Statistical analysis of factors influencing overall rockfall activity and the spatially-normalized rockfall power law activity constant, Ast

Abstract

Natural and human-constructed rock slopes pose a hazard to humans and infrastructure in mountainous areas around the world. Rockfall inventories provide a basis for slope-scale or regional rockfall hazard assessment, improving the ability for management agencies to make informed mitigation decisions. A power law relating rockfall volume to frequency is commonly used to represent the volume distribution of a rockfall inventory to quantify hazard and forecast the recurrence interval of future events. This power law can be spatially normalized by the relevant rockfall source zone area to allow for direct comparison of rockfall activity at different slopes.

This work focuses on statistical analysis of geological, climatic, and database (non-physical) variables potentially affecting the vertical scaling of the rockfall power law. 44 rockfall inventories from the literature were used to assess whether relationships exist between independent variables and power law metrics for overall rockfall activity with a focus on the spatially-normalized activity constant, A_st.

Monitoring frequency and monitoring method were found to have a large, statistically significant effect on apparent rockfall activity due to the intrinsic limitations of observational rockfall inventories. Isolation of terrestrial remote sensing inventories showed that the most important variables influencing overall rockfall activity (to varying degrees) are lithology, rockmass condition, number of annual freezing degree-days, and whether the slope is natural or cut. Focusing future research on the effects that these variables have on rockfall activity has the potential to improve inventory-derived and field-based rockfall hazard assessment.