2018 Anchorage Alaska Rockslope Laser Scan Surveys

Earthquakes cause many hazards during shaking, but some of the hazards linger long after the seismic event is over. For example, heightened frequency of landslides and rockfalls commonly occur in the months - and even years - following an earthquake. This Rapid Response Research (RAPID) project seeks to capture perishable data from several rock slopes highly susceptible to rockfall that were affected by the recent earthquake in Anchorage. By doing this, we may compare the rate and frequency of rockfall occurrence to pre-earthquake levels in order to better understand how much rockfall activity increases following shaking, and how long it takes to return to pre-earthquake levels. This has implications for post-earthquake recovery and seismic resilience throughout much of the US and abroad.

Earthquakes often trigger significant rockfall activity in steep cliffs. The recent 2018 November 30th Alaska earthquake caused significant shaking (up to 0.4g) across the Anchorage region, resulting in numerous rockfalls, landslides, and lateral spreads. The combination of potentially large volumes, high velocities, long travel distances, and impact forces make the rockfall hazard significant. Based on observations from past events in New Zealand, it is believed that rockfall activity over at least the next several months will exceed "normal" baseline levels before decreasing. Nevertheless, as is often the case, the previous research does not have detailed baseline information prior to the event. This prior research begs three primary scientific questions: what is "baseline" rockfall activity? How does shaking translate to increased rockfall activity, magnitude, and frequency particularly in the heterogenous geologic conditions encountered in the rock slopes surrounding Anchorage? And lastly, how quickly does rockfall activity and magnitude return to baseline conditions? This project seeks to collect rockfall activity rates through repeat terrestrial laser scanning at well-characterized rockfall sites near Anchorage. Change detection will be performed and the rate of rockfall activity characterized in comparison to previous epochs and the serial data collected as part of this project. With existing baseline data not influenced by recent seismic activity, we will characterize and compare the activity rate following shaking. This investigation will provide fundamental knowledge about the process that dictates both the increase and decay in rockfall activity after seismic disturbance. The resulting knowledge will provide data needed to support and advance modern performance- and risk-based extreme event design methodologies.