Seismic and Acoustic Investigation of Rock Fall Processes

Why Study Rock Fall with Instruments?

Rock fall is a natural hazard that is present in steep mountain environments worldwide. Rock falls present a significant risk to people and infrastructure such as roads, dams, tunnels, homes, and reservoirs. The steep and dramatic topography of Yosemite National Park attracts millions of visitors, but is also susceptible to the rock fall hazard. Almost 600 rock failures were documented during the period 1851 to 2008, resulting in 14 fatalities. Yosemite Valley is therefore an excellent site to study rock fall processes, where lessons learned can be directly applied to risk management.

Rock falls in Yosemite are currently reported and recorded based on eyewitness reports only; as such, rock fall processes are not well-understood, and many rock falls likely go unnoticed. Seismic instruments can detect and differentiate rock falls from other seismic activity, and provide a complete record of rock falls unbiased by the presence or lack of eyewitnesses. The main objective of this project is to detect and catalog rock falls to obtain a better understanding of the rock fall process and causative events such as freeze-thaw, water seepage, heating and cooling.

Large rock falls are accompanied by loud rumbling noises, dust clouds, and often, boulders impacting rock ledges and talus slopes. There have been numerous anecdotal reports of precursors to rock falls in the form of loud cracking noises and a showering of small pebbles and rocks. The frequency of precursors in Yosemite is entirely unknown, and searching for them is a major objective of this project.

Field Research