be applied to other natural rock structures to determine how susceptible they are to seismic and similar activities.
"In reality, we often view such great and outstanding landforms as enduring features of our landscape." They continue to evolve, "said co-author Riley Finnegan, a graduate student at the University of Utah." Because nothing is really static, Energy is always spreading across the earth, serving as a constant source of vibration for the rock. "
The research team has a full webpage dedicated to seismic recordings of natural resonances (vibrations) taken from the arches of Utah The arches are the stunning red rock formations in Castle Valley, 1
6 km from the city of Moab, and the team has accelerated the recordings into audible sounds that can flex, sway, and tremble in response to a number of factors: gusts of wind , distant seismic tremors, thermal stresses, local traffic etc. The arches often reinforce the Energy that goes through them when the frequencies are just right. Understanding this dynamics is crucial to predict how the structures will react in the event of an earthquake or similar disturbance. Despite extensive research on artificial civil structures, there has been little effort over the years to do so.
One of the biggest challenges in studying arcs is getting the first place required to perform these vibration measurements. Either the formations are limited (in order to better preserve them for posterity), or it is simply too difficult to attach sensors to hard to reach places of the formations. That's what makes this new record of environmental vibration from the 120 meter high Castleton Tower so significant.
"Until just a few years ago, there were virtually no measurements of this kind," said co-author Jeff Moore, a geologist at the University of Utah, who led the study. "Every function we measure is something new."
Finnegan and his colleagues managed to gather their data with the help of two experienced climbers. They were able to climb the tower and place seismometers at key points: at the base of the structure (for reference) and another at the top. The climbers stayed with the instrument for three hours while recording data, then climbed down to return it to the researchers.
The Utah team already knew from previous work that the unique geometry of higher structures such as the Castleton Tower will vibrate at lower temperatures – resonant frequencies that are smaller – similar to thick guitar strings, they have lower pitches than thin ones. The researchers' analysis showed two strong, different peaks in the data at 0.8 and 1.0 Hz, respectively, which they identified as the first two resonance frequencies of the structure. This makes the structure susceptible to strong earthquakes, which fortunately are rare in the region. Minor earthquakes – or minor shocks from traffic, construction equipment, or other environmental factors – are unlikely to resolve the tower's natural resonances from the impact of these forces on erosion rates and structural degradation over time, "said Moore, the model he and his students developed for Castleton Tower should also be applicable to other natural rock formations, taking into account factors such as height, slenderness, and material composition, which will help monitor changes in structural integrity over time.
"I hope that climbers and anyone lucky enough to stand in the shadow of this giant of stone will see this in a new light, "said co-author Paul Geimer, another Ph.D. student from Utah." Like the desert landscape where Castleton Tower is located he is dynamic and energetic and subtly responsive to changes in the environment. " DOI: Bulletin of the Seismological Society of America, 2019. 10.1785 / 0120190118 (About DOIs).