THE LONG-TERM EFFECT OF EARTHQUAKES: USING GEOSPATIAL SOLUTIONS TO EVALUATE HEIGHTENED ROCKFALL ACTIVITY ON CRITICAL LIFELINES

Abstract

Rockfall is a chronic slope hazard along transportation corridors throughout the Pacific Northwest (PNW), resulting in frequent road closures and lane restrictions, and directly impacting driver safety, mobility, and accessibility for many critical lifelines. These impacts are amplified by moderate- to large-magnitude seismic events – both during and after shaking, making earthquakes a driver of persistent rockfall hazards. For this project, we performed continued monitoring of rockfall activity on a series of rock slopes via repeat terrestrial laser scanning, geologic characterization, and imagery collection. These data, as well as custom-generated shakemaps and a database creation (Alaska GAM, ODOT unstable slopes database) of rockfall events throughout the PNW and New Zealand, enable extrapolation of potential coseismic and post-seismic hazards to a variety of earthquake scenarios in Alaska. We extend and modify the Rockfall Activity Rate System (RoARS) model to rock slope sites in two Alaskan transportation corridors to evaluate coseismic and post-seismic rockfall hazard at a regional scale, as well as estimate rockfall volumes and associated closure times. We find that both corridors are prone to earthquake-induced rockfall activity, but the magnitude and long-term persistence of this activity is highly dependent on the given rupture event, as are closure times along each corridor. While scenario-dependent, this database and model creation explores a new avenue for decision-makers to evaluate potential rockfall scenarios considering seismic disturbance, and consequently, plan accordingly for closures and restoration of mobility following shaking.