Evaluating the Regional-Scale Influence of Antecedent Soil Moisture on Seismically Induced Landsliding Using a Deterministic Landslide Initiation Framework
Abstract
Coseismic landslides commonly accompany earthquakes as destructive secondary hazards, resulting in loss of life and infrastructure in seismically active areas. High levels of soil moisture tied to antecedent rainfall may predispose hillslopes to failure during shaking, but due to the relative infrequency of large earthquakes in a given region and lack of associated landslide inventories with well-characterized soil moisture data, challenges remain in quantifying the influence of antecedent rainfall on coseismic shallow landsliding. In this study, we use RegionGrow3D (RG3D) - a three-dimensional (3D) slope stability approach that models landslide initiation on a regional scale - to assess discrete coseismic shallow landslides for a range of earthquake magnitudes and antecedent soil moisture conditions. Further, a 3D limit equilibrium approach is used to back-calculate soil shear strength and its associated uncertainty from inventoried landslides, enabling the assessment of landslide susceptibility. Through a case study in the Oregon Coast Range, USA, which lies in close proximity to the Cascadia Subduction Zone, we quantify the influence of antecedent soil moisture and coseismic acceleration on 1) regional landslide density, 2) geomorphic scaling relationships, 3) seasonal landsliding throughout the water year, and 4) spatial distributions of yield accelerations across a broad landscape. Further, we compare values of regional-scale landslide density stemming from earthquakes to those tied to extreme rainfall events for a range of antecedent moisture conditions. We find that coseismic landslide density, geomorphic scaling relationships, and yield accelerations are sensitive to seasonality, the relative wetness of a given water year, and shear strength uncertainty. Further, results suggest that higher peak ground accelerations from a higher magnitude earthquake may not always correspond to higher landslide area density, depending on the season and relative degree of soil moisture.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMNH25D0462M